noise."MECHANIC: I've got a friend with a Mercedes Benz · 1:04am Jul 15th, 2023
LOL JK anybody who don't dance has a Mercedes they want me to work on ain't no friend of mine.
I think you can already guess what brand of car I'm gonna talk about, and I think y'all know what to do:
It just now occurred to me that I don't even remember what year this stupid thing was, so we're gonna say it was a 2013.
Last week, just before Trotcon, my manager was on vacation and I was in charge. Late on the day on Friday, a guy called who had a Mercedes R230 that chucked its serpentine belt and wanted to know if we'd fix it. He was an out-of-towner, but knew a guy who recommended our services.
If you're not familiar with Mercedes--or German cars in general--they do things their own way which I'm sure make lots of sense to Germans, but not as much to Americans. And I'll give them credit, the Germans figured out standardization of wiring diagrams long before Americans did; if you've ever wondered why your automotive relay terminals are numbered something like 5, 30, 87, 87a, and 88, blame the Germans. I think once they invented electricity, they sat down and figured out a way to notate it, even using tech that hadn't been invented yet (as I recall, they're also the reason car radios are measured in DIN slots). They have their own way of organizing engine codes as well, which we'll be getting to.
Mercedes also identifies engines by chassis number and engine number rather than model and displacement. For those familiar with American cars, it'd be like if you had a 1989 Chevy van with a 5.7L that you instead had a 1989 G with a K. [In the case of GM, if you know which letters in the VIN tell you which things, this is easy to find; Mercedes does it differently.] So that 2013 (I think) R230 with a V6 is, in Mercedes-speak, something like a 251 chassis with a 272 motor.
I do a quick check of our usual suppliers and nobody's got the belt or the water pump (which the customer said it needed) and informed the customer that he might be better off towing it to a Mercedes dealer, or somebody who specialized in German cars. And I thought that was it.
Right before closing, he calls back. He's phoned around, and one of our suppliers (unlucky coincidence!) can get the water pump and belt by Monday, so I hop back on the computer and by golly, maybe they can. I also find that there are two different water pumps for this dumb thing, and how you tell them apart is by engine serial number.
I ordered both.
Come Monday, the car is sitting in our parking lot. My first sense of alarm comes when I look at the badging. They guy said it was a R230, I only had one option when it came to ordering parts, but this thing's got AMG badges out the wazoo. Also says that it's got a 6.8L V8; the catalog didn't give me engine options.
Of course, that's sometimes the case with special editions. Back in the day if you looked up engines for a Ford Taurus, you'd get two options, both 3 liter V sixes. One had dual overhead cams, one was a pushrod engine. If, however, you said that it was a Ford Taurus SHO, you got an entirely different engine option.
Luckily, that wasn't the case for this thing. Someone spent a lot of time and effort to badge it as an AMG, but it wasn't. Maybe that's why he didn't want to take it to the dealer; maybe he knew they'd spot it as a fake in an instant and mock him.
Luckily, I'm not gonna tell anyone.
When I pop the hood open, the belt is indeed missing. The water pump pulley spins by hand and doesn't feel bad; it's probably not why the belt broke. Couple of the idler pulleys are plastic and kinda melted, and as I do further investigation, I notice that the pulley on the front of the air conditioning compressor--and everything else associated with it--is gone.
I'd find them later on the underbody shield.
There's also a bunch of warning lights on, so I pull codes and oh boy did it have a lot. Mercedeses are too smart for their own good; they can set multiple codes for each light bulb on the car. And it did. Along with other things; I won't bore you with a complete list (I didn't write them all down), but in the engine alone, there were ten codes. Cylinder specific misfire code for every cylinder, general misfire, lean on bank 1, lean on bank 2, thermostat stuck open. The engine didn't have the most codes; IIRC that honor went to the front Signal Acquisition Module which had somewhere around 30. It was overdue for some kind of service, the auxiliary battery was missing or defective, and nearly all the forward-facing lights had one or more codes. All the light bulb codes were due to LED replacements being used, or the wrong bulb used for service; we replaced all the easy-to-get-to exterior lights minus the headlight bulbs*.
