MECHANIC: What I got for Christmas at the Shop (part 2) · 2:50am January 22nd
This is a part two! It's gonna be shorter than the first one, 'cause neither the discovery nor the repair took as long. Before you get started, though:
A quick summary for those of you who don't remember the last blog post: Explorer got towed in and when I went to move it, it would start and stall. It did not like to turn left but turned right okay, and the longer I tried to get it to move the worse it got, culminating in the hazard flasher switch engaging the starter. The customer had observed that the battery light was on, thought the remote starter was to blame, and uninstalled it. He left a wire loom loose, it got caught in the steering shaft and pulled the rest of the harness in with it, breaking and/or shorting dozens of critical wires. I spent about fourteen hours fixing that mess, but I got it running again and everything worked, much to my amazement.
Well, except the alternator. That still didn't work.
Back in Ye Olde Days, alternators were dumb (in Ye Older Days, they were generators!). The pulley spun and electricity was made, some regulators made sure it wasn't too much (since the faster you spun the pulley, the more electricity it made), and that was what you got.
While generators happily made electricity as long as you spun the pulley, alternators needed some electricity to get things going. That's not really a problem; the car's got a battery and it's full of angry pixies electricity, so some of it can go to the alternator, especially since lots more goes out than what's put in. And that system was fine for decades, until automakers had picked all the low-hanging fruit when it came to improving fuel economy and they had to start getting creative.
While this is oversimplified, since alternators need electricity to make electricity, if you turn off the electricity to the alternator, you reduce the load on the engine when you don't need to make any. Like if you imagine a truck has a 140 amp alternator on it to handle every conceivable electrical load on the truck plus some to recharge the battery plus some in reserve, that's great, but if the truck is normally only using 70 amps, half of the energy you're using to create electricity is just wasted. You can't put more in the battery than it wants or else the pixies will get really angry and that's bad.
So the computer controlled alternator was born. Ford was the first (AFAIK) to commonly use them, and in the early days of their usage aftermarket remanufacturers didn't know how to build them. If you installed an aftermarket alternator in a late-model Ford, odds were it wasn't going to work; the PCM would tell it to do something, it'd get nonsense in response, and the PCM would just shut it off and set a code saying "I don't know what this guy is doing."
Thus it was with this Explorer.
Before I tell you what kind of codes it set, I'm gonna give you a quick overview of how the computer controlled alternator works—well, the parts we care about for this blog. First off, Ford still calls it a generator even though it isn't.
The PCM send a signal down the GEN-COM (generator command) circuit, basically telling it how many amps it wants.* The alternator sends a signal back on the GEN-MON (generator monitor) circuit, saying that it did what was told. Some cars have a current sensor near the battery (usually on the negative cable) which can also be used to monitor loads; I don't believe this Explorer did.
So basically it goes like this.
GEN-COM: "Hey, give me fifty amps."
GEN-MON: "Sure thing, boss. Here you go."
I had two codes, and I can't tell you what they were, since I forgot to write them down. One was the generic "I told the alternator to do a thing and it didn't do it" code which usually means that the alternator is bad—it didn't do it because it can't do it.
The other was a circuit code.
Tests were fairly straightforward, although instead of following Ford's flowchart, I instead chose to use Identifix's simplified flowchart. It passed the first few tests: the GEN-CON had the right voltage measured at the alternator, the fuse was good, and the next test was to see if the GEN-MON was actually sending a signal to the PCM.
On these, the PCM is under the wiper cowl—the wiper cowl is the black plastic thing you have that sits under the wiper blades and probably has a grille in it which lets air into the HVAC system. You've got to pull the wiper arms off to get to it (some Ford models, you can pry the cowl up far enough to access the PCM without actually removing the cowl).
I'd done that and was in the process of backprobing the PCM connection and not having any luck. None of the probes I had would make contact. We do have wire-piercing probes, but those aren't ideal for automotive work: when you make a hole in the insulation, you also potentially create a future corrosion problem, since now moisture can get in.
It was late in the day, my manager got impatient, and decide we'd just put on an alternator and see what happened.
Now, on an Explorer like this one, there are two ways to put on the alternator. The first is what Ford suggests, which is take off the airbox, upper radiator hose, and cooling fans, then remove the alternator from the top. The other way is to evacuate the A/C system, remove the A/C compressor, and pull the alternator out the bottom.
I opted to do it Ford's way, and as I was installing the new alternator my manager commented that the other tech had done the last one the other way and it had only taken him an hour and a half to swap the alternator [it only took me 1:15 to do it the way I did; evacuating and recharging the AC system takes at least fifteen extra minutes, maybe more depending on what the temperature is and how deeply buried the AC machine currently is].
