Misfiring / cross firing

[portajon]

Ok... I think I found the right place to post up this issue.

After owning and servicing four of these vans over the years, I thought I had seen it all. That's why I bought a nice '96 model with 25K on a crate motor. Good body, interior great, little old lady just drove it to church and back.... never even listened to the radio, you know.

Anyway, van has an issue with misfiring. First action was to check secondary ignition. Right away, I noticed that the D cap contacts were in bad shape. New cap and rotor installed. Presto.... van runs like new. For about 500 - 1,000 miles. Then it gradually begins to misfire, first at highway speed, then worsens until it is misfiring going out the drive. Order a new cap and button.... presto... runs like new.

So, after the third cap was burned up, I decided I should try a higher quality, brass contact contact, instead of aluminum. I thought maybe it was just cheap aluminum contact caps and surely a quality brass contact cap would give better service. Not at all. Same results.

Now, what I can see is that the contacts are being burned at an odd angle. The fire is coming off the rotor "late" so to speak. All of the spark contact is coming on the side of the contacts, rather than center. So.... my noodle tells me something is off here with timing.... just a hair. Causing a longer, hotter spark that is burning up the contacts on the cap.

My next move, I THINK, is to replace the distributor. Shaft or pin or gear wear? Something causing it to be off? OR... is this sensor related? Cam sensor?

Any ideas for me?

Thanks for any help if you have seen this before.

[Kidhauler]

Try new leads as well if the resistance is too high from bad leads it can cause all sorts of weird problems. Have you checked the timing with a gun? If you can't adjust the timing enough it is possible that the Dist was put in one tooth out of place.

[portajon]

Thanks for the reply.

Not familiar with any timing adjustment on a '96 Astro. Far as I know, the timing is set and advanced by the ECM according to sensor input. The distributors on these vans are locked down in one position.

I have heard of the "one tooth" idea before and have placed the distributor both one tooth back and one tooth ahead, and the engine won't run. What we have here is a very, very small something, because the van runs really well otherwise... it runs perfect with a new cap.

I have also considered that I may try new wires, for the reason you said.... perhaps high resistance is an issue BUT.... that would not be cured with a new cap, if the wires were the issue, the problem would persist, regardless of the cap. The progression here is that for some reason, the contacts inside the cap are being burned very quickly. THAT is where the resistance is coming in. Once the contact is burned and damaged, you start getting cross fire to other points inside the cap. I even vented one of the caps to see if condensation or engine vapors were causing the issue. Didn't seem to help.

I am still leaning toward something being wrong with the distributor itself.... shaft, bushing, gear?

[Stroverlander]

I was going to ask about distributor gear wear but seems like you would have noticed it already.

It's hard not to try a new distributor when you can get a WPS DST1639 for$50-$60 or United 9363 for under a $100 from Rock Auto/Amazon/Ebay. Both seem to be pretty solid.

[portajon]

Thanks for the reccomendations on distributors. I am always wary of aftermarket parts for critical areas of perfromance. Those 3,000 mile fuel pumps will sure teach you a lesson about that.

I haven't noticed any play or gear wear at this point, but I haven't specifically looked for wear or play either.... it just occured to me as I was trying to apply logic to what the heck this could be.... I will definitely check for wear and shaft play next time I pull the dog house... which will likely be when I am replacing the dist. anyway.... unless someone comes up with a sure - cure secret outside of that.

What about a salvage dist.? Prolly risking getting a worn out part there.....

[Stroverlander]

I'm also wary of parts like that and prefer OE or better for the most part but fwiw, I haven't heard of anyone having a negative experience with either of those two distributors and the aluminum housing is a plus compared to the stock plastic that can/will crack.

[WoodButcher]

My '97 is the same way jon.
A few years back I bought a dizzy from Skip White Performance, came w/ accel cap and rotor IIRC. That got me 2 years and then it became a yearly ritual or less again. (depends on the quality of the cap) I hogged out the hold down clamp for the dizzy in an oblong shape and that allowed me a couple degrees of mechanical timing adjustment. It helped a little but I still have a yearly date with a dizzy.

If you find an answer please post it. While my '97 can't have much left in her 280,000 miles currently I'll keep feeding her caps until she can't swallow.

[portajon]

Well... at least I'm not the only one experiencing this.

It's a very weird thing. I went and helped a buddy yesterday where a tree had fallen across the back of a house he uses for storage. We cut it up and used the van to pull some large sections of that oak tree away from the house and out to his back lot. Now.... the van had reached the late stages of the new cap - to - misfiring cycle and I have been thinking about what to do next about it (hence my post here).... but after putting the engine under a bit of strain pulling those logs, it completely stopped misfiring yesterday afternoon on the drive home.

It's a real head scratcher. If I learn anything I'll be sure to post up.

[Smiliesafari]

I just went through a similiar situation. The coil was in self destruct mode until it finally quit. New coil fixed it.

[portajon]

OK... pretty sure it is a bad distributor. Found this guy with an explanation:

https://www.youtube.com/watch?v=se63j2q_5GA

I pulled the dog house this morning and checked for loose play and there is a ton of play in the distributor, up and down. This allows the shaft to move up and down, thus allowing the rotor to swing through several degrees. This explains the evidence I found of the spark coming on the sides of the cap contacts rather than centered and also explains why this misfire changes when the engine is under power. Depending on engine speed the gear moves up and down, advancing and retarding the timing at random.

Pretty sure this is what is going on. Ordering a new distributor. Will let yall know how it goes.

[portajon]

Ok, so yesterday I needed to drive into Rock Hill anyway, so I went by the U Pull It yard and grabbed a distributor out of a Jimmy. $11 and change. Installed it last night. Van is running like a champ. The cap on the used distributor was in good shape and had a manufacture date stamped on it of 6/13. So I left that cap on there. Will keep posted on if and when there is any progression back into the misfiring. But for now.... happy van, happy man.

[Longhair]

I just went through the same thing. Darned plastic distributor!

A guy I know with a repair shop said that in order to time it perfectly he would put his Modis scanner on it (a timing light doesn't work right). Regardless of which tooth used the replacement distributor wouldn't get any closer than 17° (needs to be set at zero). We ground some out of the insides of the clamp to give us a little adjustment and got it dead on.

[portajon]

Update:

Over 60 days since installing the salvage distributor and it hasn't skipped once. Thrust washer, gear wear.... crappy plastic housing? What ever the booger is that causes this is in the distributor.