Engine skip in damp/foggy weather

[markqc]

Hi All,

1996 4.3L 5spd Chev. P/U

Whenever it is foggy (or sometimes wet) I notice the engine will "skip a beat" every so often when running around 1800 to 2500 RPM. This usually will be noticeable during acceleration or just at cruising. The plugs are about a year old (AC Delco), the cables are new (Bosch, Got tired of buying GM parts) and the cap and rotor are about 6 months old (AC Delco) If I change the cap & rotor again I am sure it will fix the problem as it has in the past, but they don't seem to last very long. The cap has some oxidation on the terminals (under the cap)
Anyone else experience their cap and rotor not lasting very long or an engine skip in damp weather? Any ideas?

Thanks,
Mark

[corning_d3]

It does sound like a bad cap/rotor, or possibly a defective coil. What brand of caps/rotors are you buying?

[MyTOY]

I've read there is problems with the vent screens clogging
on the bottom of the dist. housing and gases & arcing fouling the cap.
GM has new part #'s with larger screens. You can blow
them out with air. Also PVC issues can cause probs.
Something to think about.

[markqc]

Thanks for your replies. The cap and rotor have always been AC Delco, but next time I may buy a different brand. Any recommendations? They seem to be lasting less than a year now (which is about 20 to 24KM)

Where is the "vent screen" located? How would I go about blowing the screen out? Do you think this could cause the terminals under the cap to oxidize? Do you think I would be able to use some 600 grit paper to clean the terminals and replace the old cap?

I don't recall changing the PCV valve. Do you think this could cause the engine to skip in foggy weather but not in dry weather?

Thanks,
Mark

[corning_d3]

You could clean the terminals in the cap tower, but that would change the air gap and possibly make a mifire condition worse. I see nothing wrong with AC Delco parts, I use and recommend them. I'm beginning to wonder if this isn't being caused by something else. Have you tried swapping the coil with a known good one?

[markqc]

I agree with your opinion on the AC Delco parts except that they are a little pricey. I have always used only AC Delco, except for the wires I just replaced. The coil was last changed about 4 years ago. I agree that something must be causing the terminals to corrode and break down, but what? Could moisture be getting in or not being able to get out somehow?
I'd like to hear more about this "vent screen"

Thanks,
Mark

[MyTOY]

The vent screens are in the 2 tubes sticking out of bottom. I've read
a tech bulletin saying to blow out with air but I haven't done it. It
also said the clog with cause gases & arcing to leave white or tan
deposits & encrusted. I don't know about the damp day probs.
The article stated the caps are prone to failure because:
- the venting prob
- condensation dripping from a/c accumulator line right above
- low profile design
- the manufacturing challenge of the close proximity of the terminals
- oil ascending up the dist. shaft
- improperly magnetized dist. shaft at factory

[markqc]

MyTOY,

What you describe regarding the white/tan deposits is what I am seeing. Can you send me a link to the service bulletin?

(The cap seems to get the deposits within 6-10 months now, so hopefully the screen is the easy fix. I think the damp weather just adds to the problem)

Thanks,
Mark

[MyTOY]

http://www.mightyautoparts.com/libra..._techtips.html
it's the "pattern failures" topic

[markqc]

MY TOY,

Thanks for the link. This looks like my exact problem. I will have to try to clean the vents and perhaps change the PCV valvle before replacing the cap & rotor again. Hopefully I can do this without having to remove the distributor.

Mark

[markqc]

The vent holes are visible when the cap and rotor are removed. I blew compressed air through them and could feel the air coming out the underside. I also used 600 grit emery cloth to remove the white deposit on the cap terminals and the engine now runs better in the damp/foggy weather. Now I'll have to wait and see how soon it acts up again.

Thanks for the help,
Mark

[markqc]

The engine skip has returned with the damp/foggy weather lately in the Toronto area. This time I replaced the cap & rotor with "champion" instead of GM parts. Funny enough, the champion box had some literature discussing the corrosion & venting problems, and going so far as listing two GM service buletin numbers. No surprise that the GM parts do not come with this literature. It did mention to remove the vent screens if so equipped (my 1996 does not have them) and to check the PCV valve (seemed good to me). Hopefully all the air I blew through the vent holes and the new cap & rotor will make the difference.

Anyone else experience this problem of the cap only lasting 6 months due to corrosion on the terminals? When the truck was newer a cap would last at least 3 years. Any other ideas how/why the moisture can affect the cap?

Thanks,
Mark

[primal1]

i'm having the problem that moisture is collecting inside the cap and crerating misfires. it happens about every 6 months.