Misfiring
 

Took the SL600 from MD to Niagara Falls for the weekend, on the return trip we suddenly got a "check engine" light and it started running rough. At idle it was obviously not firing on atleast 1 cylinder, but shutting the car off and restarting took care of it for a while. Wouldn't even have to shut it off and wait, just off and right back on was enough. When it would start missing again it was really down on power, but after the restart it was it's torquey self again.

Going out and reading the codes with a regular OBDII reader this morning it's showing P0300 (multi cyl misfire), P0309 (misfire Cyl 9), P0311 (misfire Cyl 11), P0312 (misfire Cyl 12). But they are all historic codes, the "check engine" went out on it's own after a couple short stops just before getting home.

I'm thinking it's the coil pack but why would a restart have it working fine again. Wasn't doing anything special when it happened, just on some NY backroads with alot of radar, so sticking pretty close to the posted limit, no rain, no bumps........ Any ideas???

Mkhurely,

Your multi-misfire code PO300 usually indicates a misfire has been stored in the PCM. In your class cylinders P0309/310/311/312. It appears they are intermitant as the MIL is off and as you noted more than likely the coil packs. Reference your repair manual and follow details to check for proper cylinders/plugs and coils as indicated if you plan to diy.

Has the plugs and/or coils been replaced bnefore?

not sure how many miles u have on your car, but dont overlook the ignition control module, after 40k miles mine fried, I was throwing misfire codes, had it serviced 2x before they discovered. Car runs awesome now.

Guess I should have put that info out. It's a 2004 with just over 75k miles now. Don't know whats been done previously, just got it at 72k miles, do have x-warranty. I've been reading about modules that feed the coilpack, not sure how they work though. Thanks for the replies, I'm gonna check some basics and probably turn it over to the dealer for warranty work.

Check this out!
 

Problem has a v12 bulletin also "ethanol fuel system contamination"

https://mbworld.org/forums/mercedes-...g-running.html

Do your fuel and fuel system first. Bad gas up and down the east coast. Remember a big refinery just came back online!

:smash:

Finally got it into the dealer as it started happening more frequently, they are saying it's the "Charge Cooler Pump" ??? It's getting to hot and causing the misfires. I'm a bit concerned as shutting it off and then back on resolves it for a good while. If it were heat related I would think it would just start happening again right away.

Do I understand this "Pump" correctly, it pumps coolant thru the intercoolers to cool the "charge" air from the turbos??

You are correct. Just had mine replaced in the S600.
I wasn't having a misfiring problem, but I was experiencing a lack of power here and there. When they go bad, it will allow the IAT's to get very high and computer pulls timing & boost resulting in reducing the power...

Yeah, the pump didn't resolve the issue, not saying it wasn't bad, but the misfires are still there. I've got new plugs on the way, gonna change them out and see how it does. Dealer wanted $1500 to change the plugs, I told em they were smokin Crack....

To be honest, I think it sounds like coil pack issues.
Why not change one or both of the packs before the monster job of 24 spark plugs??

There is a great DIY tutorial for plugs here....https://mbworld.org/forums/m275-v12-...placement.html

Well, the plugs are ~$300, the coil packs are ~$1K each (rebuilt) and the X-Warranty company won't change the packs until the plugs have been changed. Codes don't show a bad coil pack, otherwise they would.

Yeah, I've had a good look at that and the other about replacing the coil packs, both are very helpful and let me know I can probably handle this without concern (well except breaking a coil pack). Plugs should be here tomorrow, might get started some evening this week, take my time, no rush, do it right.

Well started on the plugs today, UPS shows they are "out for delivery" so I hope they come in this evening. I pulled all the old ones, none showed any obvious wear, they all looked pretty good. They were at the very least OEM MB plugs, symbol and all, original or not I can't say. Took about an hour and a half to get em all out, not bad, another hour and half to two hours back in and together I'm figuring. All the silicone sleeves seem to be in good shape, none cracked or stiff. Coil packs came right out, no problem.

I gotta say, this car is pretty easy to work on, they put some thought into things, like leaving enough slack on the wires so you can get them around the coil packs. Every bolt I've touched has broken loose easy and after a couple turns could be taken out by hand, instead of the old broken off or fighting all the way to the last thread I'm use to in my domestic vehicles.

Glad everything is going along smoothly. I know I just got my Cl65 back from having both plugs and coils replaced. I was having the same problem rough idle, misfire if I went past half throttle or rolled on the throttle to fast. Now that they are changed it has its power back and I dont have to worry about the car misfiring and going into limp mode. It was all underwarrenty and the total came out to be $3461. I had a hard time tracking down the coil packs for the shop that did mine. Their parts department just put them on order from the local dealership and was just going to wait for them to magicaly show up since they are on backorder even in Germany. Good luck and I hope that you have the same result with yours. I know I was missing its power bad when I didnt have it.

