A Day in the Life of AMGtech: Crazy Diagnosis Edition

"AMGtech - now with more recalls!" (amgtech) 10/14/2016 at 15:17 • Filed to: None

52

27

Admittedly, the diagnosis part of my job usually doesn’t take more than an hour for any given car or problem. But every once in a while a car comes in with a problem that defies logic and baffles everyone in the shop. This is the story of one of those cars.

The customer purchased a non-running C32 AMG for about 30% of what they sell for in good running condition. Previous owner had already tried getting it to run but was obviously unsuccessful. Previous visit to a dealership was three months prior with complaint of an “engine noise” and the mileage was basically the same since.

For those who don’t know or don’t care to look it up, the C32 has an 18 valve, SOHC, supercharged V6 with two spark plugs per cylinder.

Engine cranks over beautifully, sounds totally normal, except for when it occasionally seems to backfire slightly, which tended to happen after sitting for a few hours but not after 10-15 seconds of cranking. But it just won’t fire and run. Now is the part where you go through and check all the basics; spark, fuel pressure and volume, injector pulse. Did that, all tested fine, even checked spark and injector pulse on every cylinder instead of just one like people usually do. Checked all the fluids for level and condition, fine. Checked the oil cap for the foamy white stuff you get from bad had gaskets and such, totally clean. Hmm, that’s weird, why won’t it start?

Next step is to check compression, so I pulled one plug from every cylinder and found them all to look normal but we’re soaking wet with a strong fuel odor. Makes sense considering it won’t run. Checked compression and found it to be 9-9.5 bar, totally fine for a stone cold engine with fuel washed cylinders. While the plugs were out I decided to have a look at the cylinders with the ol’ trusty colonoscopy cam, or bore-scope as it’s more commonly referred. Found the cylinders to be damp but no signs of damage and no standing fluid in the pistons.

Ok, clean and dry all the spark plugs, disconnect the injectors and crank the engine over a few times to dry out the cylinders just in case it is too wet to fire. Slapped it back together quick and cranked it over. And BAM! It fired and ran for all of 3-4 seconds before stalling! Must have been too wet, but why won’t it stay running and how did it get so wet?

Next I tried running it on an external fuel source introduced straight to the fuel rail to rule out fuel quality, pressure and volume even further, no change. Then I used a very fancy tool (read: screwdriver stuck in the plug wires and held varying distances from metal surfaces) to check the strength of the spark/coils, and found the spark to be very strong and easily jump 1" gaps.

Hmm, maybe we’ve got poor spray patterns from the injectors, but all at once would be really weird. Another possibility is incorrect cam timing. So I pull the right valve cover off, set the crank where it needs to be and try to install the locating jig on the cam, no go, it won’t fit because timing is off! I’ve seen stretched chains on these engines before but never cause a no start and they’re really rare. So then I turned the crank until the locating jig would drop into place, then checked how fast the crank had rotated, 100°! The chain appears to have stretched 100°! That’s insane! So I used to colon cam to look inside the timing case cover for damaged sprockets and chain guides, but everything looked perfect. Rotated the engine over slowly by hand a few times to listen for abnormal noises, but heard nothing.

So then I rolled a new chain into it. For those who don’t know, on most Mercedes, you separate the old chain then use a temporary link to connect it to the new chain, just rotate the engine until the new chain is in and the old chain is out, then install the permanent master link on the new chain. Easy peasy. After installing the new chain I measured it all out and found timing only improved by about 15°. Well maybe the chain jumped, so I completely correct timing on both banks so I had to pull the other valve cover off as well. After doing that the engine would only rotate about 90° in either direction. Very strange.

Wait a second... What if the timing marks on the crank pulley are wrong? So I pull the #1 plug and manually find TDC. Low and behold, it’s exactly the same distance off the marks as the cam timing. Crap, the pulley rotated on itself, which is so incredibly rare on Mercedes that most (all but one actually) techs I talked to about this never even knew this was a possibility. You see, the pulley consists of the parts: the inner which mounts to the crank, a rubber damping section, then the outer pulley section. Turns out the rubber section became unbonded enough to allow the outer to rotate independently of the inner. The timing marks are on the outer.

