Hi

I have a '94 GMC Jimmy (4.3l) that has been exhibiting odd electrical behavior over the past four months.

It intermittently will not fire up. The engine turns, I have electricity in the cabin, I get gas pressure, but I do not get spark... very intermittently.

I think i've narrowed down the event to a forward incline. So far it cranks every time when flat or facing downward. Everytime I can remember a failed attempt it was tilted upward in some way.

It doesn't appear to be weather related, internal temp or external temp related. It happens rain or shine, first thing in the morning or middle of the afternoon. With an overnight break or ten minutes after driving. When it fails, it may crank up after the second or third try, or it may be days later.

Here's what confuses me (well actually I am totally confused now). Even when it is on a forward incline, if I give it a couple days it will crank up. Or, If I am able to let it roll down the hill and turn it around so that it is facing down, it will crank up.

But then again. It will run and crank for weeks at a time without issue (even with a front incline at shutoff), or sometimes it will fail me more than once in a day.

It has never died while driving, and once it's cranked it can be on whatever incline I want it to and it will run fine. Angle doesn't seem to cause an issue once it has started up. we have hills here, some are 6% and 7% grades.

I have replaced the following things trying to narrow this down. It has bewn so intermittent it's hard to do:

Fuel pump
Fuel Filter
Distributor cap and rotor (it was time)
Ignition Coil
Spark plugs and wire (it was time)

I've checked the battery terminals and they are good. The Battery is less than a year old and provides power well.

It's worked for me the past three days, so if you are able to respond I may not be able to test your suggestion until it fails.

Any help would be greatly appreciated.
thanks

 

Just throwing it out there, but ICM? That is something that can be removed and tested at an auto parts store so you do not keep on throwing money into it like you have been doing.

 

So, I've replaced the ICM and the starter now. It fired up every time while sitting for two days before I was brave enough to drive it. I drove it after 20 good cranks and it refused to fire up at the first place I drove it to.

There is no spark. I disconnected the Ignition control module and hooked it back up and checked to wire from the ignition coil to the distributor.

It's been a couple days and it has successfully cranked one time since then.

ICM: new AC Delco
Starter: new Bosch

Any other suggestions would be appreciated.

 

Clean grounds?

 

Well, the battery terminals are clean anyway.

 

Hi everyone,

I just wanted to give an update and try to get some more feedback if possible. I am currently in the same situation. I can crack it once or twice a week and get it to fire up. Here is what I have done since I last posted/ partially gave up...

1. Checked all grounds I can find. Everything looks good.
2. Replaced another Ignition coil. This one is an AC Delco (truck continued behavior of cranking then not.)
3. Had the ignition control Module checked at a shop. They tested it 5 times and it passed every time.
4. Took it to a mechanic. He traced it to the ignition coil and I replaced it again... this time with an Carquest BWD.
5. Tested the positive wire to the coil... good. Tried to look for a negative control.?. I couldn't get my 12v light tester to show one, but maybe I'm doing it wrong.
6. tested the continuity on the wires going from the ICM to the Coil... pass
7. retested Distributor cap, and rotor tip. Good.

I bought an inline spark tester. It fails at the coil. I am thinking of paying a mechanic test the pickup coil on the distributor to see if the problem lies there.

I would appreciate any thoughts you could give.
thanks

 

Like you said in first post your getting power and its turning just not starting on a uphill
But no problems with flat and downhill Spark isn't a issue It's something that moves easy like a fluid Have you done a fuel pressure test? Try it on a flat then on the same hill The gauge is cheap and if you return it after (say you bought the wrong one ) you get your money back Some places might rent it to you It might not be a Fuel pump or fuel filter I replaced my fuel pressure regulator awhile back Also known to fail is the Spider injection there was a upgrade offered But my Blazer is a 05' and they came with the upgrade being the last year ...Let us know how it turns out. And lastly how much fuel is in the truck? anything at half and under might do this aswell

 

Sorry, I need to see if I can update the first post. It originally was only observable on an incline because it was rare and hard to replicate. As time has passed I have been able to replicate this at any degree of angle whether flat or not.

Regarding a fuel pressure test. I will buy the tool. I have only released the valve to see if I had pressure and that was successful.

Thanks