Chronic ignition problems with 1996 Suburban, replacing distributor cap makes it go away

Question

I'm trying to diagnose an ongoing ignition problem with a 1996 Chevy Suburban. Sometimes it won't start, and the previous owner said this happens regularly, and every time the problem occurred, replacing the distributor cap made it work again. Obviously replacing the distributor cap again and again is not a reasonable solution in terms of cost or inconvenience, and it's obvious that there's some other underlying problem that's either ruining distributor caps in a hurry, or (more likely, in my opinion), which is going away for a while just as a result of doing work in that area, most likely moisture- or grounding-related.

Unfortunately I have not seen any of the caps that were replaced, so I can't comment on their condition, however I did find this:

http://www.handymanlyness.com/archives/auto/repair/ignition/distributor_cap/GM_truck_1/replace_cap_96_Yukon.html

which mentions:

With another truck, I've had problems with a coolant leak letting traces of anti-freeze into the distributor cap and causing the exact same problem this truck had... difficulty starting in damp weather with a cold engine. The anti-freeze would absorb moisture from the air and turn into tiny droplets of conductive liquid, which would ground out the spark and prevent the vehicle from starting. I could solve the problem by heating the cap with a heat gun or hair dryer, and the truck would start just fine.

Unfortunately, nothing is said about where the coolant leak was coming from, and I'm a bit surprised that coolant would be leaking into the distributor, which is situated on top of the rear part of the (V8) engine. Does this explanation make sense at all? If so, where could the leak be coming from?

I didn't check (and I'm not near the vehicle now) whether it's using Dexcool, but based on the year, it might be. I've also heard reports that Dexcool has, or deteriorates to a form that has, higher conductivity than proper antifreeze, so if there is a very slight leak causing the ignition problem, is there a chance replacing the coolant might fix it, and can this be done safely in a vehicle made for Dexcool?

Update: Here are some other threads with a similar issue:

http://townhall-talk.edmunds.com/direct/view/.f14f5d1/141

Also, I should mention that if the issue is moisture related, it's almost certainly not ambient moisture, since the vehicle started yesterday after a long time of sitting (it hadn't been working before) with overcast weather (previously heavy rain) and near 100% humidity.

Answer 1

Something which might help you diagnose the issue better is to do an old school trick on your just replaced distributor cap. This would be to generously spray the inside of the cap and the rotor with WD-40. Many people use this as a lubricant to help with stuck nuts and such. The WD in the name actually means Water Displacement. By spraying this inside, it will keep water out of the cap and off of the parts. WD-40 is also non-conductive, so will help to eliminate carbon tracking, which can cause the engine to miss on one or more cylinders.

I am with you on this, though, thinking about you saying the engine will not start. Unlike the older HEI distributor, your distributor does not have the coil located in the cap. If I were a betting man, I would think you have some sort of grounding problem to the coil or the electrical connection to it is lose, corroded, or otherwise not allowing things to work right.

Answer 2

I've had this same problem with my suburban..put a starter button in it,replaced the starter..every time I took it to the shop the mechanic told me twice I had a stripped battery cable bolt, the one for accecories I asked him both times to replace it and both times he told me this would not cause the problems I was having with the truck...finally after having everything replaced that I could and the truck sitting for two weeks I decided to buy the damn battery cable bolts and replace them..guess what the damn thing started right up and has run for the past month with absolutely no problem..try for ten dollars changing the battery bolts in your suburban if one is stripped this will cause your truck not to start and will also burn up starters when it does start..if stripped they will cause not full battery getting to the starter and it having to work harder to start the truck..a good place to start..like I said it took fits sometimes it would start and other times no way..i kept telling everyone it was like I had a short in it..I DID THE BATTERY CABLE BOLTS..