Anyway, with the shiny new alternator installed, the Explorer fired right up and promptly set the same two codes.
The first thing I checked was if I'd remembered to plug the alternator in.
I had.
The next thing I checked was Identifix again, 'cause I remembered seeing a few verified repairs that were wiring problems.
Sure enough, there's a connector right by the fuse box and by golly, the GEN-MON wire was very obviously green. Right up in the connector, and the me of a week before I'd started repairing the under-dash disaster would have thought it was broken too close to the connector to fix; I'd never even get a heat-shrink on it.
But I'd fixed an under-dash wire that was worse, so I boldly pulled that terminal out of the connector, stripped it down to where it was crimped in, soldered in a repair section, and put the smallest heat shrink we had on it.
That still wasn't small enough to make it fit back in, but a sanding wheel in a Dremel fixed that little problem.
This time when I fired it up, the Explorer was happy, the alternator was happy and the PCM was happy with the alternator . . . I took it for a test drive and everything worked as intended.
Is there a moral to this story?
Well, maybe you won't save money doing it yourself. Case in point, I just worked on a Cadillac that had malfunctioning blind spot monitors. The little radars that make the system work are high failure items (understandably; they're in a terrible spot on the vehicle, but that's where they have to be). Corrosion in the wiring is also commonplace; we told the customer that it probably needed radar units and if there was any corrosion we'd have to replace the bumper harness, too. We couldn't tell him any more until we pulled the bumper to see what we saw.
He didn't want to pay to have us do it, so he took it home and did it himself, two brand new GM radars at $400 a pop. He didn't replace the wire harness 'cause he didn't see any corrosion.
On Monday I got to program the new units, and they wouldn't communicate with the scan tool, so we had to pull the bumper to find out why. There wasn't corrosion in the connectors . . . but there was elsewhere in the harness, and the old units hadn't worked 'cause the power wire for them had corroded through. We put the wire harness on and that fixed it; it probably hadn't needed the radars at all.
I'll admit, the manager and I were biased towards bad radar sensors, 'cause we've seen plenty of them that have failed. But what the customer didn't know was that this is one module where the failure is usually obvious externally; usually there's so much corrosion inside of them that they're all swollen up like a lithium ion battery that's about to pop. I don't know what the units he pulled looked like (I never saw them), but I do know that if I'd been working on that, I'd have done a bit more diagnosis if the units had looked a lot cleaner and less exploded than I expected them to be.
Point is, I don't fault a person for trying to do it themselves and save some money. But if you don't know what you're doing, you might not save any money at all, you might in fact cost yourself hundreds more in unnecessary repairs. Whether it's something that should be obvious (like make sure wires stay out of rotating assemblies) or based on experience (like bad radars usually look exploded), a professional has probably seen it before and will perform extra steps to make sure. Two Fridays ago, I was on my back under a Silverado testing if an upstream oxygen sensor was bad and I unplugged it and even though it was dripping salty icewater on me, I took the time to zip-tie the wire up because it could catch on the driveshaft and a minute of extra work under that stupid truck could save me hours of repair time later.**
Outro!
*AFAIK, this is commonly done by simply turning the alternator on and off very quickly, what's known as duty-cycling. If you want full output, you have the alternator on a hundred percent of the time. If you want half output, you have the alternator on half the time, etc.
By the way this vehicle is wired, this happens inside the alternator, presumably by some solid state 'relay' turning itself on and off for a set period of time.
**In that case, it turned out that the oxygen sensor wasn't the problem.
I like how the PWM power control used by the computer just duplicates what the alternator power relays used to do electromechanically. They used voltage and current sensing when working correctly and when the relay terminals burnt out cos of switching off high current flows, not working correctly.
Strange thing is that although its called an alternator, and generated 3 phase electricity, certainly the older versions immediately go into a full wave rectifier, trying to turn it into DC.
And now we have 3 phase Fast chargers for electric cars.
So a 200 Amp 24 volt Alternator would generate the 6 HP that Porches first electric race car needed for cruising at 30 mph, and the other 200 amp for acceleration for a few seconds could easily be supplied by a half decent normal car battery? thats a lot of, Extras, on a modern rig.
Its extremely impressive what they can do with electronics tehse days. Last year they announced kilowatt microwave solid state units for ovens, and in the last few months other researches have claimed some design that can run at 500 C. So maybe we will be seeing long duration Venusian rovers that are not just a magnetic slinky.
I wonder if theres Any car manufactuer looking to use L4 for its OS, and how they would access it to check theings when its so paranoid about outside attacks that the US Airforce have been trialing it in an AI Blackhawk?
