• Member Since 2nd Nov, 2012
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Admiral Biscuit


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More Blog Posts890

  • Tuesday
    March Music Monday 4

    March Music Monday 4

    For all the :yay: . . . guff I pile on my manager, he occasionally dispenses pearls of wisdom, or names songs that it turns out that I really, really like.


    Source

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    26 comments · 171 views
  • 1 week
    March Music Monday 3

    I think I mentioned in the first one of these that my manager always plays the same top-40 Country station all day every day.


    Source

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    14 comments · 210 views
  • 2 weeks
    March Music Monday 2

    Alrighty fellow music lovers, it's another Monday in March, and you know what that means!

    ... 'cause you read the title :heart:


    Source

    This one doesn't have as much of a back story.

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    9 comments · 212 views
  • 3 weeks
    March Music Monday 1

    This is pretty much what it says on the tin.

    See, ponies like music, I think that's pretty well-established canon. I like music, too, and I thought I'd introduce you to some music you might not have heard before. After all, I've been introduced to music by other people through the years, oftentimes something I'd never have found on my own.

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    29 comments · 295 views
  • 5 weeks
    MECHANIC: The Most Boring One Yet

    I hesitate to even suggest you grab your favorite beverage, you're just gonna skim this one. But, if you're game:


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    17 comments · 318 views
Sep
29th
2017

Vehicle Computer Networks · 1:43am Sep 29th, 2017

I've promised this blog post and then I kinda forgot about it; luckily, one of the vehicles I got to work on today was a nice reminder. Like a sharp stick to the eye.


Source
This isn't the actual truck, but it's essentially the same



Back in the primitive days, cars had simple computers. Really, the first thing that computers did was replace the distributor and the carburetor. They had a few inputs, and the only things they could really control were the fuel delivery and the spark timing. And that was it.

(Of course, this was the eighties, and an Apple ][e was high tech.)

Now, I know some of you are going to grumble about the good old days and how simple things were back then. And trust me, I'm going to cover this, but I've got to go slightly off-topic for a bit.

I've been the proud owner of nearly a dozen s-10 pickups. Not all of them whole, and most of them not running, but nearly a dozen. So that makes me sort of an expert, I guess.

Anyway, two in particular come to mind. I had an '84 extended cab 4WD which I drove for a few years, and I also have an '88. The '84 was a 2.8L carbureted motor, while the '88 had fuel injection.

We're not going to talk about the carb on the '84 except to say that it did stuff. I'm not old-school enough to be that familiar with carburetors, to be honest. And since the truck ran, I presume that it did the stuff it was supposed to do.

Ignition timing is a function of engine speed, engine temperature, and engine load (mostly). A computer can calculate that pretty efficiently, but if you haven't got one, you have to use other methods. Things like centrifigual advance (weights and springs), and vacuum advance (a vacuum pot). And you can fine-tune it with delay valves and thermal valves . . . anyway, here's a look at the vacuum diagram for that truck:


Source

If you're brave enough to follow it, you'll find things like "TVS" (thermal vacuum switch; only engages when a temperature target is met) and "Delay Valve" (fairly self-explanatory), and Check Valve (only works one way), and Non-Linear Valve (I guess it's a parabola?), and VAC RSVR W CHK VLV (engineers do cocaine), and . . . .

My '88 did the same thing, except better. And it didn't have any vacuum lines to the distributor.

As you can see, there are advantages to using a computer.


For a while, the only thing that the computer got to play with was the engine. But as computers became faster and cheaper, it was obvious that they could perform other tasks. One example: anyone who has a car with power windows likely has a group of switches on the driver's side door to control all the windows. Back in the old day, that meant running big, fat wires from there to every door on the car. But with a computer, all you need is a thin data line that can tell a computer in another door what you want to have happen. Basically, you can have two fat wires that carry all the pixies to each door, and then two little wires that talk, and everything else can be done internally.

The same holds true for other systems. My '88 is simple; it has a speedometer cable and then on the back of the instrument panel cluster, there's a pickup coil by the cable, which tells the PCM how fast the truck is going. That's been broken for years, and the computer is so dumb it doesn't know. It just assumes that I'm revving the engine for hours at a time and not going anywhere.

Newer vehicles are much better at self-diagnosis . . . but that's a topic for later.

It was also obvious that there were pieces of information that ought to be shared between systems. Obviously the PCM needs to know how fast we're going, but so does the cruise control, the antilock brakes, traction control, airbag, etc. Rather than run one signal to each component, why not just have one module get the information, and then tell all the other ones who want to know? Much simpler, and also cheaper.

Clearly, to get all this functionality, you need a network. And here's where things get interesting.


At first, they were fairly simple; maybe you had your PCM and ABS and TCM all networked together and sharing information, and you could send what data you needed to your instrument panel via the PCM or the ABS module. And maybe you've got a security module . . . and that ought to communicate with a body control module, so it knows when doors are opened or closed, and it can honk the horn and flash the lights. Of course, it's also got to report to the PCM, to make sure you're using the right key. And now we've got factory-installed remote start . . . so the RKE module gets the signal from the remote, tells the BCM, who tells the VSM, and they collectively tell the PCM to start the engine if the TCM says that it's in park . . .

