distributor cap and rotor service
 

How do you know (visually)when to repair or replace a distributor cap and/or rotor? Can you clean/service either without replacing them? I realize they're relatively cheap, but I don't know how old the ones on my new-to-me used 1992 190E are and I don't want to spend $70 if I don't have to. The issue my car has is it seems down on power. Spark plugs and wires and compression check all show good.

pull it and see if it looks good.... contacts should be clean.

does your 190e have a 4 cylinder engine? they don't have much power...

should have more than enough if you have the 2.6

If it looks like this
http://www.peachparts.com/shopforum/attachments/tech-help/10596d1060551590-thanks-steve-you-nailed-one-cap1.jpg
you need a new one.

I have 2.6. It feels like a 4 cylinder.

Aside from cleanliness, also look to ensure that all the angles are still sharp and not irregularly shaped.

The distributor cap in that photo is nasty! It looks like the rotor went bizzerk and sprayed electical charge everywhere.

If I ever have my cap off, I check for buildup on the contacts and scrape it off - just like we used to do with the old engines w/points. If there's ever any roughness on the end of the rotor, that can be smoothed down w/a points-file.

I had two which looked as bad or worse than Pete's illustration
 

95 S420 119 V8 motor has two caps and rotors. I cleaned and with 000 steel wool and filed the rotars flat and clean, then sprayed the inside of the caps with circuit board "conformal coating" of the type like printed circuit board are coated with. That was several years ago at 60K. I am now at 120K and have never had them opened since. I did replace the spark plugs at about 90K but did not open the caps again. Seemed to lengthen the service interval some. If the caps have any cracks in the body of course they must be replaced, but cleaning and coating seemed to work for me. Original 12 year old caps still being used. DanielW

Does this look like normal wear and tear...

http://i243.photobucket.com/albums/f...anza/rotor.jpg

http://i243.photobucket.com/albums/f...stanza/cap.jpg

I would replace the rotor and cap in those photos, it does look normal, nothing bad about it, just time to replace.

The HEI ignition system is so powerfull that the rotor can short to ground via the distributer shaft, causing all sorts of backfires through the intake and exhaust.

I just had that happen on my '84 Vette, a new Accel cap/rotor($26.00) and some Delco plugs(18.00) later and it runs great. What's not great is that itt blew out the right side collector gasket when it backfired, drat.

I can't let mine go that far. Wish I could....I have two, and they're not cheap.

(anybody have some cheese to go with my whine?)

Costanza, the distributor cap and rotor are in really poor condition ... long overdue for replacement in my opinion. I replace the distributor cap, rotor and spark plugs every 30,000 miles in our 124 cars. With the price of gas today it's best to have an engine running at peak efficiency.

Thanks. I did replace with a new set I picked up on eBay for $50! I don't notice the car running any better, but I guess I feel better.

costanza, I recommend replacing the spark plugs also, and make sure they are gapped correctly. How did you conclude the ignition wires were fine? If they are original it would be a good idea to replace them too. Use Beru or Bosch ... whatever brand/style is in the car originally ... you may want to call your local MB dealer and check what style ignition wire set they sell for a 1992 190E.