Pete

Hello,

I have a 2002 C230K Coupe (2.3L engine, M111 engine). I have a P303 (cylinder 3 misfire) code.

It originally happened about 4 months ago, when I turned the car on from a cold start, and it was very rough. So, I turned it off and back on, and the problem disappeared, but the CEL remained on. So, figured that it would go away, because the problem appeared to go away, even after quite a bit of driving and on/off cycles (several weeks). Well, the CEL didn't go away. So, I disconnected the battery, waited 10 minutes, reconnected the battery, and I still received the CEL. So, I had the code read and it was a P303 (cylinder 3 misfire). Since the car has almost 95,000 miles, I figured that I would change the spark plugs, as I would need to soon anyway. I did that, and it still hasn't fixed the problem. So, I am planning to replace the coil-pack for that cylinder. Which is cylinder 3? Does it go 1-2-3-4, from the front of the car to the firewall?

Any other suggestions? The car seems to be running fine. Unfortunately, I need to get the emissions checked soon, so I do need to resolve the problem.

Thanks for any input.

-Pete

Glyn M Ruck

Replace all the on plug coil packs. You are in the trouble zone on a M111. Also check plug wires. That might be all that's wrong.

Pete

Glyn, thanks for the quick reply. Someone suggested swapping coil-pack #3 with a different cylinder, to see if the fault moves cylinders (which would certainly point to the coil-pack as the issue), so I think that I may try that first to see if that's the problem. How can I check the plug wires? Also, are those easy to replace? I wouldn't imagine that they would be easy, based on what I saw, when I replaced the plugs...

Thanks again.

Glyn M Ruck

Yes. Thats the good old favourite. You will find many of us suggesting that on many threads.

Swap the plug lead between cylinders as well. Measuring lead resistance is the other way but at your mileage & seeing it's only 4 leads & not 12 like a M112 V6 I think I would toss the plug leads as well. At 100K leads & coils are suspect.

Pete

I swapped coil-pack #3 and #2. The misfire is still in cylinder #3. So, it's not the coil-pack.

So, it's okay to swap the wires between cylinders? That won't cause a problem? Actually, I'm not even sure that they'll reach. Are those wires easy to replace?

Glyn M Ruck

As long as you have compression on that cylinder i.e. no burnt valve then the reasons for a misfire are either spark or fuel. You can compression test to check.

Check the wire, swap if it will reach otherwise replace. They are easy to replace.

Listen with a screwdriver to your ear & make sure the injector is clicking.

Pete

Thanks, Glyn. I did swap wires between 2 cylinders (#3 and #4). It seemed to run very rough, with the wires switched. I don't have the OBD2 reader, so I've been going to the local auto parts store for a (free) reading. I didn't want to drive it over there, with it running rough like that. So, I swapped the wires back, and I'm still not sure if the wiring is the issue.

Hmm, I wonder if I should have the compression checked, to rule out an issue with the cylinder.

> Listen with a screwdriver to your ear & make sure the injector is clicking.

How do I do that?

Glyn M Ruck

When I say swap wires I mean the whole wire. Not just plug end.

Use a screwdriver to your ear as a stethoscope.

C230 Sport Coup

Glyn, there are no plug wires on an M111 at least not in 2002.
Gotcha!!! You have officially (for once) given out a small piece of bad advice. HE HE HE EHE!!!

As to the source of the problem, hmmm.
New plugs, swapped the coil pack.

Since I never had a coil pack last more than 50K miles,
I'd still try a new one for sheets and giggles, and then a compression check,
and possibly put some Techron in the tank to clean the injectors.

Glyn M Ruck

No problem Todd - You know the M111 better than I do. So it's harness direct to on-plug coil. So by definition no HT plug wires but still plug wires nevertheless.

What are the chances of harness trouble with cam sensor leak etc? Or just wire trouble?? Benz had engine harness trouble on early iterations of the M111

You help Pete - I hope he does not have a buggered injector.

Glyn M Ruck

Pete - listen to Todd - He knows the M111 backwards.

Techron in the tank - try and ensure injector is ticking
Compression test engine
Replace one coil

Make sure that the Cam sensor on the front of the engine is not leaking oil into the harness. common problem if you don't have the pigtale fitted

I'm sorry - I was wrong for the M111 - Checking the harness wire for that cylinder is very difficult. You need to make sure it is giving the coil a LT pulse. I guess you could use a meter. I'm so used to working on engines with coilpacks & not on-plug coils that I suffered brain fade.

Pete

Glyn and Todd,

Thanks for the clarifications. At first I thought that Glyn meant to swap the wire harness plug from one cylinder to another. Then I thought he meant to swap the entire wire and harness plug from one to the next, which did not appear to be easily doable.