This brings us to our first case: the Dodge Ram.

We'd had this truck a month or two ago, and it had a bad engine. So the customer took it away, and then as a father-son bonding project, they installed a rebuilt engine in it. And when they got done everything was perfect.

LOL.

So it got towed back to us, because now it wouldn't crank.

I got out the scan tool, and fairly quickly determined that I couldn't talk to the PCM, but I could talk to every other module on the truck. I also discovered that the instrument panel cluster (IPC) also couldn't talk to the PCM. Also the red “Security” light was on.

My working hypothesis was that the vehicle saw the start request, but since there was no network communication, the starter never got the message to crank the engine.

One thing that is a very useful tool for mechanics—and one that's often overlooked—is a network topology map. It tells you how all the different modules talk to each other, and by determining who's alive and who isn't, you can narrow your search for the network failure.

My first guess was that they'd managed to break a wire, or else forgotten to plug a connector in that went through the firewall, since everything inside the truck seemed to work, and stuff outside was less certain. But when I looked at the wiring diagram, it was obvious that wasn't true; the ABS module was spliced into the network underhood, and I could talk to that.

Still, that really narrowed down the search, since I now knew where the fault had to be. Either the network wire was broken between the PCM and the splice, or else the PCM was dead.


Y'all remember my “It's not Lupus” blog post? Well, I haven't been totally straightforward about this truck; let's just say that on the scale of monkeys to professional technician, this engine install was heavily biased towards the monkeys end of the spectrum. While I can't think of a way that you could kill a PCM installing an engine, this dynamic duo probably could have come up with one.

And it turned out I was right.

My manager suggested that since the PCM was easy to get to, a good first step might be to unplug all the connectors and see if maybe they'd bent a terminal. I didn't find that, but it wasn't a wasted exercise; when I unplugged all the wires, I also found this:

It's safe to assume that when you've got a bundle of ground wires that big, at least one of them must be important for something, and indeed, as soon as I reconnected them, the PCM came to life, and the truck started.


Another important thing about networks is that most cars these days have several, and they operate at different speeds. Fast pixies are expensive!

That's something that the engineers can get away with, because there's some stuff that you need to have happen RIGHT NOW and other stuff that can sort of wait (bear in mind we're talking electronics speed here, not wait service at Denny's speed). To use rather extreme examples, if you want to turn on the rear window defroster, it's okay if it takes a second or two before it actually happens; whereas if the airbag needs to go off, it had better happen in milliseconds, or else it's already too late.

So to make things easier on the computers, you tend to have CAN buses (fast) and LAN buses (medium or low speed). Sometimes there is more than one; mid 2000s GM tended to have a CAN bus, and a medium and low speed LAN bus.

There are some times that the message needs to be sent from one network to another, and in those cases you have a module which is called a gateway, who can talk on multiple networks. Sometimes it's a dedicated module, while other times it's a function of some other module.

And this brings us to the Impala.

The most astute readers have probably already guessed what the diagnosis is going to be, and good on ya. I had no idea going in.


Before we get started, I'm going to give you a fundamental engineering protop: Systems ought to fail safe. If you remember the Chevy truck that had opposing symptoms—the one that needed the radio disconnected and a transmission range switch—you'll remember that when the computer knew that something was wrong with the transmission range switch, it simply didn't let the truck start. Better to be stuck in a parking space with a truck that won't run than having one that starts up in gear and drives out of your garage and into the alleyway behind your house before you can react (why yes, that is personal experience). If the IPC doesn't get a message from the ABS module saying all is good, it's best to assume that the ABS module has failed. And if there's something hinkey with the brake switch, it's probably best to not allow cruise control, since it might not turn off when you hit the brakes.


The Impala came in with a deceptively simple symptom: “customer states that the traction control and ABS lights are on.” And anybody who's worked as a mechanic or has owned a GM car knows that GM can't build a wheel bearing to save their life; generally, all the tech has to do is figure out which one, and after that it's essentially money in the bank. Unless it's a Saturn Vue, but I digress.

This one was much more interesting.

Trouble codes are defined by the automaker and the SAE, and they have a prefix for what type of system is affected. P codes are for powertrain, C codes are for chassis, B codes are for body, and U codes are for communication.

Most of the time, when we diagnose a car, there are a few codes in it relating to the problem. Typically two or three (of course, this varies by type of problem, but, let's just say that seeing more than a dozen codes is generally a BAD THING).

Somewhere I have a document with all the codes this poor Impala had, but it would bore you to list them all out. Suffice to say there were a lot.

Sometimes when you get something with a boatload of codes, the best thing to do is document them all, clear them all, and then see what comes back. And it's well known in the industry that you ignore communications codes unless there's a problem with that system [I'll get into the reason for that at the end of the blog post].

I did that.

Eventually, on a test drive, the car did act up. It turned on the lights that the customer said that it did, and it also went into limp mode in the transmission. Limp mode is basically the car saying something went wrong and I don't know what to do, so I'll default to one simple thing. Like that Silverado with the bad transmission range sensor that indicated 2 on the dashboard.