And here I'll give Mercedes credit, unlike some manufacturers, they figured that light bulbs might burn out over time, and made all of them easy to change. You didn't have to pull the front bumper to change the turn signal bulb, for example. Most of them you didn't even need a tool, just reach in and change it.
Source
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*Since it originally had Xenon HID bulbs which had been replaced with LEDs, we'd have had to replace the bulb and the ignitor for each, probably a few hundred dollars per bulb.
I'd done an AC compressor on one Mercedes before, and it wasn't fun. For starters, you need inverted Torx sockets, and I don't have a huge selection of those. It's kind of in a tight spot and three of the bolts aren't fun to get at, but it's not terrible. I've done worse. Everything down there was a greasy mess, too; as nice as it looked outside, the same couldn't be said for the engine bay.
Also, I couldn't find the high side AC fitting; if I'd known more about Mercedes, I'd have known where they were likely to put it. [I did find it after the work was done; it lives just behind the grille.]
We never did find the engine serial number. I found where it was supposed to be, thanks to the internet, but I don't know how you'd see it with the engine in the vehicle. It didn't matter, when we had the two water pumps side by side, we could see the difference: one of the mounting bosses for an idler pulley was different.
A lot of water pumps have some small bolts and some big bolts; in many engines, the water pump mounts on the front cover. You'll have a few long bolts that go all the way through to the block which do the bulk of the fastening, and a number of smaller ones that keep the gasket tight. This one had four big bolts (which were two different lengths), and seven or eight little ones.
Also most cars use metric fasteners in common sizes and thread pitches. For example, practically every bolt on a Chevy is gonna be M6x1.0, M8x1.25, or M10x1.50. There are some exceptions; they use M12 and M14 bolts on many models and a few other specialty ones for heavy-duty fastening duties (brake bridges, harmonic balancer bolts). Asian manufactures often use fine-thread bolts (M10x1.25, for instance), but either way they're usually even sizes.
All those little bolts on the Mercedes were M7x1.0, and they were hiding a dirty secret.
I usually don't care about bolt size; you put the bolt back in the hole it came from, and you don't have a problem. Thing is, when I took these out, they came out hard and they took threads with them. That'll happen sometimes when you take a steel bolt out of an aluminum component, and all I should have to do is chase the hole with a tap and it'll be good.
Lingo explainer: There are special tools to fix threads and special tools make new ones. Cleaning existing threads is 'chasing' them, making new ones is 'cutting' them. The tool that puts threads in a hole is a tap; the tool that fixes threads in a hole is a thread chaser. You can use a tap as a thread chaser, but you can't use a thread chaser as a tap. If you're putting threads into a rod (i.e., making a bolt), you use a die for that; if you're cleaning a bolt, you also use a chaser. You can use a die to chase threads, but you can't use a chase to cut threads.
As luck would have it, our tap and die set has M7x1.0, and I got all the nasty bits of aluminum out of the bolts and made good, clean threads in the front cover and things went well until I torqued it down. Several of the little M7 bolts spun free before they reached their torque.
What I would find out later is that they were self-tapping bolts, which basically means instead of having a hole with threads in it, you have a special bolt that makes threads as it goes in. Domestic manufacturers use them to hold things that don't weigh much or have to seal, they certainly don't have a stupidly high torque spec.
I suspect that we should have replaced the self-tappers with new bolts and it might have been okay. As it was, there wasn't enough clamping force to keep the gasket from leaking. We don't have a lot of service information for Mercedes since we don't pay for comprehensive European information.
Out of better ideas, I tapped each of the M7 bolts to be M8 bolts. Some Mercedes tech in the future is gonna have a bad time. We had to order a new water pump gasket, which couldn't be got in the aftermarket. Mercedes had one, and it was shockingly cheap ($6.00), especially since it would turn out to be a proper metal gasket instead of the fiber one that came with the aftermarket water pump.
