Hello, today i tried to replace the spark plugs on my 1995 E320. We were told to get the Bosch Platinum 4+ (the only kind everywhere has), so we replaced the original ones(1 tip) with these platinum ones(4 tips). Then when we started the car it was shaking very badly as in running with 5 cylinders(cannot confirm). So we thought replacing the original ones would work. After putting the old ones back in, the problem did NOT go away. Though twice the engine ran fine, but that never happened again. Since we were only trying to replace the spark plugs we did not touch anything else. Does anyone know what the problem might be? Thanks for you help.

outie,

In the process of pulling the spark plug wires, you may have inadvertantly damaged them. That's the simplest thing I can think of. Hope that helps.

Nolan

Thanks. So is there a special techique to pull the wires? If so I do not want to damage them again next time. Thanks again.

Are you certain that you didn't cross switch a couple of the wires when replacing them?

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Ted
1979 240D
160,000 miles

Yes i'm pretty sure because we did it one by one. (replace spark, then put the wire back. next cylinder)

When removing the wires, twist the boot back and forth until it comes loose, and don't pull on the wire. I don't know about the '92, I believe this is a twin cam motor, but on the single cam engine, the boot or terminal can be replaced without replacing the entire wire.

Good luck,
Larry

This car has the M104 motor. The plug wires usually pull off easier than those on the M103. If this car has the same ignition system as my '95 C280, with the coils in the valve cover, the wiring harness might be suspect also. Look all the wiring in the valve cover area.

Thanks for the replies. I will try again later today. By the way when my father tried to start the engine again last night, it wouldn't start up anymore -_-

Maybe the wires are having problem?

The plug wiring routing diagram is on the valve cover. I would check that first, then look at the connections on the coils. The inside plug cap in the coil tower on all 3 coils should be cleaned before plugging them back onto the plugs.
Also, as stated in earlier post, look at the wire harness . They were famous for shorts and bad insulation problems.

PS-
The 104 calls for F9-DC0 Bosch copper plugs.
That has beeb replaced with Bosch F8DC-4.
Also copper. You may have trouble finding them as the stores are all pushing the plats, but you want copper on that engine.
Parts Shop has them.

What you describe might be an engine wiring harness problem. If the coil power wires have the insulation falling off of them, this can happen. Search "engine wiring harness"!!

Pull off the cover again and make sure the coils are grounding properly. You have to watch when you put them back on to make sure the ground post makes good contact with the coil.

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Rgds,
Aaron Greenberg
MB technician
Precision Motorcars, Cincinnati, Ohio
'67 250SE Cabriolet
'77 450SL
'80 300SD
'85 380SE
'86 420SEL
'89 420SEL
'93 300E 2.8
'74 Jensen Interceptor Mk.III
'81 DeLorean DMC12
'84 BMW 745i Turbo

As it turned out, the problem is from the set of wires coming from the computer to the rest of the car's sensors. The wires are all decayed when cut out. So I guess it's not related to the spark plugs, but it triggered the problem.

Thanks for all the replies.