In the case of automatic transmissions, that's usually a default gear, or if it's got more than one, maximum line pressure. Shifts like a sports car.

Each module can generally tell you who it can't talk to. Of course, in some cases that's not terribly useful; the Driver's Door Module (DDM) doesn't care what the ABS module is doing, so it won't set a code if it can't talk to it, because why would it want to?

Here's the network topology map for the Impala.

What I found was that all the high speed modules could talk to each other. All the low speed modules could talk to each other. But ne'er the twain shall meet. . . .

The warning lights were because the IPC asked the ABS module how things were going (state of health check), and all it got back was crickets. It had to assume that the ABS module had fled the country and wouldn't work.

Meanwhile, the TCM asked the IPC how fast the car was going (vehicle speed sensor reports first to the IPC). The IPC didn't respond, so the TCM decided that something had gone terribly wrong and went to backup strategy.

What we had were the two separate networks talking amongst themselves, and the guy who was supposed to be relaying messages (the BCM) was asleep on the job.

One other tipoff? And this one is going to seem counterintutive to y'all, but it's generally the case: the BCM had no codes.

“Now wait,” I can hear you all telling me. “You implied somewhere up in your rambling that computers are, like, self-diagnostic and self-aware.”

In some cases, yes. But in the case of networks, they're not. And when you think about that, it really makes sense. The BCM knows that it tried to send the message, and that's all it knows. Every other computer on the car knows damn well that there was no message, but how could the BCM know? It's not at the other end of the network, asking itself how it's doing. Instead, you've got the TCM saying “how fast are we going?”

And the BCM says “LA LA LA LA EVERYTHING IS FINE.”

The IPC asks “Hey, ABS, you there?”

The BCM says “MY HOVERCRAFT IS FULL OF EELS.”


On cars, computer networks are bad at taking turns.

They've got one or two wires (depends on the network), and everybody who's on that network has to talk on it. Sort of like a party line, if you're old enough to remember those.

This is why you ignore communications codes unless there's a problem. Let me give you a bit of an example:

RADIO: Hey, I just wanted to let you guys know—

IPC: YOUR SPEED IS ONE MILE PER HOUR.

RADIO: That's great. I just—

IPC: YOUR SPEED IS TWO MILES PER HOUR.

RADIO: Okay, that's important, but—

IPC: YOUR SPEED IS THREE MILES PER HOUR

RADIO: Are you even—

IPC: YOUR SPEED IS FOUR MILES PER HOUR

RADIO: Dammit, IPC, all I need to say is—

IPC: YOUR SPEED IS FIVE MILES PER HOUR

And so on.

The radio never got a chance to talk, and so maybe the BCM set a code for “Where's the radio?” but it's really there, and it's really okay, it just got drowned out by the IPC.


Networks communicate with data packets, and those have a certain voltage. For example, you might have a network where it's a square wave signal that's no less than five volts. If it is less, the computer can't see it, and if there's something else on that line that generates more than five volts, you're never going to see the underlying message.

To put it simply, if you hook direct battery power (nominally 12v) up to a CAN bus, all you're gonna see is that 12v signal. All the modules can be communicating just fine, but they're overwhelmed by that 12v signal. And if you encoded it somehow—let's say that you've got the wire in your hand, and you're tapping it really fast on the battery in binary, you can cover the normal signal on the car and fool it into reading yours.

While it might be possible to steal a car that way (I legit have no idea) the important thing to remember is that higher voltage signals (louder) win over lower voltage signals (quieter).

In our example above, the IPC wins over the radio. Whatever the IPC has to say is more important than the radio, anyways. Nobody cares what the radio wants.

And there's in fact a whole hierarchy on the network(s). Engine controls generally 'win' over other, less-important modules. While this is likely an oversimplification, the PCM shouts, the BCM talks in a normal voice, and the radio whispers.

The airbag module is Fluttershy.


Source (YouTube link)

One health check at key-on. The airbag module checks all its circuits, and then it tells the BCM and/or IPC that everything is okay, and then it just sits in its little corner all by itself and any messages it sends are barely audible.

Until you crash, that is.

If that happens, the airbag module has a gorram megaphone, and for one shining moment, it is absolutely the loudest module on the entire network. When it becomes active, there is nothing that takes a higher priority than it, and if that wasn't enough, it doesn't even need the vehicle's electrical system to work. If the battery is gone, that makes no difference to it; the airbag module is the entire vehicle, and it goes out in a blaze of glory.

And I do mean goes out; after the airbag module has been activated, it must be replaced. There is no consideration of circuit protection for that little guy. It has one job, and it kills itself doing it.


Give some love to that little module. It's quiet and introverted, but when it comes time to save your sorry butt, it's got this.


Source (YouTube Link)

Comments ( 76 )

I now want to see a story of the ponified innards of a modern automobile, especially after that bit about the heroics of Airbagshy.

when it comes time to save your sorry butt

RELATED:

Always wear seatbelts. The airbag module can't help you if you don't.

