Random Loss of Spark - Please Help

[Alexf2002]

Re-reading your first post - every time you've worked on it, it got better for a while then deteriorated again. Is there a bad connection somewhere that when you work on the truck you somehow manage to make more complete and thereafter it loses its ability to conduct until messed with again? Or a heat path?

That’s kinda my current running theory. Lots of people have told me that it’s a bad ground somewhere which is why it’s not a consistent problem. I checked the block ground straps and they seem fine.

does anyone know of any specific grounds or ground posts that could cause the issue that I should check?

 

[Pinger]

That’s kinda my current running theory. Lots of people have told me that it’s a bad ground somewhere which is why it’s not a consistent problem. I checked the block ground straps and they seem fine.

does anyone know of any specific grounds or ground posts that could cause the issue that I should check?

In that scenario I'd look to see if I could slave in another ground in parallel - even temporarily. A lead with crocodile clips (like small jump leads) - that sort of thing. And hook it up to anything suspected of having a poor ground.

As an aside - definitely not referring you back to the HT side of things - years ago I was working on an engine (Redex treatment down the spark plug holes) and when I went to start it up - no joy. Tried a load of things over a few days until I replaced the king lead and it fired straight up. My point is that it is very easy to finish off something that was on its last legs but still working until disturbed. I suspect you have a similar thing - but reversed - if that makes sense!

Going slightly leftfield - is there any possibility that something has been slaved from the hot wires feeding any ignition component that could (when switched on) drag the voltage down and cause no-spark? Or on the circuit that energises the starter solenoid (given your lack of spark coincides with cranking but may not actually be the cause of the motor quitting when running)?

What year is the truck?

 

[Alexf2002]

What year is the truck?

1998 k1500 5.7 vortec

 

[Pinger]

1998 k1500 5.7 vortec

With PassLock?

I've been hearing about when PassLock goes bad and your symptoms seem to be the same as yours re the quitting but AFAIK PassLock cuts fuel not spark.

 

[HotWheelsBurban]

With PassLock?

I've been hearing about when PassLock goes bad and your symptoms seem to be the same as yours re the quitting but AFAIK PassLock cuts fuel not spark.

Yes that's what it does, cuts power to the fuel pump relay so the fuel stops. I'm in agreement with you on the grounds or something with the distributor or wires. Random electrical problems like this are so frustrating, and patience enough to see what it finally takes to fix it can be hard to find. Been there, done that.....hang in there and you'll get it sorted out. Have you checked the ignition module?

 

[Alexf2002]

Yes that's what it does, cuts power to the fuel pump relay so the fuel stops. I'm in agreement with you on the grounds or something with the distributor or wires. Random electrical problems like this are so frustrating, and patience enough to see what it finally takes to fix it can be hard to find. Been there, done that.....hang in there and you'll get it sorted out. Have you checked the ignition module?

I had a bad ignition module in the beginning of this journey that I replaced and I recently had the new one tested at autozone when this issue started. It passed all their tests. I haven’t checked the harness plug thoroughly. The main problem is my issue doesn’t consistently happen so it’s hard to check things for issues if the problem isn’t occurring

 

[HotWheelsBurban]

I had a bad ignition module in the beginning of this journey that I replaced and I recently had the new one tested at autozone when this issue started. It passed all their tests. I haven’t checked the harness plug thoroughly. The main problem is my issue doesn’t consistently happen so it’s hard to check things for issues if the problem isn’t occurring

Understood! That's what makes these random things so much fun to diagnose. It might be a wire that's touching something it shouldn't from time to time, causing your problems. A lot of crazy electrical problems end up being something little like that, in my experience.

 

[Alexf2002]

Understood! That's what makes these random things so much fun to diagnose. It might be a wire that's touching something it shouldn't from time to time, causing your problems. A lot of crazy electrical problems end up being something little like that, in my experience.

It’s crazy how inconsistent it is. Took the truck for a spin today to see if I could get any issues or codes or something and after 30 miles worth of driving it had nothing go wrong and ran like new.

 

[HotWheelsBurban]

It’s crazy how inconsistent it is. Took the truck for a spin today to see if I could get any issues or codes or something and after 30 miles worth of driving it had nothing go wrong and ran like new.

It's like when your kid says they're sick but you get them to the doctor and they are fine, then the nest day or two they really do get sick. Bad simile for these times, but true more often than not. Good luck with it, and let us know what eventually fixes it. We all benefit from finding out the cause of the problem; one of the other members might have it next week...thanks

 

[Donald Mitchell]

Something worth taking a look at is the icm connector. I went thru this several years ago and after spending money and time on a mechanic I dug into it myself and found the connector badly corroded. I didn't buy a new one just cleaned it and it worked.