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Distributer Knock/tap

B

boomer1

NAXJA Forum User
Location
Northglenn, Co
Just picked up a 1998 Cherokee sport - 4.0

Mileage 90,000, runs out really good.

I noticed what sounded like a valve tap, so I took the old fashion approach, with a long screw driver and tried to track down where the sound was coming from.

Wasn't coming from the valve cover, but is definately coming from the distributer cap.

Anyone heard of this one before, any ideas what might be causing it?

Thanks
 
What you have is the rotor button hitting one of the terminals in the cap. A little early in the mileage department though(mine went at least 150K +).

Easiest fix is a replacement dist,not cheapest way but most cost effective.

Wayne
 
OK? A "rotor button" hitting one of the terminals on the cap.

I guess I don't understand, is it the rotor, as it turns, hitting on one of the terminals?

If that's it, would replacing the cap and rotor help? Could they just be worn out. Would it be worth trying it?

If not, what is the distrubtor actually doing to cause the noise? It seems funny that it just started.

It sounds like replacing the distrubtor is the fix.

Will it eventually wear out and quit running or cause problems, or do I have some time?

Thanks
 
In my last post it was early and i was not full functional--now -its later--

What has happened is the shaft and the housing have worn to the point that the rotor is wobbling enough to make contact with one of the cap terminals,there is suppost to be a gap between them.
You may run this for a while until it throws a code and you have an engine misfire.

At some point it may let you sit.

Wayne
 
Any reason why it would wear out prematurely? I'm probably running the original distributor in mine (I don't recall seeing it on the service records when I bought the XJ with 171k) and it currently has just under 205k...no problems with the distributor.
 
there are 2 screws holding the dist. cap to the distributor, don't remove all the plug wires, so you don't get them in the wrong order. Inside you'll see the rotor button, pull straight up on it and it comes off. Look inside the dist. cap and looks for corrosion or impact marks on the terminals. Check the end of the rotor button for the same. If you need the rotor button it will cost you less than $10 at your local AZ or the like... dist. cap less than $15... can't hurt to see if it is the issue.
 
I've checked the rotor and the cap, both appear to be corroded. I think the first step is to replace both and see if that corrects the problem. If not, its off to pull and save to try and find a used distrubuter.

Thanks for the suggestions.
 
FYI

Thanks everyone for the suggestions.

As it turned out, a new rotor and new cap and the knock/tap is gone.

The rotor and cap were pretty bad, seems to solved the problem.

Thanks Again
 
boomer1 said:
Well the knock is back. I guess I'll have to replace the distributer.

Anyone else have this problem?

Thanks
Click to expand...

I did, my old dist. had alot of side to side play and vertical. Put a reman. cardone dist in and it went away. I also gained 1mpg according to the onboard computer lol.

Try pulling the cap and rotor off, then see if you can move the shaft around at all? if it has any side to side play then it should be bad. My new one has no side to side play at all.
 
Mine was running a little rough with 180k. Checked the rotor and it was destroyed. Hard to believe it was still running. Actually not bad after it warmed up. Replaced rotor and cap and it did it again. Checked side to side play and it was loose. Replaced distributer rotor cap and TDC sensor (inside distributer) and it runs a lot smoother.
 
Well the knock is back. I guess I'll have to replace the distributer.

Anyone else have this problem?

Thanks


What you have is the rotor button hitting one of the terminals in the cap. A little early in the mileage department though(mine went at least 150K +).

Easiest fix is a replacement dist,not cheapest way but most cost effective.

Wayne
Click to expand...
It was useless to try and only change cap and rotor, there is not many other possible cause than worn out bearing/bushing holding the rotor shaft.. It could have been something loose laying around but you checked right? That is why Wayne suggested to change the distributor right away.

Possible cause: cracked cap for a long enough time that humidity got in there and rust got followed..

Usually you should be able to SEE and FEEL it, playing with the shaft, or looking corroded around it, at the base (under the rotor)... Then again it's hard to diagnose over the internet.
 
grab ahold of the rotor with the cap off, side to side play is NOT ok. a little bit of in and out is normal but if it's got side to side movement the distributor is hosed. the tapping sound you hear is the end of the rotor smacking into the terminal tips inside the caps.
 
so i have side to side play. I've realized that i want to replace the distributor and my local dealership wants $550 for a new one. I'm slightly okay to do a new one but at that price i'm sure i could find something better...

Though upto now finding a new distributor has been a PIA. can anyone suggest one? $550 for mopar seems Insane
 
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