Okay, replace the crank pulley and set timing up all over again, reassemble the engine completely and go to fire it up. POP POP POP! Backfiring some more and then completely back to how it was originally. Go back through every diagnostic step all over again to make sure I haven’t missed something. But this time while the plugs were out I measured piston height on every cylinder to rule out bent connecting rods, all equal down to the millimeter. Fine, be that way.

Let’s smoke the intake for leaks, just for fun. Found a few little leaks and fixed them, but nothing bad enough to cause a no start. So now I’m thinking, stretching really, that maybe this car had a whole bunch of little problems all adding up to a no start...

At this point, as I’m sure you can imagine, I’m frustrated and starting to feel defeated, but I’m also intrigued and not about to give up.

On to the only other thing I can think of, the injectors. So I remove the throttle body and charge/boost air manifolds to get to the fuel rail. As soon as I get those off I find they’re disgustingly coated in that milk-shake-looking-crap that you get when oil and coolant mix. That’s really strange, especially since all the fluids are perfect and the air boxes/intake prior to the supercharger are all clean. Anyways, with the charge manifolds off I can clearly see the injectors so I have another guy crank the engine while I watch.

BANG! Engine backfired, my face melted off, and I died.

Ok maybe not, but if you do this, protect yourself, I had full face protection and more helpers nearby just in case, this IS dangerous.

Ok back to the story. Injectors all sprayed perfectly and evenly. So let’s see if we can get to the bottom of this milk shake thing going on in here. Have a look down into the water-air charge air cooler situated below the supercharger and find that it is half full of coolant!

So when the engine cranks it pulls just enough coolant into the cylinders to extinguish the spark, which is why it would try to fire after sitting and ran briefly after drying the cylinders out. Couldn’t smell coolant on the plugs because fuel smells so much stronger. So the charge air cooler is leaking coolant internally, causing the no start condition. Looks like the veritable smoking gun to me. It’s about damn time.

Jcarr > AMGtech - now with more recalls! 10/14/2016 at 15:23

1

This was interesting Kinja.

macanamera > AMGtech - now with more recalls! 10/14/2016 at 15:25

1

Holy shit this was interesting.

ShrimpHappens, née WJalopy > AMGtech - now with more recalls! 10/14/2016 at 15:27

4

10/10 would read again

Daily Drives a Dragon - One Last Lap > AMGtech - now with more recalls! 10/14/2016 at 15:31

1

Wow that’s quite the adventure to get a car to start.

V12 Jake- Hittin' Switches > AMGtech - now with more recalls! 10/14/2016 at 15:35

1

That’s crazy

Future next gen S2000 owner > AMGtech - now with more recalls! 10/14/2016 at 15:36

6

This is why some mechanics are better than others.

Boosted2k - I Make Videos and Put Them on YouTube > AMGtech - now with more recalls! 10/14/2016 at 15:41

1

Nice diagnosis! Glad you didn’t give up!

AMGtech - now with more recalls! > Boosted2k - I Make Videos and Put Them on YouTube 10/14/2016 at 15:52

0

Thanks!

RallyWrench > AMGtech - now with more recalls! 10/14/2016 at 15:54

1

Wow. Quite a journey you took there, but dogged determination is part of being a good diagnostic tech. What an unusual series of issues, I’ve seen a couple of M112s slip their pulleys, but never a chain issue. You earned a beverage at the end of the day, man!

Noah - Now with more boost. > AMGtech - now with more recalls! 10/14/2016 at 15:59

2

This is the most interesting thing I’ve read on oppo in a while. Thanks! I feel like I learned a few things. Also, what an epic views vs. stars ratio - 102 and 25! Somebody FP this

AMGtech - now with more recalls! > RallyWrench 10/14/2016 at 15:59

1

Thanks! Those slipped pulleys were usually part of that recall though, and never came in not running. This car is a few years past the recall, and I don’t live in a hot climate so wet just don’t see it happen up here.

