C280 Poor Engine running after driving

[David C Klasse]

Problem first started yesterday after about 20 minutes of driving. I slowed to a stop light and noticed the engine was running very poorly... seemed like it was misfiring badly, shaking the whole car. I pulled over, turned off the car, restarted it, and it ran fine. Today, this has occurred about 5 times. Once starting the car, it runs fine... but after a short time driving, and coming to a stop, I notice the it not running properly. It is not only at idle... the engine runs poorly at all speeds, there is quite a power loss, and transmission shifting has harshened dramatically. No check engine light has come on or anything of the sort. I don't think it's the spark plugs, fuel filter, air filter, or anything like that... because it runs fine at first... and then suddenly begins chugging.
Any ideas? I hope it's nothing major. BTW, I have 110k miles on the car.
1995 C280.

[vinamg]

Have it scanned. There might be codes in there. I recall a similar problem on a 95 C280. The car did it only once during hard driving and no matter what I did I couldn't duplicate the problem. However, the computer stored an EGR valve fault. I checked the EGR valve and it was fine. I am still puzzled as to what exactly happened.

BTW, I would double check plugs for fouling.

Vin

[David C Klasse]

Yes, I was thinking that there might be stored codes in there. I might try unplugging the battery, to reset the ECU, and see what happens. It seems as though it did start the rough running after hard driving, and today start the rough running after hard driving. But there were times when I would just have started the car, pull out of a parking lot, step on the gas, and it would run rough. It only does it though once the car has been driven for a while... as in, it doesn't seem to do it first thing in the morning after a 50 mile drive... but later in the day, after the car has been driven for some time, it will do it... I say this because it has not done this at all tonight... but I haven't been driving much... so I don't know, we'll see, I will take it in tomorrow to have the codes read... thanks for the advice.... any one have any more?
I'll post back with the results.

(I haven't been online much because my WWW [IE, AOL's IE, or Netscape], on my computer has not worked. So I have to check websites either in the computer room, at work, or where ever else!)

[mbdoc]

David, on all of the HFM(efi) engines the injectors can be shut off if the ECU senses excessive misfire to protect the Catalyst. Sound as if this is happening to your engine. Some one will need to scan(live data) while this is happening to see just what the problem really is.
Injectors will start again on engine restart until the misfires happen again.

[David C Klasse]

After doing a search, I thought of one more thing. I do hear a popping sound many times when I step on the gas. COuld this be a lean pop? I thought it was some drivetrain mount... but inspection showed nothing out of the ordinary (flex disc recently replaced)... I thought they overlooked something.
So it might be related? Is the lean pop always audible?

[David C Klasse]

Ok... I observed some more characteristics today.
The fuel injectors turn off when the engine is revved high (driving hard). If I drive very slowly and keep the RPMs below 3000 (probably good for me ), then the car will not act up.
But when I step on it, I hear a POP (which I thought was still something in the drivetrain), and then immediately the engine runs like crap... /the injectors shut off.

So it seems to me as though I am getting a very lean POP which turns off the injectors to protect the catalyst.
Now, because of the lean POP, I get the misfire, which is really what is turning off the injectors, correct?

Shouldn't the ECU adjust accordingly by itself? What do you guys think I'm looking at?
Thanks a bunch guys.

*engine not revving hugh until problem resolved*

[Stan Pittman]

If you have codes it should be P0170. Have the actual values checked with a scan tool and check the self adaptation for the air mass sensor. It should read 1.0 if not check for bad vacuum leak or bad fuel pressure regulator. Most of the time hesitation is a bad air mass sensor.

[David C Klasse]

THanks for the insight Stan. I am taking the car to the dealer shortly to have the problem checked out.
What about plug wires? I know they should be changed at 100k miles.... I do have 110k miles on it now...
Will keep you guys posted.
Thanks.

[Jason Beal]

Hey, I'm curious...what ended up being the problem with your car?

JJ

[David C Klasse]

It ended up being:

The plug wires
The coil ends (X3.. [2/cylinder])
& The Spark Plugs.

All of those were pretty worn, with the worst being the plug wires, which are supposed to last about 100k miles.

All in all it costed about $150 parts (dealer) and about an hour and a half of labor.