Cylinder Misfires - PeachParts Mercedes-Benz Forum

mathesius · #1 12-22-2005, 08:30 PM

This is a long post, but I hope the extra detail might lead to better help. I posted part of this story earlier but got no replies. It's gotten more interesting since then.

I have a 1998 C230 and on my way to work about a week ago the CEL came on. I didn't notice any problem at highway speed but when I came to a stoplight a rough idle was obvious. The car has 91k miles on it. I bought it 6 months ago with 79k miles.

On the trip home (41 highway miles) there was an obvious loss of power so the situation was getting worse. I stopped by Autozone and got the codes read. They said cylinders 1 & 2 were misfiring and the EGR valve was also indicated. The exact codes are P0301, P0302, P0300, P0400.

I took a look at the wires and pulled one of the plugs which are all brand new just last month. I used OEM plugs, OEM spark plug connectors, and Magnecor wires. I had a heck of a time getting the connector out on #4 and must have damaged the spark plug seal. Now there was some oil in the area by #4.

I took it in to the dealership, because I couldn't find an easy way to take off the EGR valve to check it.

It turns out my EGR code was a stored code, not an active code. Since I didn't know when the codes were cleared last, I have no idea what set that or when.

Cylinder 2 misfire was the only active code per the Zimbrick dealership.

They found the center electrode on the plug in cylinder 2 had disintegrated (a bit of it was in the top of the cylinder, which they got out somehow). They also didn't like the oil near cylinder 4 and wanted to replace that plug too and change the valve cover gasket set. They actually ended up putting new plugs in cylinders 1 & 2. Discarding my old plugs from cylinders 2 & 4, and putting my two remaining plugs in 3 & 4. If you can follow that.

Thus at the end I had two dealership installed plugs in 1 & 2; two of my plugs in 3 & 4, and a new valve cover gasket set.

Clean running... for a week. Then today I accelerated strongly to pass a car and the CEL came back on and the engine ran rough again. Same as before, it started with a rough idle but progressed to a loss of power at highway speed.

I took it back to Zimbrick rather than deal with this. Turns out cylinder 3 & 4 were misfiring, so they changed out the plugs in 3 & 4 -- so now all four of the new plugs I put in 6 weeks ago are replaced with new plugs they put in.

Drove smooth home. Until I accelerated strongly to test things out.

Bingo, the CEL came on, the engine got rough even faster than before. I made it home, cleared the codes by unplugging the battery, and started it up.

No CEL, ran smooth at idle. Ran smooth at 2000 RPMs. At 4000 RPMs it went bad again, causing misfires and rough running at any speed just as before.

Short story:

Something is triggering at higher RPMs that causes the whole engine to misbehave.

Possibly this is causing it to misbehave so badly that it's ruining plugs.

Any guesses?

I am running a K&N air filter, but the MAS hasn't yet sent a code and from what I can tell most bad Mass Air Flow Sensors throw codes. The dealership did warn me against the K&N though. I've had the K&N in for 12,000 miles.

I am going to do more research online and probably take it back to the dealership tomorrow.

Thanks for any help!

#2 12-22-2005, 08:38 PM

first off trash the K&N, you are asking for a future costly repair, why don't you clear the codes and switch the coils, besure to mark the ones that were originally misfiring and see if the misfire move with the coil, how is the engine wiring harness? after switching the coils try to get the codes pulled by a dealer or someone with a factory mercedes tool, if it is still doing the misfiring i would replace the crank sensor, but before you do disconnect it and see if there may be water or other liquid on the terminals. i have seen a few crank sensors cause this issue. if you do replace the crank sensor it is a good idea to reset the sensor gear adaptation, i believe the mercedes tool is the only way that is done

Arthur Dalton · #3 12-22-2005, 10:53 PM

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Are you talking misfires at 4K rpm in P/N ????

mathesius · #4 12-23-2005, 07:27 AM

The codes have not yet corresponded to a coil. The misfires a week ago was 1 & 2, the misfires yesterday were 3 & 4. On my engine coil 2 fires plugs 2 & 3; coil 4 fires plugs 4 & 1. I was hoping I'd find a pattern suggesting coils, but nothing yet. Thanks for the tips!

mathesius · #5 12-23-2005, 09:08 AM

Also, it is very predictable. The 4k RPMs I cited was in drive.

- clear the computer codes (disconnect / reconnect battery)
- drives fine on short trips & medium trips if RPMs < 4,000.
- accelerate into high RPM range (4-5k RPMs), CEL comes on, loss of power at high RPMs, engine rough at low RPMs. The engine problems happen immediately when the CEL comes on, as if a switch was flipped.
- repeat

Is this the limp home mode kicking in?

E.g., the computer detects a misfire at high RPMs and deactivates a couple cylinders. On a 4 cylinder car, losing 2 cylinders causes the loss of power and rough idle. When the codes are reset the limp home mode is cleared & it runs fine until the code gets set again.

It's frustrating in that the only codes getting set so far have been misfire codes.

Arthur Dalton · #6 12-23-2005, 09:16 AM

The car has a 4K rev limiter for P/N to protect the torque converter from operating at high RPM w/no load. It works by dropping a couple of cylinders. It is over-ridden by a speed senor when the car is moving.
Next time it starts to misfire on the road, put it in N and see if it clears up.
Should go up on tach easily.
That will help narrow down the diagnosis and indicate that part of the system needs to be checked.