4681264

That video reminds everyone only dummies don't wear seat belts. I just shake my head at the idiots who don't buckle up.

That was a LOT more interesting than I expected...

I guess because my dad and I were recently replacing his alternator, and electricity arced. None of the accessories worked after that. Turns out, we just burned out some fuse wire. But that was a pain to figure out.

Admiral, you just posted 3000 words about carburetors and on-board computers. You've crafted entire universes that are shorter than this. :rainbowderp:

Not that I'm complaining, mind, but . . .

VAC RSVR W CHK VLV

Vacuum reservoir with check valve. Pft. 2ez get rekt.

the computer is so dumb it doesn't know.

lol reminds me of my LeBaron. I had it for years with no MIL, though the bulb worked. I thought one day I would scan it for shits n gigs. It had a code for egr solenoid.

and then as a father-son bonding project, they installed a rebuilt engine in it. And when they got done everything was perfect.
LOL.

LOL.

when I unplugged all the wires, I also found this:

Did they seriously ground those ground wires to a plastic lug? Holy shit. Now that I've never seen.

And this brings us to the Impala.

*shivers* Oh god, I fucking hate those cars so much. LITERALLY the way the car is started is the ignition switch tells the BCM, BCM tells ABS, ABS tells TCM, TCM tells PCM. In that order, and if there's a network problem or a dead module, you don't get to start the car. The DUMBEST thing gm ever did, and you know they've done some dumb shit.

4681264 Look at those dummies fly! I had a customer once, we went together for a test drive, when I buckled up she scoffed and said 'I never buckle up.' I asked why. Because 'it's safer to jump out of a moving vehicle before the crash,' she said. :facehoof:

Also:

4681262

I now want to see a story of the ponified innards of a modern automobile, especially after that bit about the heroics of Airbagshy.

It's probably something I could do. Whether I should is a whole different matter.

4681293

That video reminds everyone only dummies don't wear seat belts. I just shake my head at the idiots who don't buckle up.

I know somebody who survived only because he wasn't wearing a seatbelt.

Having said that, I also know someone (me) who got the trip to the hospital on a backboard treatment because he was an idiot and didn't wear a seat belt, figuring "I'm in a snowplow truck; what could possibly go wrong?"

The good news is that I survived and learned a valuable lesson. City buses beat plow trucks every time.

scontent-ort2-2.xx.fbcdn.net/v/t1.0-9/168778_1709950823186_1014698_n.jpg?oh=d0514425b4619d6f3d6b441b14da8031&oe=5A4340DE

4681294

That was a LOT more interesting than I expected...

:heart:

I do what I can.

I guess because my dad and I were recently replacing his alternator, and electricity arced. None of the accessories worked after that. Turns out, we just burned out some fuse wire. But that was a pain to figure out.

When the pixies get out, it's anybody's guess what's going to happen. You were lucky.

I got a truck cheap once because after the former owner had burned out the fuse wire, he replaced it with thicker wire . . . without fixing the underlying problem first. The next thing to go was the ignition switch, and it started a fire when it failed.

Now, I know some of you are going to grumble about the good old days and how simple things were back then.

That you recognise this certainly makes things easier.

I'm not old-school enough to be that familiar with carburetors, to be honest.

When the hell did carburetors become old-school?

Sort of like a party line, if you're old enough to remember those.

:ajbemused:

Also, airbagshy for the win.

God, I feel old.

In other news, I was fortunate enough to witness a 4 1/2 litre Bentley power through our village the other day, attended by a gaggle of of Jags, like teen girls around a football star. Doubtless off to some rally.

God, I feel old, did I mention that?

4681264 Also, bloody hell! Those chaps just popped right out!

4681301

Admiral, you just posted 3000 words about carburetors and on-board computers. You've crafted entire universes that are shorter than this. :rainbowderp:

:rainbowlaugh:
To quote Firefly:

"I'm flawed in that way. I sometimes go on. . . ."

4681264

Doesn't look like that vehicle passes... Though I'm guessing they left the seatbelts off on purpose.

Incidentally, it was funny as hell to watch everyone bail out like that. (Except for that one poor rube who bailed into the side that became the bottom immediately after he bailed.)

4681303
Vacuum reservoir with check valve. Pft. 2ez get rekt.
:derpytongue2:

The only time that entire vacuum diagram made sense to me was when I was in an, um, altered state of mind.

Remember in Futurama when the professor said that it came to him in a dream and then he forgot it in another dream? That is the only thing I can figure for what they did for vacuum hoses on that S-10. Some engineer dropped acid and they gave him a pen and this is what he came up with.

lol reminds me of my LeBaron. I had it for years with no MIL, though the bulb worked. I thought one day I would scan it for shits n gigs. It had a code for egr solenoid.

In the 88 S-10, the oxygen sensor failed, at around 455mV, and of course the computer thought that was just fine. No matter what it did, the O2 sensor was happily reading 455mV. No problems here, let's go on with life.

Did they seriously ground those ground wires to a plastic lug? Holy shit. Now that I've never seen.

I knew I should have put a disclaimer. I stuck them there for the purpose of the photo; they were hanging free when I found them.