Answer 3

After days of research on this exact topic I think I have an answer to fix our problem. To fix your problem I would first change the ignition coil and ignition control module. Both are next to each other and are attached to a small metal bracket bolted to the top of the motor just to the passengers side of the air intake/ throttle body. P.S. From the ECM comes a signal to ignite the spark plugs etc. This signal first goes through the coil and ICM. Then that signal is sent to the distributor cap through the short spark plug wire that basically powers the center pole of the cap. This signal then flows down into the rotor cap which makes contact with each spark plug and gives it the electricity to ignite or spark. P.S.S. If changing the ICM and coil does not help you may need to buy a new ECM/CPU. You can buy a new Electronic Control Module from an auto parts store but they can ONLY be checked by a dealership. ALSO, if you do buy a new computer, the car will need to be towed to the dealership so they can install the operating system on to the ECM and make sure it is talking to the engine properly.

Here is my story and why I was forced to research this problem...

Ok, we have a 1996 Suburban Lt with a 5.7L engine. We have had a few repairs but nothing this complicated before. We are driving down the interstate and suddenly the truck dies. We notice the ECM1 fuse is out, so I replace it.

Then I tried to start it and nothing so I figured I replaced it for no reason and never checked it again until after we had the car towed home. I could not hear the fuel pump and assumed we were not getting gas so we dropped the tank and replaced the fuel pump and fuel relay, no change. We then noticed there was no spark. We started checking everything with a multimeter. Everything seemed fine so we jumped to the conclusion the computer was bad. We bought a new computer and again no change. We then noticed the fuse again was out and changed it. The key was already in the on position because as I was putting the new fuse in it blew in my hand. That is when we started looking a wires.

After a day and a half we found the wires that go to the crankshaft sensor were up against the exhaust manifold on the passenger side. It was barely touching, but when I tried to move the wires the protective covering was glued. That is when I knew there was burnt wires. We then cut enough of the wires in both directions even though only the pink wire was burned to a dark brown color. This fixed the fuse from blowing. The cable wires holder had come open and the wires had fallen out and were able to fall onto the exhaust manifold.

Nice that we fixed the initial problem but still we were not getting spark to the engine. We then replaced the crankshaft sensor, distributor cap and rotor cap, no change. Last we paid to talk to a mechanic advisor online, he gave us a list of chores to do all day long checking stuff etc. Last he heard we replaced the ECM or CPU. He asked if the Suburban towed to the dealer yet to reprogram the ECM. We were like no but we changed the chip. He kindly informed us the chip didn't do much and that we had to have it towed to the dealer in person because the operating system of the vehicle is proprietary to GMC. So we had it towed to the nearest dealer and it was ready the next morning. They said the camshaft sensor pulled up a code and so a couple hours after getting the truck back we replaced it too...

Since, it has been driving better than when we first bought it in 2008. The only problem we have had is some bad gas due to some dirt or something from syphoning the gas into 4 cat litter buckets and 2 5-gallon buckets. I cleaned the containers out but who knows. the gas sat in the garage for a couple of days until the day we had it towed to the dealership.

Hope our mistakes and stupidity help others in the future. Lesson I learned is to not replace the main ECM/CPU so frivously.

Answer 4

the underlying problem is that its a design flaw. i have a 97 truck v6 vortec and every year i have to buy a new distributor cap. moisture, water whatever you want to call it gets in it and screws it up. it doesnt help that the ac line from back of compressor runs right over the top of distributor. all that condensate dripping straight down into cap. heck i was parked idling in the rain the other day and somehow rain got sucked up in it started missing warning light blinking....i was parked!! go buy another cap check the rotor and button and get ready to do it every year if u drive it a lot

Answer 5

the 96-99 suburban chevy 305\350 engine does have a flawed crab style distributor...the coil wire shorts with the number 3 plug wire contact at the distributor cap....if you're driving down the road and the vehicle stalls and wont start try pulling the number 3 plug wire...with any luck she'll start right up and get you home on 7 cylinders and then you can replace the cap...the rotor is fine as is the distributor. I've replaced everything...ign module, coil, ecm, its always just the poorly engineered cap....by the way the number three plug is the second from the front on the right side of the motor..i stumbled across the fix trying to get fire from the plug and the motor started...lol....a few months later on the highway it stalled and wouldnt restart...I pulled the wire and drove another 100 miles to get home and changed the cap...

Answer 6

Don't forget to check the easy stuff ... make sure the Distributor/timing is properly set on your car.