124 Distributor Cap Replacement

[uberwagon]

My '88 300TE started running rough after warming up. It quickly got worse and now does not even start.

I've been reading though the many threads with similar problems. It appears to be an electrical issue (plugs are black and dry). Checked the coil and crank angle sensor resistances and some basic voltages I can measure with a multimeter. Since I had a new cap and rotor, decided to replace those.

After struggling to get the cap off (following someone's suggestion I cut off an allen wrench and used it in a socket to get off the bottom bolt) I found things didn't look too bad but contacts were black and green and looked pretty fried.

To (finally) get to the point, I found there was a black "gasket" behind the cap that was split as shown in the picture. I put gasket in quotes because it is very hard. The question is, what should this gasket look like? Should it be hard and split or do I need a new one? The cap gaskets I've found online are orange. Is that the right one?

Thanks,
BoB

[Jackd]

You can find the ''O''ring here

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1ZX0L3NOG1ZY15MPW6&year=1990&make=MB&model=300-E-002&category=F&part=Distributor+Cap+Gasket

[cjlipps]

Bob, the 0-rings I got when ordering new have been orange. Just get the cap, rotor and o-ring and replace the black brittle one with the new orange one. It looks like your backing plate is ok. You don't mention how long the existing cap and rotor have been in place. I'm a relative newbie here but it seems like these 103 engines consume caps and rotors at a high rate.
Chuck.

[uberwagon]

Thanks guys. For all I know, the cap and rotor are original. I'll order a new o-ring to go with the new cap and rotor. Hope that gets me going again.

BoB

[softconsult]

Sort of surprised you got no response to your description of plugs as being black. My experiences with M103 and M104 engines is that proper electrode color is more brown/grey. The pro mechanics may have some input.

Steve

[Ferdman]

Bob, be sure to replace the spark plugs too. Dry black deposits on the spark plugs would indicate that the fuel mixtue is too rich ... if black and wet it's likely time for new valve stem seals.

[uberwagon]

Plugs were tan in color when I pulled them last summer while tracing what turned out to be a faulty fuel pump relay. I'm assuming the plugs are now black because of failing ignition.
BoB

[softconsult]

If it were me, I would also put in a new set of plug wires.

Steve

[uberwagon]

Just wanted to post how this turned out in case someone else is trying to solve the same problem.

The car started stumbling a little when warm. Within about a dozen trips, it was barely running after a few minutes and finally would not start. I checked a few other things and then decided to replace the cap and rotor since I already had new ones. Had some difficulty getting the cap off (see http://www.peachparts.com/Wikka/M103TimingCoverReseal for tip that worked for me) and got a new distributor cap gasket on advice from this forum.

Long story short, put the new cap, rotor and gasket on this morning and she fired right up! Once again I have to say what a great asset this forum is. Don't know how I could keep the Uberwagon running w/o it.

Thanks,
BoB

keywords: 300e