As an aside, while shops that specialize in things know lots of stuff about those things, generalists like us don't. This is the first time I've worked on a R230 and I might never work on another one. On a few occasions where I've called the dealer on something I'm not terribly familiar with, a knowledgeble service person has helped me out. "Oh, you're ordering a water pump? You'll also need new bolts, you can't re-use the old ones." Once upon a time, years ago when I was managing the shop, one of the mechanics was doing a timing belt on a Highlander. He broke the stud that holds the motor mount in place (it was sized with corrosion, nothing he could have done) and when I called the dealer to order one it went like this:
ME: I need a stud for the left motor mount on a Highlander, doing a timing belt and it broke."
DEALER: We've got one, it's a part number X. And the motor mount is part number--"
ME: Don't need the mount, he got the broken stud out of it.
DEALER: . . . How?
I guess they sold a lot of those studs and mounts.
We also used to have a grumpy old man who ran our local parts store. If a part existed, he could find it. I called him up one time and said that I 'needed that coolant fitting that leaks on Chevy trucks,' and a few minutes later I had that coolant fitting.
With the holes tapped to a new size, in part with a home-made bottom tap** and a new gasket from Mercedes, everything torqued down to what my manager determined was a sufficient torque (less than the literal German Spec***), and both a vacuum test and a pressure test done, I refilled it with coolant, started it up, and we were off to the races.
In more ways than one; the engine revved really high on startup (usual goal for an idle is 700-1000RPM, this thing started its idle around 2500 RPM and then grudgingly brought it down to a more sane number.
It warmed up, it didn't leak, and it was done. And if you believe that, just read the following footnotes and then skip right to the end.
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**normal taps are tapered and meant for through holes. A bottom tap isn't, since it needs to cut threads down to the bottom of the hole. I home-made one by cutting the tapered end of a normal tap, and I tapped the hole with a normal tap first, then picked up the last few threads with the home-made one.
***In mechanic lingo, German Spec is "goodentight." Experienced mechanics know what bolts can be tightened to German Specs, and also know to say click click as each is tightened, assuring proper torque.
Somewhere about 2,000 words ago, I mentioned that this car had the Check Engine light on, and that it had lean codes for both sides of the engine, as well as misfire codes for each cylinder. But it ran okay, aside from the high idle . . .
One of the reasons that computerized cars got a reputation for unreliability was because unlike a mechanical-controlled engine, the computer could make corrections. For example, if the fuel mixture is wrong, the computer can add more or take some away until it's in the ideal range again. Of course, eventually things go so far wrong the computer can't do any more to help, and then it 'suddenly' quits. Never mind that the 'check engine' light was on and ignored for thousands or tens of thousands of miles.
FWIW, the check engine light's been on in my van for 60,000 miles (100,000 km).
It learns these corrections and uses them the next time the engine is started--this will become important.
In what I can only assume was a bout of insanity, my manager said that we couldn't give it back to the customer with a high idle and a check engine light and said I should clear the codes, so I did.
On some cars, resetting the check engine light turns it off, clears the codes, and doesn't change the adaptive values. On others, such as this Mercedes, it does both. After all, you'd only clear the light if you'd diagnosed the codes and made the appropriate repairs, right?
Right?
German engineers misunderestimated the American approach to problems.
The good news is that the check engine light isn't on any more, and for what it's worth it also doesn't start with a high idle. In fact, it barely starts at all. If you modulate the throttle, it'll run . . . sort of. It's not very happy about it.
See, whatever went wrong with it, whatever caused all those codes, slowly failed over time. The computer was able to adapt to it. Since it's got lean codes, I know it wasn't getting enough fuel, so it started adding more. There's some allowable variance (usually +/- 10%) before the light comes on, but it can do more than that if it has to. I've seen some domestic cars go up to 70% fuel correction before they give up.
Identifixing the lean codes gives me a path to follow. Dirty air filters, or the housing installed wrong can cause it. The air filters are dirty, our local supplier has them . . . my manager complains that I didn't tell him that they were dirty when I did the inspection for the oil change, and I counter that I usually don't check air filters if you've got to remove a structural brace and a wiper cowl support just to look at them.
It wasn't the air filters.
I didn't think it would be, but that would have been a nice easy repair, wouldn't it have been?
Since this engine is biased lean, it's a good chance that air's getting in where it shouldn't. Or the fuel pressure is low, and it's not injecting the volume it thinks it is. If I'd taken it for a test drive before clearing the codes, I could have gotten an idea which path to follow, but I didn't 'cause I wasn't expecting a courtesy code clearing. Now it runs so badly that any airflow reading is nearly meaningless.