Manwich - now Keto-Friendly > AMGtech - now with more recalls! 10/14/2016 at 16:01

1

10/10... excellent Kinja.

Chasaboo > AMGtech - now with more recalls! 10/14/2016 at 16:05

1

Pure Genius!

JGrabowMSt > AMGtech - now with more recalls! 10/14/2016 at 16:11

0

Ive seen a freshly built motor be 180° out of timing and a complete no start, so I started to suspect timing from the beginning.

Would not have guessed the water to air though. Could the previous dealer have reassembled out of timing? Thats what I would guess if a new chain didnt completely remedy the timing immediately.

One heck of a car, and deal for that guy. Even with all the work, he can still profit on it quickly if he wanted.

AMGtech - now with more recalls! > Noah - Now with more boost. 10/14/2016 at 16:16

1

I’m glad you liked it!

AMGtech - now with more recalls! > JGrabowMSt 10/14/2016 at 16:21

0

It’s possible, but I have no idea what they actually did if anything. Unfortunately I can only read very small snippets of work done at other dealers.

Actually, considering the condition of the rest of the car, and the cost of all this, he’s way over what it’s worth. It’s a salvage car that was poorly repaired and still needs lots of other work besides, but it wasn’t relevant to the story so I left that bit out. He could have put that money into one in good condition and had some left over. But had the gamble paid off, yeah, he could have come out way ahead.

gmctavish needs more space > AMGtech - now with more recalls! 10/14/2016 at 16:25

3

This reminded me that I want a C32, which really shouldn’t have been what I got out of it

Rust and Dust - Oppositelock Forever > AMGtech - now with more recalls! 10/14/2016 at 16:26

0

Thats one of the jobs you end up walking away from a couple times to reset/refresh. Nice writeup, never would’ve guessed an intercooler turned fire supression system.

JGrabowMSt > AMGtech - now with more recalls! 10/14/2016 at 16:32

0

Ah, salvage no bueno.

Well, I hope he drives it until the wheels fall off because it owes him now.

AMGtech - now with more recalls! > Rust and Dust - Oppositelock Forever 10/14/2016 at 16:50

0

Definitely. Actually had to go to training for a few days right in the middle of it, and some of the parts were special order.

AMGtech - now with more recalls! > gmctavish needs more space 10/14/2016 at 16:51

0

If you really want a C32 then you should really have a C55. Better in every way imaginable.

DipodomysDeserti > AMGtech - now with more recalls! 10/14/2016 at 17:22

1

I was wondering at which point you would have assumed there was an Elf living in the engine and just poured some Weihenstephaner in there to appease him.

gmctavish needs more space > AMGtech - now with more recalls! 10/14/2016 at 18:19

0

That’s a very good point. E55s also intrigue me like no other W210

AMGtech - now with more recalls! > gmctavish needs more space 10/14/2016 at 18:21

2

That’s why I own one 

they-will-know-my-velocity > AMGtech - now with more recalls! 10/14/2016 at 18:48

3

This just reinforces my immense respect for AMG techs and validates my decision to never buy a Mercedes to work on myself newer than 1985.

AMGtech - now with more recalls! > they-will-know-my-velocity 10/14/2016 at 20:42

0

Be careful there, the old stuff is complicated and even more weird.

sdwarf36 > AMGtech - now with more recalls! 10/14/2016 at 21:14

1

I had Honda I was working on years ago while at an auto machine shop. Coolant in a cylinder. Ok-old enough to need a head gasket. We surface the head + give it back to the mechanic. He comes back a few days later-he’s still getting coolant in the same cylinder-wants the head pressure tested-it passes fine. We re surface the head with a brand new cutter just to be sure-tell him to check the block for flatness. He calls back in a couple days with the same happening. The boss says pull the head-and bring everything that attaches to it. We bolt everything together + pressurize the whole assembly. Water squirts out! Ah-ha! Now we’re getting somewheres. It turns out there was a pinhole in the intake manifold between water + a port that squirted water right into that cylinder’s intake tract. NOT what you expect from Honda-and not something you think would not show up until 80k miles.