Here are some questions I have about the distributor cap/rotor in the M103 engine (300E): Is the distributor cap removed when the head gasket is replaced? I've got a minor miss at idle after the head gasket was replaced. Otherwise the engine runs perfectly. Is there a recommended mileage where the cap and rotor should be changed? There seems to be a lubricant that is used with the cap/rotor. How is this used? Is there a Web Site where servicing the distributor is discussed? Thanks in advance, Bud

1. Yes. Was the slight miss there before the head gasket replacement? 2. I've seen OE caps and rotors last for over 100K with no problems. Inspect them periodically. 3. Lubricant??? I'm not sure what you mean. More info!

There was no miss before the head gasket change. The car has 56K on it and the dealer that did the gasket change has an excellent reputation and was told to replace anything that needed it. All that was found was a bad flex disk and a cracked serpentine belt.

Everything else was fine.

The plugs and wires are new. The miss only occurs at dead idle otherwise the engine runs as good as new.

The lube question came about because Fastlane and others sell something called Distributor Cam Lube.

I suppose I could take a look at the distributor cap and rotor but since the dealer didn't find any problem with it I'm not sure it's worth the trouble.

The only other thing possibility might be damage to a plug wire.

Bud:

Distributor cam lube is used on old distributors that use points and condenser. This would not apply to your 103 motor.

If you paid someone to do the work and you're experiencing degraded performance afterwards, have them review the work and solve the problem.

On a side note, the resistor tip(part of spark plug wire that attaches to spark plug) can be easily damaged on removal. Depending on how often the plugs have been changed, they've been yanked off at least that many times.

It's possible one of the resistors has slight damage. This is but one of many things that could be causing the slight miss.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

Thanks Mike,
I'm beginning to suspect a plug wire. I will call the dealer about the miss.
Bud

Bud,

Just to clarify Mike's point, 99.9% of the time, the problem is not the wire, it is the connection between the wire and its resistor boot.

If fact, Stevebfl has posted many times that any time his shop replaces the spark plugs, they always replace the resistor ends, too. The connection is just that sensitive.

The resistor ends are about $7 to $10 each...

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

I'd replaced the entire wire set just before the head gasket replacement. I guess I should look at the old ones to see how the resister boot comes off.

BTW, is it feasible to test these wires with an Ohm meter?

Bud:

What I'm about to say may be wrong, but having looked down inside of these resistor tips, I've got a feeling that an ohm test "might" pass in a resistor that was slightly damaged.

Perhaps we will get clarification from one of the pros.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

Do you mean you have a single cylinder miss, or a rough idle.

If you have a rough idle, this may very well be spark plug related. Did they replace the plugs? The factory calls for, I think, .038 gap on standard, not platinum plugs. Use standard plugs with a .035 gap and there will be a noticable idle quality difference. The platinum plugs have a very thin center electrode that gives a thinner spark.

Good luck,