wammer23

My 1996 C280 will misfire everytime I "punch" it at low speeds only. When I'm traveling between 10 and 25 mph and I accelerate sharply I can hear the engine misfire and the CEL light comes on. Most of the time it's cylinder #1 that's misfiring although one time it was #5.

When I'm on the highway doing say 50 or 60 mph and I floor it the car downshifts like it should and takes off like a rocket. It runs great.

Relevant Info:

about 1200 miles ago I changed from the stock copper spark plugs to Bosch Platimum +2's. Could this be the problem? I did replace #1 a second time to no avail.

I tried disconnecting the MAF and test driving but the exact same misfire occurred.

The throttle body has been cleaned recently and is not dirty.

I'm going to do an OHM test on plug wire #1 to see if maybe it's bad.

If it's ok, do you think I have a fuel delivery problem?

Thanks!

LawRens

I would like to believe it's your coil packs going bad. If your coil packs go bad, it may trickle down to your spark plugs. The same symptoms happened to me too a few months back on my c230.

austin814

The problem is the spark plugs, the L6 in the C280 should only have Bosch Copper Core plugs. If the coils were the problem then you would be getting a problem on more then one cyl because the L6 shares one coil for two cyl. I have a 96 C280 with 233K miles on it and change the plugs yearly. I have never had a coil problem.

wammer23

Just replaced the broken vaccum hose but the misfire is still there.

I put the old copper plugs back in and went for a test drive and still no luck.

It seems that the misfire is now showing up in #5 and #1. I don't think it's the coil packs either because 1 and 5 don't share the same coil.

It's so frustrating! The car runs awesome at high speeds but misfires every time I give it any significant gas at low speeds.

Any thoughts?

austin814

I would switch the spark plug boots on Cyl 1 to cyl 2 and see if the problem moves with the boot from Cyl 1 to Cyl 2. Also make sure the boots are on tight, sometimes you have to press down hard to make them pop down onto the spark plug. Also make sure the plug wires are nice and snug on the coils. Dont lose faith, the M104 is a wonderful engine when you learn how to take care of it. Mine has 233K miles + 50 per day. It also wouldnt hurt to order a new pair of copper core plugs just to make sure that isnt the problem. I always order from mercedesshop dot com but any MB site should have them. To keep it running smooth I suggest new plugs every spring and new air filter every 7K miles.

wammer23

today I switched places with the coil packs to see if the misfire moves. it didn't still in #1 or #5.

I tested the fuel pressure it was 48 psi at key on engine off. it was 48 psi while engine on and idling. it would surge to around 54 psi or so when i revved the motor.

I removed the EGR valve and cleaned it but no change.

The car just seems to sputter when given gas at low speeds.

ANY THOUGHTS? PLEASE!

austin814

In troubleshooting a misfire start with the least expensive part and work up. Replace the plugs with Bosch FR8DC+. The Platnium, +2 or +4 plugs will make the M104 run badly. If that doesnt work replace the plug wires. Use Bosch plug wires, for the M104 that should be around $70 and like replacing plugs is very easy on the M104. Replace the spark plugs and let us know.

wammer23

if you'll read my earlier post I switched back to the standard bosch copper plugs and there was no change whatsoever.

I OHM tested the wires with my multimeter and they tested good. I don't want to replace parts just to try it. I don't want to just keep replacing parts till I get the right one. I guess I'll take it to my indie and have him scan with the SDS to find the issue that way. Thanks for the help.

austin814

I suggested new spark plugs because I assumed you were replacing them in the first place because they were old or had a problem? My assumtion was that going back to them wouldnt help in finding the problem. If there is a misfire its pretty basic and I would certainly spend the $15 for new plugs before spending $50+ at an indie shop to diagnose the problem. You have to consider spark plugs are a maintenance item so replacing them is not a waste of money. Just my 2 cents! Good luck and let us know how it goes.