What causes this?

[elt]

Doing a tune up on my 1999 gmc yukon. It had started misfiring badly. So new plugs wires cap and rotor. When i got to the rotor wow. I have never seen one this bad. Any thoughts?

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[915_Tahoe]

if that's the original cap i would just replace it, or you can try to clean up the contact. that should be normal to see for it's age.

gm#10452457
walk in price $17.48

 

[BG1988]

if that's the original cap i would just replace it, or you can try to clean up the contact. that should be normal to see for it's age.

gm#10452457
walk in price $17.48

i would not bother cleaning the contact is pretty much gone

 

[elt]

I replaced it and truck ia running good. I have never seen a contact burned up before. Was wondering if i have another issue that caused that.

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[BG1988]

I replaced it and truck ia running good. I have never seen a contact burned up before. Was wondering if i have another issue that caused that.

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normal wear how old is it

 

[iamdub]

+1 for normal wear. It's high voltage traveling through what is essentially a weak connection. Two surfaces constantly rubbing each other while millions of tiny electrical arcs peck it everywhere erodes the metal away. My guess is the average life of a cap and or rotor is about 60K miles, about 30K if you have an MSD box on it.

 

[alpinecrick]

How many miles on the cap and rotor? Was it an aftermarket or AC Delco/Delphi cap and rotor?

 

[elt]

I honestly do not know. I beleive it was ac delco but i dont know when it was installed.

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[drakon543]

the only thing i can add is distributor stuff on that engine you will want only ac delco. non ac delco stuff will not seal up well enough and allow excess condensation build up. typically noticed from a green splatter under the cap. excess moisture can cause extra arcing and burn it up worse than usual. anything else it seems to be hit or miss so spend the extra couple bucks for the good stuff.

 

[alpinecrick]

the only thing i can add is distributor stuff on that engine you will want only ac delco. non ac delco stuff will not seal up well enough and allow excess condensation build up. typically noticed from a green splatter under the cap. excess moisture can cause extra arcing and burn it up worse than usual. anything else it seems to be hit or miss so spend the extra couple bucks for the good stuff.

Yes. AC Delco or Delphi. The aftermarket caps leak........

Also, I suspect out-of-spec screws that come with the aftermarket caps contribute to the distributor base cracking around the screw holes.

And, AC Delco or Delphi on anything electrical or electronic such as sensors. Other manufacturers are a bit of a crapshoot.