'94...won't start in wet weather

My 94 Roadmaster has a big time problem almost anytime that it rains. I'm sure it's a sensor somewhere, but after it dries out, my mechanic can't tell which sensor (if that's the case at all) is acting up. I'm not talking running through water puddles, I'm just talking sitting in the driveway for a fer hours while it is raining. Anyone else ever have this problem ??? Any suggestions ??

You might want to check the distributor cap. You didn't say exactly what the problem is, but I had a VW for a few years that had a similar issue. For some reason the dist cap kept developing cracks an this would allow enough moisture into the cap to cause problems. Everytime we replaced the cap it would be fine for a while and then it would come back. I don't know that this is your issue, but it's something to look in to. Let us know what you find. M

.... absolutely correct. I have been "surfing" all day, and that seems to be the consensus. I had my distributor replaced (at considerable cost) a few months ago, thinking that was the problem. Alas, the condition continues. It looks like I may have put on a new distributor and fixed nothing. Assuming that moisture is the culprit...... does anyone have any suggestions on how I could go about sealing this thing, or keeping it from getting wet..... or should I just go back to my mechanic and get him to put in a new gasket or something??

Well what cap kit did he install on the opti? Most likely it was no an AC delco part, so the seal could have been bad. Opti sounds to be your problem.

You're best bet would be to go and buy a whole new optispark from GM. Through a well known parts guy ( i can give you his #) a new optispark is around $240 shipped including a new vent harness and it comes with a two year warranty.

Engine Miss/Poor Driveability Symptoms #87-65-27 - (Feb 18, 1999)

Engine Miss/Poor Driveability Symptoms (Install Opti-Spark (ABITS) Distributor Assembly Service Kit) 1994-96 Buick Roadmaster
1994-96 Cadillac Fleetwood
1992-96 Chevrolet Corvette
1993-97 Chevrolet Camaro
1994-96 Chevrolet Caprice
1993-97 Pontiac Firebird/Trans Am
with 4.3L or 5.7L Engines (VINs W, P, 5 -- RPOs L99, LT1, LT4)
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=583354&pubid=-1&evc=sm#ss1-583354">Condition

Some vehicles with the above engines and equipped with the Opti-Spark (ABITS) ignition system may exhibit an engine miss and/or poor driveability symptoms.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=583354&pubid=-1&evc=sm#ss2-583354">Cause

The (ABITS) cap and the rotor may show carbon tracking, cracking, or water intrusion which can cause an engine miss and/or poor driveability symptoms.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=583354&pubid=-1&evc=sm#ss3-583354">Correction

Perform strategy-based diagnosis. If it is determined that the ABITS cap and/or rotor is the source of the concern, then a service kit may be now implemented instead of a complete ABITS assembly.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=583354&pubid=-1&evc=sm#ss4-583354">Parts Information

There are two (2) variations of Opti-Spark Distributors. It will be mandatory to identify which type is to be serviced for proper parts procurement.

The Opti-Spark Distributor II (Pin Drive -- WITH positive vent system) can be identified by the intake manifold vacuum hose connection (3), the air intake duct hose connection (4), or the non-splined pin drive (1). Refer to Figure 1.
The Opti-Spark Distributor I (Splined Drive -- WITHOUT positive vent system) can be identified by the splined pin drive (1) or the lack of an intake air vacuum hose connection and an air intake duct hose connection. Refer to Figure 2.Distributor
P/N
Application
Kit Contents
Opti-Spark I (Spline Drive) (No Vent)
10457735
92-94 Y
93-94 F
Distributor cap, rotor, screws, and washers
Opti-Spark II (Pin Drive) (Positive Vent)
10457293
94-96 B,D
95-96 Y
95-97 F
Distributor cap, rotor, cover, screws and washers

Important

It is necessary to use tool J 39997 (or the equivalent) for the distributor cap screws and tool J 39998 (or the equivalent