overboostTSI

Ok guys heres the deal. My dads 1990 300e I-6 3.0 with about 180k miles, has had this weird misfiring problem every now and then (it would basically foul one of the spark plugs really bad), this seemed to happen especially when the car was sitting in traffic for extended periods of time. A few weeks ago, after i filled the tank up from this local gas station that is notorious for having crappy gas, the car is running the worse ever. I have filled the tank since that time 3 times full with 93 octane and the car still runs like crap. It seems like it misfirring, when you press the gas it bogs and stumbles and doesnt want to move. The car sounds like its choking, but the funny thing is that sometimes the problem will go away(usually warm engine) and the car will run like it was brand new. The car doesnt foul out the spark plug anymore either.

I replaced water pump (leaking bad), spark plugs and wires, all new injectors, fuel filter and air filter. The cap and rotor were replaced about 1-2 years ago. Timing was checked at idle (10 deg.)

Like i said the problem will go away all of the sudden and the engine will run like new. There is no check engine light on. Is it a vacuum leak? or something else?

Thanks for the help.
Dan

BrabusCClass

How is the compression on the motor? Maybe your motor is just bad or your seals could make it lose compression. How is your distributor? I had misfiring when there was something wrong with an electrical harness. It blew up my wires and caused my spark plugs to spark too much. I had the harness replaced and then my wires and plugs. Then it was ok.

Renok7

Could it simply be that you have water in your gas tank?

overboostTSI

Hey thanks for the reply. The compression was fine but a little lower in #4cyl then the others but by less then 10% diff. . The problem seems to be intermittant though. If the car is not bogging or stumbling it runs like new, it just seems like the car is choking or something. The distributor cap and rotor was changed maybe 1-2 years ago.

overboostTSI

YOu know thats what we have been thinking, but we have gone through 3 full tanks of gas since then and its still the same. When i pulled the fuel filter out I poured the gas into a glass jar and let it sit for a while and didnt notice any seperation in the gas to show there was water in it. I think tonight I will syphen some gas from the tank and pour some gas into another glass jar just to verify.

Renok7

Have you tried adding a bottle or two of STP gas treatment to your tank? Trying to siphon water out of the tank may be tricky as it will collect at a low point.

sosh

Saw a similar problem with a friends earlier E300. It was the fuel injection system that needed a complete rebuild. Was very expensive at the dealers but warranted when done. Actually he spent less at the dealers than he had over a period of time trying to correct it at independant shops that did not correct the problem. His E now has 260000 miles!! Runs great.

overboostTSI

This morning I started the car outside in the cold, idle was fine and car bogged just a little bit but it went away as soon as the car warmed up completely (drove for 25 min.), parked and went inside for about 10 minuntes, came back out started the car and it ran like crap for about the first 5 min.(the usual bogging and stumbling, coughing) then it ran perfect for the remaining 20 min. drive back. Parked the Benz in the garage. 2 hours later came back out, started the car and the idle was terrible, reved the engine a few times but it was coughing and having trouble revving. So I just shut it off and took the talon to the store.

I was gonna stop and get some gas treatment when I was driving the Benz, but on the way home the benz drove perfect so I said to myself, " I think the car is ok now," Oh how wrong was I.

Thanks for the replies guys.

Dan