BrianinLR

hey guys, ive often come to this thread for help and i am thankful for so much useful info here. i have searched and searched for help with this problem: january 2011 i quit driving car - got company car. started it some to keep batty charged, etc, but no miles. have always run premium fuel, and it had a half tank. 2 weeks ago, i get in to start driving. running rough. topped off with premium, drove 30 miles hard, still rough. added seafoam to fuel, changed fuel filter, drove another 60 hard miles. still misfiring on 7 and 8. but only after it has been running for 2-3 minutes (not even warm!) this morning i started it in driveway, and it ran perfectly - for 3 minutes, then it starts again - cant even inch out of my driveway.
i dont see how it is plugs or injectors, etc, when it runs fine for the first 3 minutes. i can drain the fuel, but again, why would it run fine and then go bad? when i parked it, it was running just fine. i was thinking fuel or fuel delivery, or plugs, but again, the first 3 minutes of running perfectly has me in a state of WTF. any help is greatly appreciated.
(if this has been addressed previously, i missed it - sorry.)
Brian in Little Rock, AR -
97 E420 with 205,000 miles (170k put on by me) -

C43AMG

MAS or maybe a bad coil pack is my guess...although a bad coil pack normally throws a code.

RichardM98

Your car has a built-in diagnostic system. Borrow or buy an inexpensive OBD scanner and check the error codes. Post them if you want help with the interpretation.

BrianinLR

i had the codes read last weekend and it was showing misfire on 7 and 8. will have them read again tomorrow and re-post.... thanks. brian.

RichardM98

I can't tell for sure but are you driving the car? If so you should erase any pending codes and see what returns. If you haven't erased the codes from last week they'll still be present.

What were the actual codes? Should be a P followed by 4 digits.

FYI - since you have dedicated coils and plugs on each cylinder a bad coil is unlikely but one thing that can cause adjacent cylinders to misfire is a head gasket leak.

CA_Tallguy

I've dealt with this type of symptom in my E420. It was a bad ignition coil. You can trouble shoot the ignition coils and spark plugs yourself. As others have said, GET A CHEAP ODBII code reader at sears, harbor freight, online.. whatever. Makes it much easier as troubleshooting is basically swapping coil packs and spark plugs with other cylinders to see if the problem follows. So, you say you have misfires on 7 and 8. Well, start by swapping coil pack on 7 and 6 and see if you get a misfire on 6 after the move. Then do the same for 8 and 5 or whatever. And then if problem persists, try spark plugs. This is all very, very easy to do and quit satisfying when fixed! This sounds like exactly what I saw happening with my bad coils so I'd start with those. You might want to search the forums for more info on the coils as well. Seems like they are prone to getting wet or fouled or something.

CA_Tallguy

Just remembered a few more details -- the second time this happened to me, I'm not sure WHAT happened in the engine but the car was almost totally disabled by the problem. I limped to a nearby mechanic to get it looked at and there was definitely a bunch of fluid fouling the coil packs. I seem to recall that he was able to clean out the fluid and dry them out and they were then OK. I hate it when problems like that come up though as it is best to fix the problem that introduced the fluid so that it doesn't happen again. I don't think we figured that part out.