colobart

I have a 2007 SL600. When starting in the cold (say under 50F) the engine runs extremely rough and I sometimes get a CEL. Scan reveals cylinder x misfire. Trying to drive it - even a little just to move it - is painful (limp mode, terrible sounding).

If I leave the car idling, the engine eventually warms up and then - almost all of a sudden - starts to run completely smoothly. From that point on it's golden; no misfire, lag, or loss of power.

Any suggestions/advice on what to look at first ? MAF, any particular vacuum line, some temp sensor ?

Advice appreciated !

Tom Manning

I would bet you have failing coil packs. They're a well known fail point on the V12.

colobart

Would they only exhibit an issue when cold ? Once warm, everything's perfect.

I don't get any DTCs from OBD - except for the cylinder misfires. What would show up in a scan if the coil pack was going bad ? (Besides a misfire )

Tom Manning

What scanner do you have? You need an MB specific scanner, a generic scanner won't do.

Scan with Foxwell or Launch CReader or similar and post up the codes for comment.

colobart

Just bought the NT510. Codes forthcoming.

Tom Manning

I don't have a V12 R230. Yet.

So I follow the discussions on the subject - this is the world expert on the V12 coil packs: https://www.v12icpack.com/

colobart

Tried out the Foxwell NT510. What a piece of junk. Sending it back to Amazon today.

I will try Launch CReader and see if it's any better. There are many models: is there one you recommend ?

Tom Manning

What is the issue with the Foxwell?

It's got the full MB package, but is very slow; I think they all take the same time to scan though.

If you get the Launch, please do report back, I'm interested in seeing a review of it.

colobart

Interface like a 12-year old wrote it. Wouldn't connect to two laptops. Wouldn't save results from a scan. Didn't even ID the cylinder misfire. Picked them up with another scan tool. I could go on.... but you get the point. I am an Electrical Engineer: I have somewhat higher standards for these types of devices; they need to be easy to use and highly complete and accurate. This device isn't either.

I ordered this one: "LAUNCH X431 Elite 2.0 Pro Bidirectional OBD2 Scanner Fit for Mercedes-Benz MB Sprinter Maybach, 2024 Full System Diagnostic Scan Tool, All Reset Service,ECU Coding,Key programming,"

I'll give it a run through and let you know how it goes.

There is something that's causing non-ideal fuel-air mixture when cold. Then all of a sudden it corrects. What component corrects so dramatically ?

I'd love for a scanner to help point in the right direction. Other than that I have to start diagnosing/testing/swapping any sensor that is in that decision making chain (i.e. IATs, MAFs, vacuum hoses, etc....).

Tom Manning

Not a semiconductor, they don't usually fail like that. Definitely get the full scan and codes and see where you are. Still likely to be the coil packs, why not contact the fella at V12icpack with your symptoms and ask him for any insight? He's a wizard. He's done youTube vids where he x-rays the coil windings. etc

Look forward to your report on the Launch. I agree the Foxwell has a very 1990s look and feel about it...

colobart

Good suggestion: I will contact the coil guy. Thanks for the details.

yovenim

I have a 2008 C30 T5 and I’ve had multiple misfire issues and they all seem to be fixed except for when the car is cold and starting for the first time. The car misfires heavily, the rpm’s sputtering from 900 to 2000 and everything in between until it warms up and then it’s ready to go. The misfire just goes away, I’m assuming the ecu just figures out the right air/fuel ratio while it’s warming up. I scanned the car and it says the misfire is on cylinder 3 so I tried replacing the coil pack, which is new, to the old coil pack but that didn’t seem to help anything. I’m wondering if it’s an air issue instead of an electrical but I’m no expert. The last misfire it had was due to a loose intake manifold so I hope this misfire is just as easy to fix. Thanks

tonylinc

The V12s it's important to have good spark plugs so I'll ask how many miles on yours. If near or over 40,000 miles I would replace those with new NGK Platinum Iridium. This may or may not resolve your issue but new plugs will help to keep your coils lasting longer before failing and needing rebuild. I agree that any V12 owner should read Clark's entire website.

MikeJ65

It sounds more like a fuel issue to me. On cold starts, the ECU will be open loop, it does not use O2 feedback to correct fuel trim. If you have a temp sensor error, low fuel pressure, or some other issue the open loop fuel mapping can be inadequate and there is no correction until it warms up and goes into closed loop mode.