What Causes Distributor Cap Deterioration?

"Intriceight" wrote: ('02 Durango R/T 5.9 56k mi.)

Truck would crank but not start. Distributor cap was in bad shape, with the center rotor button looking like it had been partly burned off, and some arcing on all the other contacts. A replacement cap and rotor only lasted 30 miles before the same thing happened, burned rotor button. A third cap and rotor have lasted 60 miles so far but it feels like it's starting to do the same thing because it's taking a little longer to start up than when I first changed it, and there's a slight shudder in the engine. What could cause the distributor cap rotor button to be eaten like that? ___________________________________________________

Ignition coil voltage rises until the air gap in the plug is ionized enough to conduct. If plug gaps are extra large, or if plug/coil wires have breaks, or if the plug/coil wires are not fully inserted, the resulting higher voltage spikes will put extra stress on all secondary (high voltage) ignition parts.

The cap's button shouldn't see much spark because the rotor contact is supposed to touch it continuously, but you might look for an excessive gap somewhere in the system. Because it happens so quickly, I would suspect the coil wire first.

Other possibilities:

Cap & rotor materials are substandard. Rotor is not fully seated, extra force wears out button. Rotor contact is not touching button, gets sparks.

Good luck.

Rodan.

Rodan, Thanks for the info. That makes sense to me. I had replaced the plugs, making sure of the correct gap, but did not replace the wires because they are only about a year/15,000 miles old.

If the wires are fine, could the coil itself be the problem, maybe sending too much voltage?

What about the crankshaft position sensor? I've heard/read about a lot of problems associated with that sensor and starting problems, but I'm not sure if it would directly affect the distributor cap.

Thanks again for the help. J

Add lean air fuel mixture to his list... Cheapy cheap AutoZoo wires will usually only last a year or 15K miles, better wires such as Echlin, Prestolite or Standard Ignition last much longer. If you mishandled the wires when you removed them to change the spark plugs, you may have stretched and broken the conductive core inside the ignition cable, increasing resistance and driving coil output voltage sky high.

The coil outputs voltage in relation to the circuit resistance, more resistance gets you more voltage, less resistance gets less voltage. The coil can't output too much voltage in and of itself.

Nope, highly unlikely.

What color were the old plugs?

How could it? What possible difference to the secondary could firing at

10 degrees BTDC vs. 5 degrees ATDC make? It's firing at at the same frequency, same dwell, just at a different point along the cycle.

Firing at the wrong spot in the cycle will cause all kinds of running problems, but it won't cause any different wear in the secondary.

aarcuda, I have Autolite wires on now. I did have a cheap cap and rotor when the problem started (GP Sorensen), and I replaced it with the same cap and rotor at first, but when that cap died after 30 miles, I figured I'd try something better and bought Echlin. Now I've got 70-80 miles on this cap and rotor, and while I haven't had a non-starting issue, the truck is stuttering slightly at an idle, and it doesn't have as much power as it should. When I first replaced the cap and rotor, the truck ran very smooth and had all kinds of power, so do you still think wires could be a problem?

The plugs I had in it when all this started were Bosch Platinums (I know, I read all the bad things about these plugs too late) and when I took them out, they were all pretty bad, 3 or 4 of them were fouled out. I don't know if they fouled out because of all the cranking I was doing on the engine trying to get it to start, or if because somebody who I had look at the truck to try and figure out my problem switched the wires on 4 of the plugs, then started the truck up.

Now I have Autolite plugs, properly gapped.

Thanks, J

How do the wires look? I'd more suspect the coil. How does the spark look if you pull a wire and hold it near a ground?

Does the ECU have anything to report? Suttering could be a *lot* of things including the fuel system and may be a problem totally separate from your initial starting problem.

Yes, I still think the wires could be the problem. I'm not a big fan of Autolite wires and their spark plugs would be my third choice behind NGKs and Champions.

Some time spent with an ohm meter may reveal whether they're bad.

It's arcing, because it's not making good contact.

