'98 C1500 4.3 Ignition question

C-ya

Original poster
Member
Aug 24, 2012
1,098
Hey gang, my question is on a '98 C1500 4.3 with an external coil. I bought it used in '04 with 140K on it and sold it with over 240K. Drove great, ran fine, no issues. One night I was driving home from work and ran through some deep(er than I thought) water over the road in a low lying area during a heavy rain. It started running rough, missing, almost wanting to die, but it would stay running, but with very little power. Next day, started and drove fine so I didn't think any more about it. Then, after a drill weekend, I was getting ready to leave on Sunday afternoon. Rained all weekend and was still raining. Get in, try to start and it just cranked and cranked. Finally caught and ran, albeit rough. I thought I was going to kill the battery or smoke the starter and/or wires. Made it home, coughing and chugging. Next morning, dry, started right up and off to work I went. Next rainy weather we had, it would not start. Drove the wife's car to work and had it towed to a local garage for diagnosis. Weak spark. Their fix was to put in a new coil. Since I know a whatsit from thingamajig, I said I'll do that. $50 for their diagnostic fee. Not terrible. I go pick it up and drive to Auto Zone and get a coil and head home. Thirty minutes later, I have a new coil installed. Next rainy weather, no issues. Fast forward a few months to the next humid time and here we go again. I immediately head to AZ and get a new coil, this time about 20 minutes later and the new coil is in. Fires right up. Process repeats a couple more times before I sell it to a guy here at work last year when I got my TB. We changed the coil shortly after he bought it, and it did the same thing the other day when it was rainy and humid.

My question is why this would keep repeating? Is there a wiring issue that could cause this? Should dielectric grease be used somewhere? Anyone else ever see this on a GM platform? I have been around GM's my entire adult life (and even worked at a garage for a couple of years and saw all kinds of fun problems) but I have never seen a repetitive fault like this.

Thanks!
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
I would have first suspected bad wires, cracked or old distributor cap and rotor and then I would have went to the coil. Dielectric grease in the boots is also good.
 

C-ya

Original poster
Member
Aug 24, 2012
1,098
I neglected to mention in the first post that I had just done a tune-up on the truck and after that happened, I replaced everything again just to rule out those items.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Hmmmm. Not much left. Maybe the pickup coil in the distributor? Distributor cap sealed properly? Do you have the ignition wires to the spark perfectly lined up to one another? You should cross them over each other at least once to prevent inductive cross-firing. When it's acting up, you could run the engine in total darkness and look for any arcing along the wires.
 

C-ya

Original poster
Member
Aug 24, 2012
1,098
OK, say it is the pickup in the dizzy. How do you fix it? You can't seal the dizzy any more than making sure it fits correctly, right? I think the distributor itself has a vent hole in the bottom of it. Maybe not this particular model - not sure. I seem to remember one when I was building the SBC for my Hombre and I used an HEI dizzy with the coil in the dizzy.

If it was cross-firing, wouldn't that happen at all times? The only time this issue rears it head is when it is very humid and the coil is getting close to 8 months to a year old.

Would moisture in a crank position sensor plug contribute to this? May have to tell him to look there. It is a hard start, rough run when it does start, so I'm not sure if the CPS is involved or not.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Once it's fully warmed up and the moisture dries, it should clear up. I was just throwing the pickup coil out there as a possible place to look. It should be replaceable. On my S10 Blazer with the same engine, the screw hole was stripped in the dizzy and didn't hold the cap tight so I had to go to a slightly larger screw. If I remember correctly, there is a vent on the top of the cap. Maybe try spraying WD40 inside.

My mum in law had a Corsica with a 2.4L that was always hard to start when it was raining. Changed everything, coils, wires, plugs, sensors, nothing worked. Wound up scrapping it!
 

C-ya

Original poster
Member
Aug 24, 2012
1,098
That's the problem - it doesn't clear up until humidity goes down or you put a brand new coil in.

Thanks for tossing ideas back and forth with me. I was hoping someone would come along and say, "Put this right there" and it would be fine. Wishful thinking, I know...
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Oh well, gave a good try. Good luck.
 

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