resistro

1998 S320 w/93kmi, misfires under load. But when I restart, idles normally till i drive about 20 feet. Check engine light on and im getting p0300 (random misfire) p0303, p0304 (3,4 misfire). No other codes.

1) Already swapped coils from different chamber, no help
2) Tried different plug wire for the number 3, no help
3) Swapped plugs from different chambers, no help
4) No oil or water anywhere and the chambers look good

Why the heck is the computer shutting down the coil for the 3,4 cylinders when the car is under a load? When i pulled the plugs the looked pretty good, maybe a tad lean, but looked perfect. Could the computer be shutting down the coil because of a lean mixture somehow? I have a snap-on MODIS scanner but I am using the generic OBD configuration and i can't hardly pull up any other info besides the codes.

resistro

Fixed the misfire. I finally figured out what was wrong.

mleskovar

What was it???

brakel8

Isn't that nice! Ask for help, then tell us you fixed it, and not share what solved the issue?

resistro

I really dont know exactly what fixed it but, I replace plugs and ran fuel injection cleaner and it seemed to do the trick. so maybe it was sticky valves and the cleaner helped. But now, when its cold, if I floor it it will miss like crazy. Maybe cause I got the cheapest plugs i could.

hineywineries

You are driving one of the last of the finest cars ever built ( I wouldn't go past 98.), and you put cheap plugs in it. I think you should trade it for a Chevy Cobalt which isn't a bad car by the way. I rented a couple of them in Hawaii last year. I found it to be superior to the PT Cruiser I rented on the big island.

paulv

PCM's tend to shutdown coils and injectors when there are excessive misfires to prevent raw gas from going into the cat convertor. Can you read any Mode $06 or any freeze frame data with the MODIS on your car? Long term fuel trim (LTFT) values that are out of wack can help you diagnose -- e.g., for misfires, LTFT values that are less than +/- 18% (approx) tend to indicate an ignition problem while above that value tends to indicate injector (dirty or faulty) or mechanical problems (burnt exhaust valve, for example).

Regards,
paul...

resistro

The car still misfires BAD when its cold, I can floor it and it won't go anywhere, not as bad when it warms up. I put the expensive BOSCH plugs in and no help. No CEL I took pics of the trim values...I will post them shortly.

mleskovar

Did you try unplugging the MAF and see if it runs OK? If it does, 1st try cleaning the MAF.

resistro

I did try to unplug it, when I did, It almost stalled for a sec but continued running the same. No CEL came on either. It didn't help or hurt. I did use that CRC MAF cleaner, no help. I also checked the output DC voltage (the MAF and IAT outs) of it on the scanner (per ALLDATA output specs)-all perfect. I also saw no glitches on the graph. But, this is the same symptoms (along with wierd transmission shifts) everyone else says its a MAF issue. Should I try to replace it anyway?

mleskovar

When was the last time the fuel filter was replaced? I had very intermittent 'stumbling' that stopped when I replaced the fuel filter. I also cleaned the MAF at the same time so I don't know what really fixed it. Maybe the increased fuel needs while cold isn't being met.

mleskovar

I just read this again. Try unplugging the MAF before you start motor. Any difference?

resistro

This is what my scanner is showing at idle: can anyone tell what looks bad? the only thing I saw out-of-spec was the throttle valve angle at 3.1@degrees.


http://s671.photobucket.com/albums/vv72/resistro/

Runninrebel211

I had this knocking problem on both my S classes. 1993 300 SE and 1990 300SEL. It was bad gas at a 76 station that I filled up at on Millbrae Ave in Millbrae, CA. They didnt change their pump filters and I should have known to stop when the pumps are very slow at filling the tank- a sign of a clogged filter. Have to keep topping off gas with Shell or Chevron and octane booster and fuel injector cleaner. Almost fixed but still slight knocking.
Do you remember where you last filled up when knocking started? Dont fill up there anymore. Complain to management that they need to change their pump filters and if they give you lip...call the company and let them know.

resistro

I checked the fuel pressure and it was right where it should be. I even unplugged the fuel pressure regulator vacuum and the pressure jumped up like it should. When I changed the plugs I noticed that the old plugs looked a little lean. I just ordered a new Bosch MAF-I hope that's what it is.

resistro

I CAN'T BELIEVE IT! IT WAS THE MAF!!! What I thought was a trans issues because of a hard shift was an engine misfire issue all along. I guess I thought it was the trans because it shift hard over 3K RPM. But the motor starts its power band around there. So actually what was going on was since it was misfiring over 3K RPM and had less power, (I bought the car with this problem) I couldn't' notice it was missing because I thought the power band was flat and the trans was just shifting hard. But the trans was doing its job at that RPM. THIS THINGS RUNS SO MUCH BETTER!!! EVEN AT IDLE!!!

TMAllison

The person who helped you resolve your problem (on another forum) is one of the top techs in the nation IMO.