This can be caused by using poor quality parts that don't have quite correct dimensions; with my old Chrysler I found that I had to use the cap and rotor from the dealer and none of the third-party parts would work. I've had plenty of other cars that were fine with third-party ones, though. But that one model had trouble.

It can also be caused by the shaft having too much play in it. When you change the rotor next time, put your hand around the shaft and see if you can move it up and down a bit. If there is any play there, it may be time to replace the distributor bearings.

--scott

The wires appear okay, I don't know anything about an ohm meter (I don't know much about electrical, or vehicles in general), so I'd probably just do trial and error and buy new wires. I'm at work now and can't check the spark until tonight, but what should it look like? I'm thinking the fuel system should be okay considering how great the truck ran when I first replaced the cap, rotor and plugs, maybe I'm wrong though.

That sounds kinda like something that could be caused by a leaky or open condenser (capacitor) from the old days. What part provides that damping function now?

Running with atrocious timing could do that too, couldn't it? What does OBD II have to say about this (well, probably a number of fault codes, if the truck is running so pukey, but there might be something about timing or the engine computer in the mix).

Giving the problem a fair chance to be easy: Sure all the connectors are connected solidly? Everything that should be grounded, is, and everything that shouldn't be, isn't? Inside and outside of the cap are clean?

Just some thoughts,

--Joe

Yeah, I triple checked everything is clean and grounded. I guess I'm just going to replace everything, and if I'm still having problems, then I can look away from ignition and focus on something else.

I like oem for ignition parts. I think that you save money, because they outlast aftermarket. Lack of problems such as you are having is a bonus.

If you're chewing up distributor caps with electrical arcing between rotor and plug-wire contact in a few tens of miles (they should be good for several thousand miles and acceptable through a few tens of thousands) , you definitely have an ignition problem (though there might be other problems too). Something on the secondary (high voltage) side is on the fritz bigtime.

Anyway, a followup to another poster made me think timing per se might not be a contributing factor, but rather badly off dwell, or whatever the computer equivalent of dwell might be. A sensor problem is one thing to look at, though I suggest doing this methodically rather than just throwing parts at it -- reading-out the On-Board Diagnostics II trouble codes and seeing what it tells you might be a good first step.

I am thinking that the plug wires are not a problem after 1 year/

15,000 miles of service. They should be good for a few years... unless you did something systematically bad to most or all of them, physically, when pulling them off the old plugs and putting them on the new. Some of today's wires with carbon innards have to be teased off gently, and are pretty easy to mess up if you pull too hard before they're ready to leggo... been there, done (and fixed) that!

--Joe

I'm going to ASSume that the car in question is the 02 5.9 Durango in your sig.

On the 5.2 and 5.9 Magnum engines, the distributor housing position doesn't change the timing (that's set by the crank positioin sensor). But if the housing is incorrectly rotated, such as after a distributor swap, the rotor will be pointing away from the correct "tower" on the cap, causing an excessively long arc inside the cap, which will definitely chew things up rapidly. Check the phasing of the distributor to make sure that when the engine is parked at TDC on cylinder #1, the rotor is pointing DIRECTLY at the #1 cylinder wire.

Thank you everyone for you help. I changed the coil, cap and rotor today. I learned how (kinda) to use an ohm meter. The original coil was at 18 (or 19,000, I'm not positive how to read it) and the new coil was at 12. I figured that was way too much resistance for the original coil so I replaced it. The wires ranged from about 7 to 9, I compared them to new wires that I bought from NAPA, and those ranged from 5 to 7 (depending on the length). I decided not to change the wires because that didn't seem like too big of deal to me and I would like to keep the $50 they cost. The cap and rotor are OEM Mopar, so hopefully I'll be okay there.

Once I get my brake problem fixed (sticking calipers) I'll do some driving and let you know how all the ignition repairs went.

Thanks again, J

It's been a few weeks now and I haven't had any problems other than the gas mileage is a little low. I'm going to run some cleaner through the system. Thanks.