*shivers* Oh god, I fucking hate those cars so much. LITERALLY the way the car is started is the ignition switch tells the BCM, BCM tells ABS, ABS tells TCM, TCM tells PCM. In that order, and if there's a network problem or a dead module, you don't get to start the car. The DUMBEST thing gm ever did, and you know they've done some dumb shit.

Hey!

I own an 02 Impala.

Which only starts when it feels like it.

But seriously, I think we can both agree that Ford's aluminum FPDM + steel frame rail + galvanic corrosion was a true moment of idiocy, right?

4681306

Look at those dummies fly! I had a customer once, we went together for a test drive, when I buckled up she scoffed and said 'I never buckle up.' I asked why. Because 'it's safer to jump out of a moving vehicle before the crash,' she said.

Around here, we see lots of farm trucks. And despite occasional customer protests, I dutifully put a floor mat in each one. Because you know what? Maybe it's not to keep your farm truck clean; maybe it's to keep at least some of the cow shit off my work boots.

I do personally know one person who got thrown clear of the wreckage (so to speak). He got really, really, really lucky. Like winning the lottery lucky. He knows it, and I know it.

Multiple differeing speed busses with millisecond responses and data transfer requests?

Sounds like a 1980s home computer.

Not a PC.

Something that NASA ended up useing without having to rewrite the OS or the core hardware until the early 2000s.

PC fight with themselves all the time. Its purely buisiness.

Dumping 12 volt onto a differential signal wire is bad enough if its only the one side, But with cars demanding ever more electrical luxuries and add ons, there 48 volt power loops being talked about, and thats not including the induction pulses from rapid random vibrating contact shorts?

Because of the pressure spike in the cabin caused by the airbag deployment, wouldnt the ABS communicate with teh door to tell it to crank the window open to allow pressure to vent or have they added blow vents for that in more recent vehicles?

Im suprised at the electronics dates. We still had distributor caps with weights and vaccuum only in the UK in the 90s. Then the family switched to diesel, and Unc is driving a 2003 VW Skoda diesel that Im pretty sure uses the tried and tested mechanical analog injection pump. that is, given my understanding of VWs emmisions screw up, they couldnt get the digital computer to do a better job.

I wonder how complex the computer would have to be with a catalytic turbogenerator range extender, non lithium small battery pack, and hub electric motors. Best I can come up with at this time. Oh dear, got distracted reading up on the last 40 years history of 10kW up microturbines which really aint designed for putting in vehicles. I seem to remember trying to think of a cross flow 3D printed turbine compressor exchanger in the 80s, but I hadnt seen any actual tech then so very likely it would only work in extreme laboratory conditions, if at all.

Will be intresting to see how things go with 3D laser sintering for advanced materials for turbine tech etc.:twilightsheepish:

4681318

When the hell did carburetors become old-school?

In the US, in automobiles, in 1989 (IIRC), which was the last year of production of GM's 292 in a light or medium duty vehicle.

In the US, OBD-II has been the mandatory standard since 1996. That's over 20 years.

Also, airbagshy for the win.

:heart:

In other news, I was fortunate enough to witness a 4 1/2 litre Bentley power through our village the other day, attended by a gaggle of of Jags, like teen girls around a football star. Doubtless off to some rally.

That mental image amuses me.

God, I feel old, did I mention that?

Well, if it's any consolation, I do remember party lines. And I have worked on carbs before, at least enough to know that they're mystery boxes made by Satan.

Also, bloody hell! Those chaps just popped right out!

The first guy out got the best flight time. I wouldn't want to bet on his chances of survival, except that he probably did better than the guy the truck rolled over.

4681320

Doesn't look like that vehicle passes... Though I'm guessing they left the seatbelts off on purpose.

Yeah, I'm assuming they did that test knowing full well what would happen.

Incidentally, it was funny as hell to watch everyone bail out like that. (Except for that one poor rube who bailed into the side that became the bottom immediately after he bailed.)

The first guy out got the most airtime, and consequently the most time to regret his life choices before gravity played its cruel hand.

4681262

SECONDED.

~Skeeter The Lurker

4681311

DOIT.PALP

~Skeeter The Lurker

And I have worked on carbs before, at least enough to know that they're mystery boxes made by Satan.

:rainbowlaugh:

4681327

PC fight with themselves all the time. Its purely buisiness.

Yeah, it is that.

Dumping 12 volt onto a differential signal wire is bad enough if its only the one side, But with cars demanding ever more electrical luxuries and add ons, there 48 volt power loops being talked about, and thats not including the induction pulses from rapid random vibrating contact shorts?

IIRC, GDI cars can kick over 100V on the injectors, and they use the inductive kick on one to power the next. And of course that'd got nothing on coils, which can hit 40kV or more, albeit very briefly. Ford, I think, runs >48V on their FICM on the 6.0. Granted, the early ones liked to melt themselves internally . . .

There's been talk of running cars on 48V for a while, but thus far it hasn't been done. They've managed to get more out of batteries instead.

