Lenin

A few days ago on the way to work I got into a race with another Benz. After 1/2 mile and being well ahead, I look down and see a Check Engine light is on.
Before I go on, a little bit about my car. Its a 2002 C32 with 100K mile on it. I'm running LET 181mm pulley and a LET tune, CM30 pump, Supersprint exhaust without secondary cats and no resonator. Supersprint exhaust without secondary cats is 2 weeks old. The rest I had for a year. Stock wires and plugs.
I'm also using a DashDaq OBD2 monitor and I know that in the process of running away from the other Benz I did get to 21 PSI boost. So, I check the codes. It's P0306 - misfire on cylinder 6. By this time I'm in limp mode. I clear the codes. Check them again, all while limping to work. Now I have P0300 and P0301 - P0306. So, I take the car to my mechanic, we hook it up the the STARS laptop and see that cylinder 6 is just not the same as the rest of them. By now we tested the gas and see that it has some water but not enough to cause this kind of problem. We replaced the #6 fuel injector without any positive effect. Looked inside with the bore scope and everything looks good and clean. Compression test, including the wet test, however is failing.
Will be opening it up on Monday. Stay tuned.

mkonei

consider doing a leak down test on all the cylinders? @ 21 psi with 100k, you might have broken a compression ring. that might be hard to see with a bore scope. good luck, hopefully its nothing major

Carl Lassiter

A faulty valve spring would the first place I'd look for cylinder misfire. I've dealt with this in the past and it's an easy fix so hopefully that turns out to be it. Good luck.

Lenin

Carl,
I'm also hoping that it is only a faulty valve spring and not ring. The worst would be if the cylinder walls were washed down with excess fuel. I don't know what my AFR was before the tune and after the tune. I just installed the Zeitronix Wideband sensor and EGT sensor but did not get a chance to hook it up to the controller. As you know, LET tune has issues with AFR above 5000 RPM and high boost. You also may have seen a thread on the X-fire forum about a blown M112K engine. So, lets hope it is just the valve spring.

Bulldogger

With stock intake plenums your still okay fuel wise, if you have modded the plenums or have needswings intake plenums, then you will be running lean up top depending on the temperature in your area.

splinter

Sorry to hear about your situation.

Best wishes for a simple and inexpensive resolution.

Lenin

I'm running a full SL55 intake, but stock TB and Y-pipe.

Bulldogger

With that set-up you should be okay fuel wise. If the bore scope looked okay no scratching on the cylinder walls, then the piston rings should be okay. Next would be head gasket or valves.

mkonei

possible detonation in #6 that popped the head gasket? that would explain the initial misfire code, and then the failing compression test. no bubbles in the cooling system, sweet white exhaust, or milkshake for oil? the pressure has to be going somewhere. i blew one a couple years back that actually went outside...i thought it was the header flange leaking!

Lenin

Update.

After opening up the engine, it looks like the exhaust valve on #6 hit the piston. At this point we are looking to replace the valve, rocker arm and the hydraulic lifter. Anything else?
The cause is still unknown. We considered that the engine was over revved somehow but my ECU is set to 5750RPM at 100% and 6600RPM at 67% while stock was at 5500RPM and 6300RPM. Not much different than stock. One other cause may be a separation of the hydraulic lifter. Not a common problem like the IC pump, but previously reported on a number of occasions. And there is always a possibility of spark plug getting old and causing a major misfire. To be continued.

splinter

Any luck with definitively ascertaining the cause of its failure during the post mortem?

Trust you’ve buttoned everything back together and it’s running well once again.

Lenin

Thanks for asking, but the car is not running yet. After further analysis it appears that the exhaust valve floated and came in contact with the piston. The valve and the piston need to be replaced. The feeling is that it happened because the engine overreved. How it can overrev given what Jerry told me about the limiter settings is a mystery. We don't have another theory.
As you may know, to replace the piston you need to take out the engine. I'm also replacing the mounts and the timing chain while I'm at it. The parts came in yesterday and hopefully by Wednesday we will fire it up again.

mkonei

a weak valve spring can cause valve float as well. if you plan on running the car hard, it might not be a bad idea to change them all out. most springs can be done with the heads on, i dont see why the MB would be any different.

splinter

Ouch. That’s a damn shame.

What were the actual peak revs you’ve recorded during data logging – if you don’t mind sharing? Have another sponsor’s conservative ECU tune with which I sheepishly selected the “no” option regarding raising its OE RPM limits. Just don’t have the billfold to be swapping pistons. Perhaps its #6 exhaust valve spring was toward the soft end of the strength tolerance as delivered from Affalterbach?

Good luck with getting everything back to full vigor.

Lenin

Unfortunately I was not logging when the problem occurred. I do have logs from previous runs and will take a look when I get back home (at the beach now). Hi RPMs is just a theory. Jerry/LET says that it base RPM limit was not raised that much. It may be just a bad spring. The car is 100,000 miles away from Affalterbach. Anything could have happened along the way. At least half of these miles were of the water-boarding variety.
BTW, which ECU tune are you using?

splinter

=)

Powerchip's. Mixture strength and spark timing have been revised several times since the initial installation.

Your perspective regarding its heretofore 100,000 mile reliability is entirely valid.

AMG-Driver

Hello,

I also got a P0306 yesterday. The Freeze Frame says P0300 and 19.4PSI. It happened at approx. 6.200 RPM. I have a Pulley-Ratio like the 185mm Crank Pulley. When I stopped at the road, the engine was shaking real bad.
After stopping the engine, and starting it again, the engine ran fine again. No shaking and it is running very strong again. l had no CEL. My spark plugs are 7.000 KM old and my car has 40.000 KM . Is it possible that the ECU shut down the Cylinder 6 for Security reasons because of the misfire?? No the car runs very strong as nothing has happened...

