Nardulli

03 S600, 70,000 miles, well cared for car

Problem began with slight mis under highway speed acceleration. Backing off throttle a bit would eliminate the miss.

Gradually became more prevalent bit always under moderate to heavy acceleration. Backing off throttle solved it.

Normal driving and idle seemed perfect.

Last night attempted to pass on freeway, serious misfiring And this time was persistent. Limited to about 65 mph. Any load on engine produces misfire.

Significant loping now at idle. Check engine light now on.

I didn't suspect spark due to intermittent nature of problem, suspected fuel delivery issue. Now i am not so sure.

Mass air flow fault?

Is there an aftermarket tool that I can use to read the codes generated?

Spark plugs replaced 2,500 miles ago.

Thanks to all.

biker349

possible coil pack.

Nardulli

so, next morning I drove the car, and it appears to run normally, although I did not attempt WOT acceleration.

TMAllison

Why guess? Get a $50 OBDii scanner and read the code.

Nardulli

I was under the impression that a standard scanner would not be useful with the Mercedes. Glad to know it if this is bad info.

Nardulli

Hi All,
Codes PO 300; 303; 308; 310

Misfiring on Cylinders 3, 8 and 10.

Not much to go on... anyone have additional thoughts?

Thanks.
Jim

theunderlord

Swap Coil Packs from the cylinders that are OK ( 1,2,4,5,6,7,9,11,12) to the ones that are throwing codes (3,8,10) (any 3 will work)

Clear the Codes, start the car, drive it around the block, when the Codes come back, check them and see if you get them on cylinders other than (3,8,10)

If you don't get codes for 3,8,10, the coil packs are probably the issue. If the codes are the SAME as before, it might be the plugs.

Nardulli

Thanks. Tried to erase the codes, but the low cost scanner I have just through an error. anyway... these monsters are fun, eh?

theunderlord

You got it. While you're in there, it might be a good idea to have some new plugs on hand. if the car has been misfiring for a while, the plugs are probably toast as well.

Any auto parts store will read and erase your codes for you for free too. (you're going to have to get them erased right before you swap a bunch of stuff, otherwise you'll never know if it helped.)
--- also, you might get some more responses if you put this in the S600 subforum.

Nardulli

Damn, I just replaced the plugs 2,500 miles ago. Bleh...

benzmodz

I believe it may also be the dreaded head gasket syndrome.

biker349

if the codes stay the same after swapping coil packs it could be the throttle body.

Nardulli

the codes show a misfire on cylinders 3, 8 and 10. So, one on left bank, two on right bank. Would be strange to have both ignition modules fail at teh same time... I erased the codes. The car seems to be running fine. But, I have not driven it extended hiway since the last episode... I am beginning to suspect a sensor. But... which one? Yikes.

benz_addict

Common on these engines. Very sold engines, no head gasket issues I ever heard of.
I gaurantee it's either one of the two coil packs.
Do not listen to the swapping coil pack advice, as these cars have only 2 coil packs. They are not interchangeable.

Your problem lies either on the ignition module, or the coil pack it self (controls 1 bank, 12 plugs per side)

Not to say the least easy fix, but very expensive.

Good luck

Nardulli

I've got misfires on both banks... So that would mean both coil packs went wrong at the same time... I've reset the codes. When it happens again, I will be able to see if it is the same cylinders.

I've found the coil packs for $990 each. Ouch.

BBBSS

Aren't you glad you don't have 12 now???


Yeah, yeah I know.

Nardulli

So, the saga continues. Recap: Car runs normally under mild acceleration. Smooth, etc. Can achieve speed if engine load is kept low. On hard acceleration, the car misses. If I don't back out of the throttle right away, it will throw misfire codes. Cylinders misfiring are not consistent and are on both banks of engine. Spark plugs are replaced 2,500 miles ago. Car is pristine, always well maintained. only 70K miles. Unlikely that both coils went wrong at the same time. Ideas?

biker349

short in throttle body, or fault in accelerator pedal. should throw a code.

shardul

iTrader: (1)

it is the coil packs. i have seen cars on which both go back at the same time. time to spend about 2000.

biker349

i had the same exact codes as you, along with a code for the accelerator pedal. the dealers tech checked the coil packs and even took out spark plugs to check. all was fine. finally figured out that there was a intermittent short in the throttle body. replaced accelerator and throttle body and all is good. the coils are a known issue, but so are the throttle body and accelerator. hope you get it sorted out without changing multiple and good parts.

Nardulli

I assume you mean the throttle position sensor when you write "accelerator"?
I'm used to mechanical throttle bodies. Is this thing electronic? Yikes. Ever long for a carburator?

shardul

iTrader: (1)

Yes it is an electric throttle body

biker349

the accelerator pedal is electronic as well. you better find a good honest mechanic, or get a mercedes repair manual or you are going to spend a fortune on replacing parts!