Because of the pressure spike in the cabin caused by the airbag deployment, wouldn't the ABS communicate with the door to tell it to crank the window open to allow pressure to vent or have they added blow vents for that in more recent vehicles?

I don't think it's enough of a pressure spike to matter. Interestingly, though, there are vehicles now that have one-time-use clips on A-pillar covers to avoid turning them into projectiles when the side curtain airbags go off, and I've also seen dash-mounted things that have tethers for the same reason.

Im suprised at the electronics dates. We still had distributor caps with weights and vaccuum only in the UK in the 90s. Then the family switched to diesel, and Unc is driving a 2003 VW Skoda diesel that Im pretty sure uses the tried and tested mechanical analog injection pump. that is, given my understanding of VWs emmisions screw up, they couldnt get the digital computer to do a better job.

Diesels lagged behind in the US as well, because we had different laws on them. It wasn't until about 2007 that we got serious about diesel emissions (which, in the US, was a small part of the consumer market), and then we got low-sulphur fuel and particulate traps and everything that went with that. My 88 Suburban is a mechanically-injected non-turbo 6.2L, and the PCM can only control the EGR valve.

I wonder how complex the computer would have to be with a catalytic turbogenerator range extender, non lithium small battery pack, and hub electric motors.

Well, Toyota's been doing it (essentially) with the Prius since the early 2000s. And honestly, compared to things like GDI, VVT, Throttle-By-Wire, and Fiat's Multi-Air system, the Prius is comparatively simple.

4681315
People underestimate how much a city bus weighs, especially if it's got lots of passengers.

Dan

4681318
Carburetors and choke valves are only used in chainsaws and weedwackers and lawnmowers and snowblowers nowadays. Cars haven't used them for 20 years at least.

Choke valves really don't like me. Whenever I help my dad out with chainsawing fallen wood or clearing the driveway in winter, off the top of my head, I can only recall one time when I got them to start on the first try.

4681341

DOIT.PALP

So basically, we're talking a story that at best a dozen people would understand and appreciate?

Eh, it's not like I haven't done weirder things.

4681347
It's true and you know it.

repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/07/dc/51/large/0900c1528007dc51.gif
That's a diagram of a Rochester Monojet. The simple one, without electronic controls, like my '78 Chevy has. Multiply it by four, and add more vacuum hoses and electronics, and you have the abominations that were the last gasp of carbs.

4681321

But seriously, I think we can both agree that Ford's aluminum FPDM + steel frame rail + galvanic corrosion was a true moment of idiocy, right?

Dude they do that ALL the time. They have to be doing it on purpose. The solid-state relays for radiator fans and air suspension are the same way. I remember our old shop van - 92 E150 - had the airbag light on for years. One day I felt like diagnosing it. It had a specific code for crash sensor ground wire. Guess what? The side crash sensor on the side of the frame was designed to take its ground via a steel finger that touches the frame. Not a ground lug. A little metal tab that just connects via springy tension. Rusted frame? No ground.

I chopped the wire and grounded it properly.

4681349

People underestimate how much a city bus weighs, especially if it's got lots of passengers.

It weighs enough to stop a 3/4 ton Chevy dead in its tracks. In the process, it can demolish the entire right side of the truck, and rip the plow loose with enough force that it winds up in front of the bus and two lanes over.

Said bus might only be left with a little blue scrape mark along its side.

4681350

Carburetors and choke valves are only used in chainsaws and weedwackers and lawnmowers and snowblowers nowadays.

And as a professional mechanic, I am thankful for that.

4681359
OIder GM TBI systems with the one-wire O2 sensors. Ground braids on those corroded all the time. Usually not a problem, but sometimes they'd cause the O2 voltage to bias, and the computer would misinterpret it, and make the fuel mixture really, really lean. They'd never set a code, of course.

Even the newer ones, critical ground for the TAC; half the time, it's sketchy or completely broken inside the insulation.

And what's up with their hood strap? Ground the hood, but why?

Speaking of weird grounds, what was up with Neons and their strut ground strap that's always, always broken?

And since we're ranting about electrical problems, if you're not familiar with the system, pull the wiring diagrams for the starter on a 99 Olds Aurora. A sixty amp megafuse to the ignition switch! And then look at the start relay, and think to yourself if there might have been a way to use the exact same components they used without running 60A through the ignition switch.

4681352 Who cares?! Flutterbag! This must be Written! Perhaps Twilight Sparkplug is the new part in town, muttering about Nightmare Sunroof or something...

4681366

Speaking of weird grounds, what was up with Neons and their strut ground strap that's always, always broken?

LOL they ARE always broken! They're not even good! They just like clip under that big circular plastic hole plug. Funky ground wires? How about Jeep Liberty fuel filters - they're PLASTIC and they have a ground strap. (Incidentally, most parts stores and like Mitchell don't think it has an external fuel filter. I always have to give the parts guys the part number directly...)
As for the Aurora, that weird ass shit might be a carry-over from the old-fangled GMs with the ignition switch on the bottom of the steering column? You know, because it actually switched the starter, no relays. idk :derpytongue2:

4681360
Well the bus itself depending on make, model and size is a ton or 3... Put a bunch of people on it you can add another ton or 2.
Big heavy object meets smaller object and yeah. It's going to leave a mark... Hopefully you came out ok (and lets be thankful it was a passenger side impact)

Reminds me of the multiswitches I used to deal with at work.