There are other ways to approach this. Some Mechanic Blogs ago, I smoke tested a leaking cylinder to find out where the air was going; you can do the same with an intake. Plug off the intake system upstream of the mass airflow sensor, put smoke in whatever hose is most convenient, and where it comes out . . . well, that's where the problem is.
Source****
Maybe a leaky gasket, maybe a failed o-ring on an injector, or--
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****the description on that image is "We have called to inform you that your sled warranty has expired."
Someone sent me a PM regarding my blog post about VREF failure on an Explorer. They had a similar Explorer and an similar problem and traced around and by golly my blog post saved them some time. In the interests of full disclosure, these are meant for me to vent and for you to be entertained; any use they are in diagnosis or repair is more of a happy accident than an intention. That having been said, I'll take what I can get, and if a blog I wrote about a problem vehicle saved you a lot of time on your own, well, I'm happy to help. If you're just here to thank Celestia you're not a professional mechanic, or just like the cute pony pictures, I'll take that as well 
I bring this up because what I found on this might be useful to one of my readers who owns--or who knows someone who owns--a Mercedes of about this model year with an engine in this family, and I since I didn't think to get more specific information on this car I'm doing y'all a disservice.
Some cars have tumbler flaps and variable-length intake runners and all sorts of tech up in there, and from piecing together reports in the field, sometimes the tumbler flaps fail inside the intake mainifold and one of the consequences is that they rub a hole in the intake manifold. That allows air to get in that the computer doesn't know about, and it makes the engine run lean . . . it probably started as a small hole, and the computer kept making corrections and then I went and cleared the codes.
I still haven't told you about blocking codes, but suffice to say that after the initial engine codes were cleared out, it set a code for the tumbler flaps not working. Despite our best attempts, it left with the check engine light on.
Now you might be asking how we fixed it. We certainly didn't put an intake manifold on it (which is what it needs). Well, my manager had a high-tech solution:
Yes, I'm being serious; he taped over the hole. Which is a good temporary fix; it'll work until it doesn't.
This brings us to the lesson learned. I suppose that there are two lessons to be learned here.
1. I should have told the customer outright that I had no interest whatsoever in working on his Mercedes. Maybe instead of going down the 'difficulty of getting parts' angle, I could have said that we had a lot of work and it would be a week or more before we could even get it in. That discourages impatient people, and most of the time it's true, too. I've told that to a few customers I really don't like in the hopes that they'll go somewhere else . . . and I've told it to many more people when it's actually true. To paraphrase the voicemail message one of my friends had, "I'm either unavailable or actively avoiding you. To find out which, leave a message and see if I call back."
2, Clearing codes without knowing the root cause can turn into a disaster. Sure, now we know (and he knows) what's wrong with his car, but we spent a lot of unplanned time on diagnosis that could have been avoided by knowing up front if he was willing to spend more money to make his car right.
This was a long one . . . I feel like I owe you a relentlessly cute pone or two as an outro.
Yeah but now you know so much more about working on Mercedes and your manager can brag that he has an expert on staff!
His friends all
Drive Porsches
He must make
A-mends...
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Your blog has reinforced that I do not want to be a mechanic of any description, thank Celestia!
5737925
GM calls them "service technicians" because the 12th commandment is
"Thou shalt not be understood.".
the 11th is
"Thou shalt not get caught."
This is the most important
one.
I need a dust filter for a Hoover Max Extract® Pressure Pro,™ Model 60; can he help me with that?
>Yes.
Cuz speed tape is a thing in aviation as well. You tape the non-critical damage and the plane can execute the flight as normal before heading into maintenance, and thus no need to mess up the schedule by getting another plane at the last minute for the flight.
This is the reason why my uncle who is a country mechanic, he does passenger vehicles and some tractors, will not touch VW or many other German models. He doesn’t mind the Japanese stuff.
5737921
Oh Lord! Won't you buy me? A Mercedes -Benz
Oh, what I wouldn't give for a scale that said smol.
At least he had the right fake badging on it.