Pity Mythbusters didnt do a, How far can you wind a car on its starter motor, to get a comparison for electric vehicle performance, espeically in temperature extremes?
5764647
I remember a Russian YouTube video where they removed the engine from a car and reseated the starter motor so they could drive powered only by the starter, but I can't find it anymore
5764663
Can't say for sure that it was them, but that sounds like the sort of shenanigans that Garage 54 would get up to with an old Lada.
Ahhh, the good old "Do It Yourself" special...
(Video only related by title)
5764663
One farmer where I used to live didnt even bother doing that. When his clutch failed, he just stalled teh car on hill outside my house when he dropped me off, then started teh car as usual, in gear, uphill and the engine fired up within 30 foot or so. If it hadnt, it was only a hundred foot to the level road at the top of the hill, and a quarter mile or so to the farm. Ten minutes of cranking wouldve seen him home.
As I sit here typing, charging the battery of the loader that definitely had feed plugging the fuel intake. I wonder how to flush the fuel tank on this thing...
5764698 In college, I had a 76 Subaru 4wd wagon with such a teeny engine that when my battery went out in summer, I let it go for about two weeks. I could coast down the hill from the apartment and pop the clutch to start it, and from my parking space at the University, I could roll *backwards* and start it that way. Figured it took about a foot of elevation to start, but the wife made me get a battery anyway.
5764647
It's probably a simpler system overall, and can do stuff that the old-fashioned systems couldn't do. On the down side, it's probably not quite as robust as the older stuff, but then again the cars we're replacing alternators on usually have more than 150k on them (280k km or thereabouts), which isn't as long as a lot of old engines lasted.
There's also a lot more electrical loads on a modern car than there were on the old ones. I don't know how many HP an alternator would make if you turned it into a drive unit, but I do know that some mild hybrids do use the alternator to 'drive' the engine sometimes.
It'd really depend on the starter; most modern ones are gear-reduction and not designed for long duty cycles. Some of the older ones were huge and could easily drive a car for a while; on two occasions I started my old farm truck in gear ('cause the clutch linkage broke), once on an uphill grade. After the second time I started carrying a spare clutch linkage in the glove box.
5764663
I agree with 5764674, that sounds like something that YouTube channel would have done.
It would depend on what starter motor you had, how heavy the vehicle was, etc., but I can tell you from personal experience that I was able to start a late 70s Chevy pickup in gear with the starter after the clutch linkage broke. The starter was able to get the engine turning over fast enough to let the engine run while also pulling the truck along with it.
One time was on an uphill grade, and I had to make a left turn.
5764678
Depending on how much I feel like making fun of some of our customers over the next couple weeks--or if we make any interesting discoveries--we've currently got two vehicles in the shop that the customer attempted to fix themselves, and then towed in when they couldn't.
Both are partially disassembled, with some or most of their parts scattered about inside them.
For one of them (I haven't looked at the other yet), I don't even know what they were trying to fix. Just what they replaced thinking it was the problem.
5764698
Our tech director at one theatre did that; he'd park his Ford at the top of the loading dock and when it was time to go, he'd roll it down to the bottom and pop the clutch to get it going, then back it out.
It's not the best solution, but it's a solution.
5764729
I won't say it's the easy way, but the right way is probably pull the tank, remove the fuel sending unit, and then clean out the inside through that access point. Depending on the design, that might not be an easy project. . . .
If the feed will float on water, and if you can drain the tank, you might be able to empty it, then fill it with water and skim off all the bad stuff, or at least all of it that'll float.
The other option is prepare to replace a lot of fuel filters on it; eventually everything that can fit through the fuel line will go through it. Or something will clog the fuel line, which gives you a different problem. . . .
5764746
I didn't have a S.O. to convince me to fix some of the problems on my old truck. One of the things it did was stall on highway exit ramps, pretty much every time. I'd just let it coast down to about thirty, pop the clutch, and it restarted, so it wasn't that big a deal.
When you've got some momentum behind the car, it really doesn't take much to get the engine to start--if it's going to.
5765414
The plot thickens... after disconnecting fuel line and running a temporary one into a bucket of diesel, the engine would only try to run after I raised the bucket above it. Further, despite a fresh battery and jumper cables to a running tractor, it would only run for 30 seconds before dying and with the battery idiot light on. So... electrical system and fuel pump problems, possibly the same root cause if the pump is electric.
The fuel tank is all but part of the frame, thus it would need to be hosed out in place. Experience tells me not all the stuff floats on top, too.
In more mundane things, the flex pipe in my car's exhaust broke last week and I hacked in a replacement. I think there's too many holes where I welded the piece in, but I bought myself some time to take it to a professional later without gassing myself. Or violating noise ordinances.