What causes this to happen to a distributor cap?
 

Been having hard start issues on both cold and hot engine.car never ran rough, just hard start, idle is really smooth. Took off distributor cap and saw this. Cap was replaced 6 months ago, plugs maybe 1 month ago, rotor 6 months ago, wires 3 months ago maybe. (I replace parts on my car often for peace of mind and because I have warranty.)

engine ground strap?Coil,inferior materials in cap.

Ismalley, is there an O-ring on the distributor base? It looks like moisture is getting inside the distributor. Are the distributor cap and rotor Bosch brand? How old is the coil?

Hard start issue could be due to leaking fuel injectors that bleed off fuel when the engine is turned off.

O ring was in place. Everything was Bosch brand except for Champion plugs (though I highly doubt the brand would have anything to do with this), all fuel components from the fuel pumps to the fuel injectors are new (less than 1 month old). Plugs look brand new, they are only slightly brown and have zero carbon or any other type of build up. Could a faulty ignition coil or ezl cause this? I replaced the cap yesterday as well as my alternator (again, not throwing parts, just replacing because I have these on hand and get them replaced free), but I'm worried that there may be another issue causing it and don't want to fry this one. I do have an extra ezl and ignition coil on hand too, but as I've said the car runs incredibly smooth with no hiccups in idle and I'm not sure if a hard start issue would be failing symptoms of the coil or ezl. I think I read somewhere that when those components fail then it is total failure and the car won't even start or run. I could be wrong though.

I run extra ground straps on both my cars.One from negative terminal to block,and one from body to block.

wrong gap on plugs and/or too much resistance in the wires. my clients don't get bosch wires or champion plugs. beru or karlyn wires and oe bosch plugs when available. if not, ngk. good luck, chuck.

Is there any oily residue under the cap? If there is it may be coming from the camshaft seal.
Is the large oring seal for the cap still soft or hard as a rock and cracked? I had to replace mine many years ago.
Are those Champions resistor plugs?
How bad is the rotor?

Rotor isn't bad at all except where the center part of the distributor was fried. The Champion plugs are non-resistor with solid copper core. O ring on distributor was brand new and still soft. Cam shaft seal was replaced the same time I did distributor 2/21/16, so less than 6 months.

The spring loaded carbon button in the center of the dist cap is burned away.

Was the cap fully seated?

Is the bolt pattern such that it can be rotated 180? If so there is usually a tab that prevents the cap from seating when 180 out and perhaps the cap was pulled away from the rotor allowing the button to lose contact with the rotor.

The stuff on the terminals looks like grease, did you add something to them?

Cap can't be rotated. But the grease you are seeing is dielectric grease from a dirty rag I used to try to clean up the cap. I didn't want to use any chemicals or cleaners inside the cap, but after seeing the amount of damage it wouldn't have made a difference what I used to clean it with because it was toast anyways, just thought that I could've salvaged it if it was just dirty

Very hot spark...think outside the cap. Coil as has been mentioned. Is your alternator regulator ok? Have you installed solid core wires? Have you installed some sort of wire organizer?

I had the same issue, although my caps were burning every year. Swapped in a good used ignition coil and things went back to the normal 3-5 year interval

Brand new 120amp alternator installed yesterday, before then alternator was replaced in 2012, but vr was swapped out every year. Actually, with my spark plugs, I am running non-resistor Champion plugs that I converted to non resistor plugs by removing the resistor and installed a solid copper core, but I've done this for a while and never an issue. I will try the ignition coil first

The burn-away at the center contact of the dist. cap may be a clue.
Although there exists deliberate clearance between the rotor tip and the individual cylinder terminals in the cap (and hence an arc), the center, carbon, contact is spring loaded against the rotor. If the carbon or the spring were missing, or the spring were broken, the resulting arcs, in an area not designed for an arc, would quickly cause the observed damage.

As far as plugs I use Champion too.I used bosch,denso,NGKs bosch 3's and denso 5061's ,and they would carbon up in less than 6000 miles.Now running Champs for over a year.

Ismalley, check your Owner's Manual for the spark plugs specified for your engine. Modifying resistor spark plugs probably wouldn't be recommended by MB-trained techs. You are correct about the EZL. If it fails the engine will not run, and new/rebuilt ones are quite expensive. That's why you want to maintain the ignition system by-the-book. I take it you replaced the ignition wire from the coil to the distributor cap when you replaced the ignition wires even though it can be difficult.

Yes, I replace all wires with Bosch brand only. The spark plugs are correct, but finding non-resistor plugs for this model is nearly impossible so I use the oe plugs that are recommended and remove the resistor out of them and add in a solid piece of straight copper. I've not had an issue with this set up before, but just to be safe I'll go nab some more plugs without converting them and see what happens. It's only about $12 for 6 plugs so not an issue, plus if this doesn't help I'll just keep the plugs for my next tune up.

The extra resistance doesnt matter. But if it teally bothers you, you can switch to inductively suppressed wires, like magnecor, and eliminate the resistance in the cable rather than the plugs.

Why is the voltage regulator only lasting a year?

What ? Do you not understand how ignition systems work...or are supposed to work ?


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It's not lasting a year, I just replace it yearly just because it's free and it only takes me 5 mins. I do a lot of preventative maintenance on my car so a lot of parts that are common wear items rarely get worn down to the point of failure. Reason I do this is for peace of mind, I have the time to do it, and most of the replacements are free, I.e. Alternator/voltage regulator, spark plug wires, brakes, etc.

This made me open up my distrubutor cap today, it looks exactly the same the center pin is broken and is sort of melted. Contact points are also all corroded. Might have found my misfire at startup problem. Funny thing is I bought a new cap and rotor last year ??

The delicate center carbon contact is easily damaged when installing the cap due to the high ridge that it has to clear on the rotor. Cap must be forward enough to clear and then installed straight on. Room is very tight especially on the W201.

As far as the availability of none resistor plugs, I buy online NGK BP5EFS plugs for my M103 from one of the UK sellers. Price is excellent and shipping to Canada is very reasonable (unlike from the US) and I get them in about a week or even less.
I've been using these NGK plugs for about 10 years and I'm happy with them.

As far as replacing the alternator regulator and wires every year, unless you are doing 100k miles a year, it appears like an abuse of a lifetime warranty (no offense intended).

Depends on how you look at it. If I wait until the part fails it will be too late and most likely at the most inconvenient time, say Friday just after the parts store closes and probably somewhere away from home. :mad:

Got a pic?

The contact points on the edges of the cap get pitted, this is normal.

I can't place a diagnosis on the center pin without seeing it.

I kind of figured this was happening but wanted you to say it.

What is this, the "Minority Report" ? "These parts are being returned due to future failures".

You are committing "insurance" fraud, and making it more difficult for those with legitimate failed parts to be taken care of. Read the actual warranty and see if it states that returning good parts that you think might fail in the future is covered.

And, I'm betting some of your car problems are self induced by randomly changing parts.

I replace parts when they get towards the expected end of life not once a year for a part that should last a decade or more.

I also put about 25k miles a year on my car, which are not all highway miles, but that's besides the point. I've experienced having to pay for things during an unexpected breakdown or not having a vehicle because a part failed on a Friday night which left me without a car to get to work the following Monday and Tuesday. So I really don't think of it in terms of fraud. Especially when a voltage regulator goes out and I'm being told that it is "built into" the alternator and the entire unit must be replaced as a whole, while I'm holding the failed regulator in my hand. Anyways, I have had some self-induced issues with my car however I do not believe this is one of them.