Smokiesman · #7 12-23-2005, 10:46 AM

Not sure on your car, Does it have a dist cap and rotor? I had sort of a prob like this on my E420 and found that I had bad caps and rotors. Was told by a very good source that if the computer detects a misfire it will cut out the ign on on half the cyls to protect the cats. I replaced both caps and rotors and put in a new set of plugs and BigBlue has been purring like a kitten!!

Smokie

Arthur Dalton · #8 12-23-2005, 10:49 AM

Car is DIS ignition..................

#9 12-23-2005, 01:34 PM

Quote:

Originally Posted by mathesius

Also, it is very predictable. The 4k RPMs I cited was in drive.

- clear the computer codes (disconnect / reconnect battery)
- drives fine on short trips & medium trips if RPMs < 4,000.
- accelerate into high RPM range (4-5k RPMs), CEL comes on, loss of power at high RPMs, engine rough at low RPMs. The engine problems happen immediately when the CEL comes on, as if a switch was flipped.
- repeat

Is this the limp home mode kicking in?

E.g., the computer detects a misfire at high RPMs and deactivates a couple cylinders. On a 4 cylinder car, losing 2 cylinders causes the loss of power and rough idle. When the codes are reset the limp home mode is cleared & it runs fine until the code gets set again.

It's frustrating in that the only codes getting set so far have been misfire codes.

did you read what i posted in post 2 above?

mathesius · #10 12-23-2005, 03:54 PM

I did read post 2. The misfires have occurred in all four cylinders, not following an ignition coil.

I took it to the dealership today hoping they could find the problem & fix it fast.

The dealership swapped my ignition coils around and the problem today stayed in cylinder 4, also not following a coil. They also tried a new mass air sensor but that didn't fix it, so they reinstalled my original one. They detected a rattling sound in part of the pipe that goes to the muffler, disconnected it, but that made no difference. They buttoned everything back up, no cause found. I'll be able to work on it at home over the holidays.

I see no reason why both of my coils didn't age at the same rate. Thus, if a coil is bad, perhaps they are both bad.

I'm tempted to buy two new coils online for $100 and just replace them.

I'm probably not competent enough to handle the crank sensor work you describe.

Thanks for the help

Arthur Dalton · #11 12-23-2005, 05:32 PM

These are by far the most common misfire code culprits.
...and as they are only $8 ea , most techs just change them for easy diagnosis..
I would get two and try them before doing anything else.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1M30LAGSC1OW11DN02&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1998&product=F1010-84561&application=000429429

#12 12-23-2005, 05:36 PM

Quote:

Originally Posted by mathesius

I did read post 2. The misfires have occurred in all four cylinders, not following an ignition coil.

I took it to the dealership today hoping they could find the problem & fix it fast.

The dealership swapped my ignition coils around and the problem today stayed in cylinder 4, also not following a coil. They also tried a new mass air sensor but that didn't fix it, so they reinstalled my original one. They detected a rattling sound in part of the pipe that goes to the muffler, disconnected it, but that made no difference. They buttoned everything back up, no cause found. I'll be able to work on it at home over the holidays.

I see no reason why both of my coils didn't age at the same rate. Thus, if a coil is bad, perhaps they are both bad.

I'm tempted to buy two new coils online for $100 and just replace them.

I'm probably not competent enough to handle the crank sensor work you describe.

Thanks for the help

if the misfire did not follow the coil then the problen is likely the crank sensor. i have seen it before, did you look at the plug to see if it was wet? i have seen moisture espescially coolant from a previous leak accumulate there and cause misfire, pull the plug on the crank sensor and see if it is wet.

mathesius · #13 01-02-2006, 09:57 AM

As a conclusion, it ended up the catalytic converters were partially blocked. The dealership figured it out after measuring the exhaust gas temperature before the catalytic converter and it was too hot, indicating back pressure.

At low RPMs the exhaust system was clear enough to run fine. At higher RPMs the extra demand put on the exhaust resulted in back pressure which caused the cylinder misfires. The computer then shut off the cylinders until I reset the codes.

I went ahead and replaced the muffler pipe too since it had a slight rattle in it. Got the parts mail order to save some $. The catalytic converters new from Mercedes was going to be $1,500.

It was probably a combination of things that led to the catalytic converts failing. The car is 7 years old with 92k miles; it had a rough history before I purchased it (all four springs were busted when I bought it 6 months ago); recently spark plug 2 failed and while it was failing the exhaust would have been rich.

The O2 sensors aren't throwing codes, but I'm thinking about replacing them too just to be safe. If the front sensor is bad but isn't throwing a code, it could have caused the air/fuel mixture to be too rich, causing the old catalytic converters to go bad. I'd hate to have my new cats go bad in six months due to the O2 sensor. I've read O2 sensors usually should be changed around 100k miles anyway.

Thanks for all the help.

Cheers, Steve

C230 Sport Coup · #14 09-25-2007, 01:00 PM

Ha, an old thread, but the 1st thing I thought was the Cat as I've been down this road.

zcc · #15 09-25-2007, 01:27 PM

This is not an answer. But personally I hate the C class. It always misfire.