Not slapping Type R Honda badge on a Kia.
Or a Bentley badge on a base model Chrysler 300.
I’ve seen both of these in person.
Mechanic: Your computer has a lot of codes. I think its easier to tell you what isn't blowing a code. Your floormats are ok, and the windshield washer is full. The rest, however...
5737925 as a computer/network mechanic of a sort, I agree with you. As weird as computers are, cars are worse.
Not sure which car this was, think it was the Ford Taurus, but to replace the headlight bulb you had to stick your bare arm down a steel-blade-lined channel with a flashlight propped on the engine to one-hand disconnect the bulb, pull it out of the blood-greased channel, swear for an hour or two while pulling the bulb out of the socket, break it, rip it out with pliars, put the replacement into the socket, take it out, go back to the parts store to swap it with the right part that the book said was the wrong part but the old guy behind the desk had you use it, which fit into the wire socket perfect but now you had to put your arm back down that steel channel and attach it, then go apply bandages.
Ok, some engineer needs a smacking.
5738009
Coincidentally I'm currently traveling and the headlight burnt out on my VW Sportwagon. I had replaced the other a while back and it came in a pack of two so happened to have a spare. Took like 3 minutes to change it in the hotel parking lot. So VW definitely nailed that.
Money quote of this post.
You're a braver man than I to try and diagnose/repair a Mercedes.
Woona for the outro, best!
Replace parts store with tractor dealer and you have my former boss.
Nothing like finding water pump parts for a 1940s Kelvin T6 marine diesel. Thankfully the OEM is still in business and had the parts.
Yuck, what a nightmare of a car!
Latest bit of fun in the farm shop: Friday afternoon, when loading sand into a dump truck, I had the front left lower 'kingpin' bearing on our JCB loader come out. Near as I can tell, after a bunch of work on the hub a year or two ago, the bolts holding the bearing backed out until they mostly came out and the wheel went cockeyed while I was turning. Fortunately, the machine can still steer, the wheel still spun... so an hour of fiddling around later, a coworker and I got the bucket off, chained the loader arm to a 3-point hitch bracket on our biggest tractor, lifted the front of the loader clear of the ground, and sloooowly towed the thing the mile to the farm's shop.
Now to see if the bolt holes are egged out. I'm hoping I can just chase the threads, throw in a replacement bearing and possibly holder/cap (I'm inclined to not trust the old one), and back to work.
Regarding torquing things down... heh. There's some stuff where you go Tight As Possible-- put a 3/4 drive bar on the nut or bolt, put 3 or 4 feet of pipe on the bar, and go til something stops moving. Then there's more delicate stuff, where I use an undersized ratchet (such as 1/4 drive instead of 3/8) and go until 'firm'. The two levels in the middle are 'go until it squeaks' and 'use the right sized wrench, go until tight but don't put extra effort into it'.
Ya, a tap to cut a thread. That was the term I was looking for when writing a request to fix a plumbing problem at work. There's a water outlet I need on the outside of the barn. I've set up a hose that goes from there to the freshly dug and clay filled hog wallow. Problem is, the cut-off valve inside the barn has a bleeder valve (to make sure the short section of pipe to the outside is water-free when it gets shut for the winter) and the bleeder valve has a brass cap that screws on. That cap has vanished, as small things are wont to do. There are none in stock, so either I borrow a cap from another valve when I want to water the hog wallow, get the entire valve replaced, or, have a new thread cut _inside_ the bleeder pore and use a standard brass (or non-reactive metal) screw to plug the hole. A kind of screw that's always in stock, so, lose the screw? Don't care, go get another one. Quick fix.
¡Wow! This all seems needlessly complicated. It would should be nice if everything would be standardized, but that would allow people to keep their cars running on generic parts for decades and millions of miles.
This forces people to buy a new 1 because they cannot get parts for the old 1.*
* If only would be low on money but long on time, one could skip the thousands of dollars in labor from workers in the factory by building a car from scratch out of generic parts (not a KitCar, but a car made from random generic parts from random different manufacturers). ¡That ain't gonna happen!
I thought it was "Tighten until you hear the *crack* (or starts to loosen, whichever comes first) then back off a quarter turn"