Lenin, was your engine also shaking because of Cylinder-Shutdown? Did you noticed power loss after this incident?

Thanks.
Kind Regards

Lenin

That's exactly how it felt. Shaking and major power loss. Like driving through mud. How did you get to 6200RPM? I think I remember you doing some work on your car in Germany. Did your tuner raise the rev limiter or removed it all together? How often do you approach 20PSI at above 5800RPM?
My car is back together and running. I'm picking it up in a 4 hours. (I'm counting hours. I can't believe it. A grown man. Need to see a shrink about this ). Will report later after some testing.

AMG-Driver

The Rev-Limiter was raised by my tuner. I reached around 20PSI often.Did your car ran fine after restarting or did it again run shaky? GOOD LUCK with your car!!

pullejo

Exact same thing happened to me back in Nov...while accelerating moderately...and at about 35 MPH.

We ended up assuming that a piece of carbon may have lodged open the exhaust valve...or...it could have been a bad spring...and the #4 piston came in contact with the valve bending it and preventing it from closing - thus dumping my compression. The car, when cold, would run ...but as soon as the valve warmed up and expanded, I lost compression on the cylinder.

You can see on the piston the scar from where it actually came in contact with the valve.

Gave me a chance to look at everything when it was all apart though - cylinder walls were fine.

Ended up replacing a lot more than I probably needed to.

Lenin

I have an update but it is not a story with a good ending (so far).
This past Saturday the shop completed the installation of a new piston #6, new timing chain, new exhaust valve and the rocker arm, crank position sensor and a few other things. I picked up the car and drove it for 35 mile while only twice reaching 3K RPM. Everything feels fine. Around 8:00pm I take my wife in this car to a party to celebrate her birthday. 10 mins into the trip, the CEL comes on and the car starts shaking. I'm dataloging the entire trip and I know that it crapped out at 3K RPM. I check the codes and it is again, P0300, P0304, P0305 and P0306.
I clear the codes, start the car, but they come back. Conveniently, I'm only a few blocks away from the restaurant and about 10 blocks away from the shop.
Come Monday, the heads are removed and my new piston#6 now looks like the one in Pullejo's picture and the valve is damaged again. After close examination it appears that a rocker arm from an E55 is installed in place of the C32 one. They look identical, but the part numbers are different (both start with 113). Can this be the problem this time? Who knows. We install the correct rocker arm leaving the scarred piston in place. This is not as bad as the original damaged piston and should be fine. Its already Tuesday afternoon. The car idles for an hour and appears to be fine. But I want my mechanic to road test the car for a day first. Well, on the way home, only after a few blocks, the P codes come back. Good thing that he was driving.
At this point he doesn't know what to think. Is the misfire a cause or an effect? He is going to double check timing and I want him to check the cats. Specifically the drive side cat. I remember Jerry from LET having misfires and it turned out to be cats. #6 is the last cylinder on the driver bank, it is the exhaust valve that breaks every time. It may all be related. I'm open to other ideas

pullejo

Yep. We did the rocker arm, valve, spring, piston, rings, threw in a new cam for safe measure as well...

We had a similar issue after humpty-dumpty was put back together again - first test drive had the same issue (bent valve again) due to the rocker being put in BACKWARDS. Uggh.

$7300.

Funny thing was, two days before this happened I was on the phone with Jerry from LET getting ready to order some goodies but then once it did, I couldn't justify doing it. Now, 6 months later...it's seems reasonable to do so. ;-)

Having spent roughly $10k on this car last year I've decided I'm keeping it for some time so I might as well make it how I want it. I do still love it after all.

And for those of you who moan about that...I've got a much more painful story about a 1995 RX-7 R2 I had ($23k in one year). To me, the Benz has been a bargain.

Lenin

Latest Update.
Checked the primary cats. They appear to be OK. Not perfect but good for now.
Our current suspect are the cams. The 2002 cams are a multi-peace part pressed together at the factory. It is possible that the tolerance after 100k is not what it used to be when the car was new. The cams are driven from the front and over time, because it is not a one-piece design, the end part of the cam may have loosened somewhat. The end of the cam is what is driving the valves for cylinder #6 (#6 being the last cylinder) Also, and that may be the smoking gun, the MB EPC lists the original cam part # as A1120505391 and A1120504201. There is also a note next to both part numbers "Replaced by: A1120505301 and A1120505301. OLD PART MUST NO LONGER BE INSTALLED". WTF. What's wrong with the old part numbers? I guess I'm finding out.
These are all just theories, but I feel like I have no choice but to replace the cams. So now I'm looking for Kleemann or Schrick cams. Kleemann appears to be out of stock and I'm still looking for a Schrick source. Trying to avoid the OEM cams. Wish me luck.

Lenin

The car is back in working order. Had it for about 3 days and put 100 miles on it. For now taking it easy for the first 500 miles.
After looking everywhere for aftermarket cams, I had to go with new OEM cams and all 18 rockerarms with lifters. Big thank you to Jerry Thornton from LET for looking into the source for Schrick cams. It turns out that the tooling to make the cams got so worn out it had to be disposed off. So, no more new Kleemann/Schrick cams for the M112K crowd. In general, can't say enough about Jerry. He offered advise, used parts, and elaborated on the various theories we had. Super guy. But most everyone knows that.
So, lets hope this is the end of the problems and I get another 50K miles out of this C32.

AMG-Driver

Schrick decided to take the Cams out of their programm, but I don't think its because their tooling is worn out... They can build you ANY cam you want, if there is enough interest / market and it is profitable for them.

Good luck with your car