Thanks, got it pretty much all back together now, snapped off the connector for one of the hoses going into the pressurized overflow for the radiator, no real way to block it off so I can't fire it up until I pick one up tomorrow, hopefully it's in stock.

Well got to drive it for a short time tonight, it seems smoother, of course that could be cause I haven't been in it for a week. Hasn't missed yet, but I'll need some more time to tell for sure if this took care of it or if it's going back for coil packs or controller. Sure missed driving it over the past week, not sure how I'm gonna handle parkin it for the winter. :eek:

good to hear its running smoother. the way i tested mine was to get it up to operating temp and just floor it. thats when i would have the problem. then i did a 0-100 run and it didnt misfire or anything. Hopefully it is fixed. i know how you feel about putting it up for the winter i know anytime we have a nice day this winter it will be out. but i do have my turbocharged truck to drive around if i cant take out the car.

I wish mine had a consistent reason, but it just didn't. Gotta put some miles on it and see how it does, hopefully this afternoon.

We plan on puttin our house on the market in the spring followed by a move to FL, so hopefully this will be the last winter I'll have to deal with.

i have a cl65 AMG with the same problem that you have... random miss-fire.. after replacing both coil rails, coil driver, spark plugs, airfilter and fuel filter, also re-timed the flex plate on the crankshaft... in the end (4-$5,000) later the mis fire was fixed.. and the answer was a clogged cat converter, lucky i was under the federal 8year 80k miles warrentee so i got it replace for free at the dealer...

Got an private message about this so figured I'd update here in case someone else has the problem. I took it to an Indy and he was able to diagnose it as the drivers side coilpack, replaced it about 1000 miles ago and it's been running great ever since. Hope that is the end of it.....

I got the old coilpack from him and opened it up, the tubes going down to the plugs, if they are twisted at all (can easily happen) they will short out or get close enough to allow the voltage to flash over, this could be causing it, not sure. The cylinders I was having an issue with, the tubes were twisted slightly, I'm wondering if the $1200 coilpack was replaced for twisted tubes. Never know though cause you pretty much have to destroy the cover to get it off the coilpack, alot of heat around the edges may help release it, but it won't be easy for sure.

Pics of the whole coilpack and the closeup of the connections for the tubes. You'll see on the end one how it is twisted (I did it for the pic), that is how the 3 of mine that had a problem looked when I got it opened up.

Thanks for the update and the pictures!

how did you know it was a clogged cat converter? Do you know what was the diagnosis?

I occassionally, like once in 6 months get a misfire code, but I'm thinking it's bad gas or switching between gas brands.

If I start getting it more, it might be the coils going.. but it could be the cat too, so I"m wondering..

maybe i should update my last statement... after 2-3 days from changing the cat converter the misfire started again.. so its still misfiring... i will try changing the coil pack for the last time ( 2 times allready ), i hope it fixes the issue...

to check the cat converter for being clogged, you can ither have the dealer check for you, or go purchase a (3-way back pressure tester) estimate $100 from a tool truck... once you have that tool you can fit the tool where the PRE 02 sensor goes. once you installed the tool just turn the car on and read the amount of pressure shown on the tool and refer to the specs shown in the instruction or OEM spec

The problem with a clogged converter is this: They don't "just clog up". If one clogged, that's usually indicitive of another problem.

Cat converter clogging is caused by misfiring! The spark doesn't happen, the fuel goes out the exhaust valve, through the turbo, and into the cat where it combusts as it hits the hot face of the cat brick. Enough misfires and the face of the brick starts to melt and close off the little squares, and then it's all downhill from there.

Hello, folks. Roadslayer here. Newbee and all that. I'll do a proper introduction in a bit.

On January 3, I purchased a 2003 S600 with 14000 miles on it. Drove it home from Houston to Seattle. Something I noticed is at cold start up and for the first mile I detect a misfire and roughness in the engine. After that all is OK. Naturally I'm hoping this isn't the dreaded coil-pack going out and would much prefer maybe a cold start device is malfunctioning. Any ideas would be appreciated.

Thanks. Roadslayer

Is it every time you start it or just a very rare event?
If it's rare, it might be the gas. Keep in mind which gas brand your using and what season your in (when they change blends). The blends probably changed from Houston to Seattle..


For me, I've been staying with one brand, one octane. I noticed a very rare misfire sometimes when I switched brands. It seems to like Shell lately, but I have switched to Chevon Techron which it liked also.