There were two signals off of our downlink from the satellite. Each had half of the possible communications feeds on it (go figure). But since there's two different signals, there's gotta be a way to signal which signal you want connected to your signal-ey equipment.

So they came up with a voltage-gated switching module. One signal connects when the module is receiving 11-15VDC from the equipment (nominally 13VDC) and the other connects anywhere from 15.1-21VDC (the 18VDC signal)

Then some idjit gets the idea that he wants to have two communications setups in the same room, but doesn't want to run a separate line all the way to the switch, so he splits the incoming line.

When both systems were asking for the 13 VDC signal, everything's hunky-dory and happy.

As soon as one kicks into 18VDC mode, the other starts screaming, "WAAAAH! MY SIGNAL IZ GONNNE!!1!111!!"

And then I have to explain to the idjit in charge that we need to open the damn wall up and run another line from the main switch, and yes, that costs.

All I can say is, thank Luna someone axed those things and replaced them with networked signal multiplexing systems.

They can even be wireless!

4681477
3?

Maybe one of the ones built on a cutaway van chassis, used for dial-a-ride...

The 40 foot school bus I drive at work weighs 10 tons empty. About 13-15 when full, depending on if it's the football team or not.
Many city buses weigh more, as transit agencies tend to like stainless steel.
For example, New Flyer's lightest bus starts at 12 tons. And they crow about it having the "lowest curb weight among similar buses tested"

4681360
Oh, and it will tear the front off a full size SUV, without breaking the turn signal lens. There will be creases in the bodywork ten or more feet from impact, and maybe the bottom pane of glass in the forward door section will be shattered... but the door itself will still operate.

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Vacuum reservoir with check valve

That was my guess! I don't know jack about cars, so it's kinda cool to know that I got it right :pinkiehappy:


4681348

A-pillar

That's one of the parts I make at work! Er, used to, anyway. Can't wait for Mustang to start back up. Also, I just looked that up and I was right: we are making car doors!

Limp mode is basically the car saying something went wrong and I don't know what to do, so I'll default to one simple thing

TIL I've been living in perpetual limp mode

Also, because nobody else has said it yet: my nipples explode with delight

4681481
Hey, it could have been worse, it sounds like you only had to deal with two port multiplexing and no band-stacking.

In 4 port multiplexing to address ports 3 and 4 they added a 22Khz tone to the mix, so that 13v+0khz is port 1, 18V+0Khz is port 2, 13+22Khz is port 3 and 18V+22Khz is port 4.

For band-stacking you have two feed on each port one at the standard 950-1450Mhz and another at 1550-2150Mhz. This becomes a problem when trying to run this on older cable. Some older cable won't pass the higher frequency signal or will but at greatly a reduced strength.

Instead, you've got the TCM saying “how fast are we going?”
And the BCM says “LA LA LA LA EVERYTHING IS FINE.”
The IPC asks “Hey, ABS, you there?”
The BCM says “MY HOVERCRAFT IS FULL OF EELS.”

RADIO: Hey, I just wanted to let you guys know—
IPC: YOUR SPEED IS ONE MILE PER HOUR.
RADIO: That's great. I just—
IPC: YOUR SPEED IS TWO MILES PER HOUR.
RADIO: Okay, that's important, but—
IPC: YOUR SPEED IS THREE MILES PER HOUR
RADIO: Are you even—
IPC: YOUR SPEED IS FOUR MILES PER HOUR
RADIO: Dammit, IPC, all I need to say is—
IPC: YOUR SPEED IS FIVE MILES PER HOUR

One health check at key-on. The airbag module checks all its circuits, and then it tells the BCM and/or IPC that everything is okay, and then it just sits in its little corner all by itself and any messages it sends are barely audible.
Until you crash, that is.
If that happens, the airbag module has a gorram megaphone, and for one shining moment, it is absolutely the loudest module on the entire network. When it becomes active, there is nothing that takes a higher priority than it, and if that wasn't enough, it doesn't even need the vehicle's electrical system to work. If the battery is gone, that makes no difference to it; the airbag module is the entire vehicle, and it goes out in a blaze of glory.
And I do mean goes out; after the airbag module has been activated, it must be replaced. There is no consideration of circuit protection for that little guy. It has one job, and it kills itself doing it.

Give some love to that little module. It's quiet and introverted, but when it comes time to save your sorry butt, it's got this.

This is why I enjoy reading your auto mechanic blogs.

We're not going to talk about the carb on the '84 except to say that it did stuff.

. . . Well, you're not wrong.

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Oh, we went all the way up to 5 ports, and stacked THREE bands with a 250-750mHz Diseqc converter to kick the lower frequencies up where the equipment could read 'em when needed. I was keeping my example simple. lol

:twilightoops:

Sounds to me like you were a coworker :rainbowwild:

Now it's all about the 2.1mHz FSK signal and moca nodes and the integrity of the phy mesh and all that lovely gobbledygook.

