'84 Carrera stumbles when wet

[Mex]

This is essentially a continuation of and earlier thread (link below), but is sufficiently different to warrant it's own.

Sputtering, Bucking, Sneezing(!?) 3.2

In any case, I've replaced the DME relay, flywheel and CHT sensors, fuel filter, air filter, and breather hoses (they all needed replacing anyhow), but I'm still experiencing a significant stumble. However, I've only noticed it happen while driving in the rain or when damp.

I've been reading old posts and the distributor cap seems like a common culprit, but it seems to usually causes a no-start situation. My car starts fine, but develops the stumble a few minutes into the drive.

Any suggestions besides the distributor? Am I safe in assuming it's either a vacuum leak or electrical problem? Thanks

[Hugh R]

Plug wires, open the deck lid at night, run it and have a spray bottle of water, look for a light show.

[Bob Kontak]

Originally Posted by Hugh R

Plug wires, open the deck lid at night, run it and have a spray bottle of water, look for a light show.

+1

Give your eyes time to adjust - 5 minutes minimum - then be marveled by your electrical integrity shortcomings.

[Mex]

Originally Posted by Bob Kontak

electrical integrity shortcomings.

Hah, gonna have to find a way to work that into a conversation with my electrical engineering friends.

Thanks, I'll give them a spritz and see what happens.

[SpyderMike]

Mine took a while to diagnose...but I had a slight gap in the spark plug wire boot end at the distributor cap. Moisture would travel down the wire into the gap at the spark plug boot and short out that plug wire. A little red RTV around each wire as it enters the spark plug boot fixed it for good.

[Mex]

Ok, quick followup question. I noticed my distributor cap looks different from the one pelican lists in the catalog for a 3.2 (crappy phone pic below). It looks more like the style used in the SC. Does this really matter or should I replace it?



Also, I noticed a split sheath on a bundle of wires running left to right from the driver side edge of the engine bay near the headlight relays. Are they ignition related/would they contribute to the problem I'm having?

[SpyderMike]

Rule this out...put red RTV in the boot joints especially on the wires where this joint faces upward (right hand side of photo). On damp mornings, the moisture was traveling down the wire and shorting out my plug wires. I put a small amount of RTV around these locations and cured my stumble during damp/wet. It is simple and cheap and will rule this out. Just a thought.

[Mex]

Originally Posted by SpyderMike

Rule this out...put red RTV in the boot joints especially on the wires where this joint faces upward (right hand side of photo). On damp mornings, the moisture was traveling down the wire and shorting out my plug wires. I put a small amount of RTV around these locations and cured my stumble during damp/wet. It is simple and cheap and will rule this out. Just a thought.

Ok, I'll be sure to do that, thanks. Any idea what those wires in the other picture go to?

[KTL]

There's no headlight relays in the engine bay. That separation you see in the picture is no big deal if no damage to the wires. You can remove that harness by disconnecting it behind the fuse panel. It is a large rectangular plug that is intended to be unplugged. That bundle of wires however is very important. It's the main wiring harness connection from the chassis to the engine.

You have the correct distributor cap. No worries there. But it could need replacement. A cracked distributor cap can allow water in and short the electrical contact. I would start with the plug wires like the rest of the guys said. Plug wires can give you problems in a lot of ways:

-spark plug connector on engine can get pinholes in the insulator and allows the spark to short to the cylinder head
-spark plug connector has resistors in it that can go bad.
-water entry into boot like SpyderMike said
-damaged/aged wire insulation that allows loss of spark

The distributor cap is very easy to remove. Long flatblade screwdriver is all you need to push down and turn the spring-loaded screws free from their hook points on the distributor housing. Look under/inside the cap when you release it, and also check the rotor tip for carbon tracking and damage to the metal tip.

[Quicksilver]

I wouldn't glue the boots on with RTV. Why would you want a permanent gloppy mess?

Dielectric grease. Use it.
- Seal the boots to the spark plugs and the distributor cap.
- Seal the boots to the wires.
- In really bad cases do a partial seal of the cap to the distributor.

You can tell you have a great seal when you push the boots on and they try to pop right back off from the trapped air. On the distributor cap I will pinch the side of the boots to 'burp' them. On the plugs that is not possible. Luckily the plugs operate over the boiling temp of water so it isn't a big deal.
When sealing the wires to the plug you want to pull a bit of the wire out of the boot, lube it with dielectric grease and then push it back in. That will create a complete seal.

If you have good plugs, quality wires, a good cap, and follow these procedures it is damn near impossible to have an issue.

[Mex]

RTV on the wires and dialectric grease on the connections seems to have done the trick. It'd been dry in upstate NY since I did the fix (go figure), but today we got quite a drenching and she didn't stumble once. Thanks a lot for all the help, I can always count on a Pelican

Now on to the oil leaks...