I have an 1989 D-150 with a 3.9 V-6. It has just turned 89,000 miles. It was running great until two days ago when I came out from work and started it and it had a noticable miss. I had done a basic tune-up about a month before; cap, rotor, plugs, filters, etc. and it's been running great since. I traced the problem to the #1 plug getting no spark (using a test lead/light borrowed from my neighbor who is a general automotive tech, works on all makes). I figured since the wires had a few years and miles on them (probably 35-40k) I thought I had a bad wire & replaced the wire set, Still had the same problem. I checked wire resistances, swapped wires, swapped plugs and even changed the cap & rotor to be sure I had the problem traced and covered well. All other plugs seem to be firing & burning well except that one. On closer inspection of the old cap, I noticed what appeared to be light gouging in a few of the contact points, the worst of which was to the #1 plug. I spoke with another friend who is a Dodge dealer tech & he said he thought I had worn bearings in the distributor that was causing that problem. Has anyone else run into this? Don't want to run out and buy a distributor unless this is most likely the issue. Can't think of anything else that would cause no spark to only one plug. Any help would be greatly appreciated. Thx. John.

 

After changing all the ignition you have retested that wire for spark?
Best way is to remove plug wire from plug, insert phillips screwdriver into wire and with friend cranking over truck see if spark will jump 1/4" to exhuast manifold or other close ground point. A slightlu easier way is with a spark gap tester from the auto parts store..NOT the neon light tester. You want what looks like a spark plug with no side electrode and a clip soldered on the case. That gives about a 1/2" of gap and if that fails then check spark at the coil wire, if taht fails also then replace coil, retest.

Buck

 

Yep, retested that wire several times. No matter what I did, it was always the same one. FYI, the tester I used was specifically a spark tester, I think from Snap-On, but I also did it the old-school way first of using a screwdriver in the wire to a ground. There was nothing on that plug wire, and PLENTY of zing on the rest! Got good spark jumps from all five other ones, including a bite or two when I got too close and grounded myself! LOL! Comes with the territory. Will try testing with an extra coil I have for my 76 Dodge van, which should be close enough to the one on the truck, for testing purposes anyway. I guess why I was passing over the coil before was that the rest of the plugs seemed to be firing good.

Thanks for the help & good tips.

John


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Any chance you stuck on a wrong cap? It really doesn't make sense that you have good spark on all but one with a known good wire.... I guess a reluctor tooth could be bad, but that sure is rare. Reluctor is the toothed wheel under the rotor.

 

Now you sound like me! I have been scratching my head over this one all weekend! I'm no expert, but I've been working on cars since I was 14 & it really doesn't make sense . . .

Anyway, to answer your question, I had done the initial tune-up about 6 weeks prior to the problem surfacing, and the truck ran great until the one day I came out of work and started it and it was missing. At first, I did an armchair diagnosis and figured that since it had been at least five years since I last changed wires, they could be due. It just made sense, because like I said, the truck just had a tune-up and was running good before this. I also bought a new cap & rotor the day I changed the wires, replaced those and still had the same issue. I doubt I got two incorrect or bad caps. I double-checked the wires to be sure I didn't screw up the firing order, and they are correct, not that that would affect spark. The story I got from the Mopar tech was that if the distributor shaft was wobbling, it would affect how the reluctor worked.

Buck, I appreciate the feedback. I'm trying another coil tonight after work, then a replacement distributor if that doesn't pan out. I'll post the results! If you have any other ideas, let me know. Thanks again.

John

 

Got it! The problem was the distributor. I checked coils first, and found that both a known good coil and the one in the truck measured about 6 ohms. I installed the good coil anyway and nothing changed. Then I yanked the old distributor and spun the shaft. It wasn't wobbling, but there sure was something loose inside. I looked through the holes in the black plastic cover under the rotor and found that the plates inside had apparently separated. That must have been going on for awhile, because I thought I had fuel injection issues too, since I was getting a strange hesitation once in awhile when I put my foot into it . . . almost like when an accelerator pump goes bad in a carbureted engine. Once I installed the new distributor & put my original coil back on, it fired right up and ran like new. Much better now. No hesitation. Hope this helps someone else out there. Thanks to Buck & the Dodge Forum!

 

yep your distributor shaft was moving due to the plate seperation, prolly why your friend thought it was the bearing. It was cause the rotor to get to close to your #1 piston contact in the cap." gouging on that contact" and it didnt have correct air gap. Glad you got the prob fixed tho, congrats

 

Glad its fixed and definitely a one for the "uncommon" folder..I owned a 92 Dakota with the V6, had the worn out distibutor bushings but never caused a no spark on 1 cylinder issue!

Buck