4681262 Thirded! I mean, Rainbow Dash is an obvious one, probably Applejack as well (brakes). But what about Rarity? Is she the heated leather seats module, or is that Spike? And am I a bad person for wanting Bulk Biceps to be the fuel injection module?

jxj

Found this one in particular really interesting. I'm specializing in Mechatronics and want to do a Masters in this area as well (I actually submitted my application today) so it was interesting to see how the computer network for a car is set up (do you happen to have a larger pic of the impalla network? It was kind of small).
So they run different voltage signals on the same bus? That's really clever, I didn't think of that.

4681567 lol I'm glad you got it!

I could only wish there was a "make it work anyway" diagnostic that would let the wretched thing function well enough that you could trace the problem... Except I know some fool would use that instead of fixing their vehicle.

4681433

Who cares?! Flutterbag! This must be Written! Perhaps Twilight Sparkplug is the new part in town, muttering about Nightmare Sunroof or something...

Alright, Twilight Sparkleplug is a worthwhile pun (yes, I've known mechanics who do call them 'sparkleplugs'). I was thinking I'd have her be the BCM, but an Ignition Control Module might work . . . .

4681476

How about Jeep Liberty fuel filters - they're PLASTIC and they have a ground strap. (Incidentally, most parts stores and like Mitchell don't think it has an external fuel filter. I always have to give the parts guys the part number directly...)

As I recall, the older minivans did, too. Like 96-2006 models, the ones that came with the hoses to the fuel pump. I think that there's at least one GM vehicle that has a plastic fuel filter and a ground strap, as well.

As for the Aurora, that weird ass shit might be a carry-over from the old-fangled GMs with the ignition switch on the bottom of the steering column? You know, because it actually switched the starter, no relays. idk :derpytongue2:

That's what I'd figure. They just sort of did it the old fashioned way.

But here's the weird thing--and I can't remember if I put this in the blog post. The yellow wire on the ignition switch does two things: it provides power to the crank relay pull-in coil through a ten amp fuse. Which is reasonable. And it's also the main power feed to that same relay. Like, WTF GM? All you had to do was not run 60 amps through the ignition switch, and you wouldn't have had a problem, and you ALREADY DESIGNED IT WITH A RELAY.

4681477

Big heavy object meets smaller object and yeah. It's going to leave a mark... Hopefully you came out ok (and lets be thankful it was a passenger side impact)

Well, I was on the passenger side. :derpytongue: Luckily, I've got a thick skull.

4681481

Reminds me of the multiswitches I used to deal with at work.

There were two signals off of our downlink from the satellite. Each had half of the possible communications feeds on it (go figure). But since there's two different signals, there's gotta be a way to signal which signal you want connected to your signal-ey equipment.

So they came up with a voltage-gated switching module. One signal connects when the module is receiving 11-15VDC from the equipment (nominally 13VDC) and the other connects anywhere from 15.1-21VDC (the 18VDC signal)

Then some idjit gets the idea that he wants to have two communications setups in the same room, but doesn't want to run a separate line all the way to the switch, so he splits the incoming line.

When both systems were asking for the 13 VDC signal, everything's hunky-dory and happy.

As soon as one kicks into 18VDC mode, the other starts screaming, "WAAAAH! MY SIGNAL IZ GONNNE!!1!111!!"

Like, how could he have not seen that coming. A bigger signal is going to blind the smaller one every time. I've run into that in car networks, where you have some amount of the 12v battery power leaking into the less-than-12v data lines, and every time that happens, the network unsurprisingly fails. Sometimes with an oscilloscope, you can sort of make out that there is communication going on--or trying to--but of course the computers on the car aren't meant to try and sort their signal out of a 12v signal laid overtop of it.

Incidentally, those are about the worst to track down, because the communications wires are run in bundles with all the other wires, and the voltage leak could be anywhere. The last one I did, I was able to isolate it to a relatively short section of line. The bad news was that it was in the harness that has a junction right by the transmission . . . I couldn't find a picture, but anyone who's worked on late 90s/early 2000s Caravans would know exactly what harness I was talking about. It was basically the junction point for all the wires, and cleverly located where it would fill with leaking oil and transmission fluid, and could rub on the road, as well.

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Many city buses weigh more, as transit agencies tend to like stainless steel.
For example, New Flyer's lightest bus starts at 12 tons. And they crow about it having the "lowest curb weight among similar buses tested"

I don't know what kind Kalamazoo had, but I bet they were heavy. Basically these:
media.mlive.com/kzgazette_impact/photo/kalamazoo-metro-transit-802370ecb4d5301a.jpg

Oh, and it will tear the front off a full size SUV, without breaking the turn signal lens. There will be creases in the bodywork ten or more feet from impact, and maybe the bottom pane of glass in the forward door section will be shattered... but the door itself will still operate.

One of the Kalamazoo city buses recently withstood a headon impact with a Pontiac . . . going over 100mph. The bus driver was badly injured, but from what I know, there was little to no intrusion into the passenger seating area.

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