OK, now about the injectors. Will a bad injector give the same code (P303, cylinder 3 misfire)? I thought that the fuel system and injectors gave different codes. In any case, I will definitely try the Techron. Stupid question: where are the injectors and where should I place the screwdriver to ascertain whether it's clicking or not?

I'm certainly not adverse to changing the coil (or all of them, as it seems like it's time to anyway), but since it does not appear to be causing this particular issue, I'm hesitant to spend more money than is necessary, at this point. If there really is a cylinder compression problem, that may be too expensive to repair, and the money that I've spent on this issue will be for nothing. If I can resolve this issue, I'll be glad to do some other preventative maintenance (coils, etc.). So far, I've only bought the spark plugs and fuel filter. The car is almost 9.5 years old, so if there is a serious engine problem, I may have to get rid of it. The worst of it is that it seems to be running fine, but I need to get rid of the CEL to pass the emissions test, by the end of the year.

So, I think that I'd like to get the compression tested first, to rule out a major engine problem. As for getting the compression checked, should I try this myself (using one of the manual gauges that replace the spark plug), or should I just take it to a mechanic? From what I read, it can also be measured electronically, without taking out the plugs, which would require a mechanic with such equipment. Any thoughts?

I was actually going to look into the CAM sensor issue, as it appears that it's common on these engines. Would that potentially cause the issue that I'm seeing?

Thanks again for your help. It's very appreciated.

Glyn M Ruck

Oil in the wiring harness can give you what you are seeing. Pull the plug out of the single cam sensor on the front of your engine & look for oil.

See here

https://mbworld.org/forums/c-class-w...placement.html

Get the compression test behind you. Pull the plugs & just get someone to crank the car & use a manual compression gauge in the plug holes. You can pull the ignition fuse for safety if you are worried about spark. I never bother. Remember to have throttle wide open when you test.

44 are the injectors (Motronic)





Good luck

Pete

Thanks for the info, Glyn. I will check that, also.

I do have an update...

So, I was thinking about the fact that the car seems to be working fine, and that the car only started up rough once (when the code first appeared), months ago. I wondered if maybe the code was old and that the problem was actually gone even though the CEL persisted. So, I went to the auto store, to pick up some Techron and to ask them to reset the code, to see if it reappeared. (The previous times, the code was just read, not reset.) So, he said that he would reset, even though he wasn't supposed to. Well, they read the codes and there were two: a P303 and now a P304 (presumably from when I swapped the wire harness plugs from #3 and #4, and it started very roughly). Then they reset the codes. I started the car and drove for a few miles, and so far, no codes.

So, I think that the code may have been very old, but I have driven the car a lot since it first appeared. Shouldn't it have gone away, after a certain number of starts or miles? Also, I pulled the battery, several times, which I was told should reset it, but it never went away. So, I believed that there was a real problem.

Or maybe the new spark plugs (installed Saturday) fixed the issue, and I haven't driven enough miles yet to clear the code. But I did pull the battery, after installing them.

Any thoughts on the codes, and what can reset them (other than having it done, though the code reader)?

I'm also tempted to get the emissions tested ASAP, but I recall hearing that a certain number of miles need to be driven after a reset for the test to be successful.

So far, though, I'm pretty optimistic.

Glyn M Ruck

The vehicle will store the codes until it runs out of storage space if not cancelled. The CEL should reset after XYZ starts but sometimes does not.

I'm also optimistic - I'm suspicious that you might still have a borderline coil. Try it for a few days. If no more CEL then be happy. If it comes back or the car runs rough then compression test to get that behind us. If it had a burnt valve there would be a popping at the exhaust.

The M111 is not the smoothest engine Benz have made but it is as tough as nails. Blows the odd head gasket - more a leak than a blow - or has the odd electronics glitch but it is mechanically tough.

C230 Sport Coup

Yup.
I got the leak on the rear right side by the exhaust, but
my local indy guy, said just keep driving it.
It's a VERY stout engine.
Don't hear of many major problems.
Like Glyn said, make sure you don't have oil in the harness,
see the many articles on cam sensor leak.

Well, get the compression tested just to be sure.
If it all looks good, I would invest in all new coils.
They are about 35 each if you order online.
Try rockauto.com or rmeuropean.com
Put some dialectric grease on the point of contact, that may help.

Old plugs stress the coils. Something I learned recently.

You shouldn't need to mess with the injectors.

I've had zero problems with injector, but I seem to go through
coil packs like crazy. Damn things get cooked sitting on top of the head.

Invest in a code reader, only about 50 bucks or 100 for the carsoft
knock off from alpha-bid.com

Slyder

Great info guys. Thanks, i had many of the same questions. Just got the recall cam sensor issue resolved. But i too have had these symptoms. Also, thnx for the code reader link !!.

What Plug/wire brand would you advise. Best performance wise...
SlyDrJ