300E misfiring

its misfiring after just starting up

And then what happens?

If it continues to run, does it improve as it warms up?

after warm up its fine, about 5 minutes-thanks

TG, I also have some type of battery drainage problem....when the car is off the SRS light comes of once in a while and the windown still work, even with the key out... The battery is new....where would I begin to look for a problem like this?-thanks

Have you ever replaced the "over voltage protection relay"?

no tom.. thats never been replaced-chuck

The O-V-P relay is a mystery to me. It has a fuse on its top. It's known to cause strange engine behavior although I don't know why that occurs. Look for it and, for now, give it a light tap on its side.

To review: the engine runs well once it has warmed up. You've replaced most of the ignition parts. Have you checked the cold start system? If it's not working the engine will start cold only with difficulty and indeed need to be "warmed up" before the car can be driven for the air / fuel ratio will be too lean while the engine is cold and it will have poor throttle response - cough and sputter when you step on the accelerator.

We've speculated on the MAS (mass air sensor) and the O2 sensor. I'd set those aside from consideration if the car passed your state's emission test AND drives normally once the engine is warm.

I recall last year another owner had a similar problem - terrible engine performance when the engine was cold and warming up and suddenly, with a click, the engine ran perfectly. The over voltage relay was the cause.

So the suspicion is on the engine's cold start system and the over voltage protection relay.

To explain:

The OVP relay protects the sensitive electronic circuits, i.e. your ECU from high voltages.

It basically consists of a fuse, followed by a relay energised by a small circuit, which has a zener diode built-in. This relay feeds the the SRS, ECU and ABS (any others?). If the voltage goes too high, the zener conducts, and shunts the circuit to ground, cutting out the relay, and if very high, blows the fuse.

These relays get tired, as basically, it has to activate continously when the engine is running. 10 years +/- is about the lifetime.

When it cuts out, your engine reverts to "dumb" mode, and won't compensate for temp, O2, timing, etc.

Regards, WS

thanks for all your help, i truly appreciate it... i have a book by a guy named stu ritter and read the same thing about the OVP relay. I ordered a new one lastnite. This is a long story, but I will keep it short. I gave the car to my sister who is at college at rutgers, 27 miles away from out home and my school, monmouth university. The 300 sat for a few days, she claims she also left something on to drain the battery. She got one of her "college friends" to jump the car and she tells me now that he cross connected the cables. In Stu's book, it cleary states that if you cross connect the cables the OVP can take a long vacation. So i ordered the new one. I guess college doest not give you anymore common sense...lol

Anyone here ever change the cold start valve? -Thanks Tom and overyone else

This was a teriffic answer to the OVP question. I'd just install the relay and see if the cold starting is cured. It very well may be so I suggest you wait before touching the cold start system.

Tom, Rutgers '65

Thats where I will start. I appreciate it very much. What a small world....Someone here has some ties to my area...

SRS, ECU and ABS, that's all. And depending on model and/or # of systems that are protected, there are different versions of OVP relay, between 5 - 9 pins, and 1 or 2 fuses.

A cross-cable dur> To explain:

Hello Tom and averyone else.... I would just like to thank everyone who helped me with the electrical situation on my 300. I ordered the OVP relay and it fixed the problem. The car also fires up on no delay, and whats even stranger the car does NOT misfire at cold starts. Ill turn the key and it stays on. Since it was such a beautiful day here in monmouth county nj, i moved the car in the garage, changed the motor oil and tranny fluid/ filter, lubricated need parts and even waxed it.- Thanks, I appreciate it...Charles Grainger, NJ

Charles,

I am in monmouth county NJ as well. However, I am a mercedes Diesel owner. Tom Lambach has also helped me on this NG serveral times.

Anil

Well Charles, I'm glad to read it's finally fixed - mainly due to your sticktoitiveness.

Whatever will we have to talk about now??

Tom

Hello Anil..... Im in Spring Lake, attending Monmouth University. All of Monmouth County is fantastic...