1985 K20 350 Lost Spark While Driving

[klarster]

Sucker fell on its face mid-drive again. Good news is this time I'm still getting fuel! Bad news, no spark. I was thinking this unique bit of information might be the key, or maybe not, but it stood out to me: Initially when I coasted to the side of the road, I could shut off the key, then crank it and it would fire once or twice but never fire up. It did this the first three or four times and I've had zero spark since. Towed it home, pulled the cap and the contact points were TOAST. Hideous. Replaced cap and rotor by instinct because they looked so horrible but may have jumped the gun, cause I still have zero spark. "Hot" wire from key to coil has 12volts, and coil has 12 volts coming out. Coil resistance tests well within acceptable limits. What else could cause disappearing/no spark?! In another thread I heard tell of a mythical item called an ignition module/ignition control module. Could this be the cause of all my woes? Where does it live and how do I find out how healthy it is? As always, thanks in advance for y'all's expertise/assistance. You're the best!

 

[wlwarnke]

HEI are normally pretty darn dependable.

Did you look at the button that connects the coil to the rotor and the rubber insulator that it sits on?

The ignition module sits in the base of the dizzy under the rotor. Little 1/4 round module with 2 two pin connectors on it. I’ve had them go flaky and cause some really strange behavior. Loss of spark, intermittent surging, etc.

I’ve also had the +12v wire come loose from the cap and shut her down at 70mph.

 

[fast 99]

contact points were TOAST. Hideous.

Is it HEI or points?

 

[klarster]

Is it HEI or points?

HEI I believe. I'm not horribly familiar with such things just yet. Still learning!

 

[wlwarnke]

Should be HEI if stock.

Coil is integrated into the cap.

 

[wlwarnke]

Is it HEI or points?

I read his quote a few times also and deciphered it as the cap and rotor contacts.

 

[klarster]

UPDATE: I did get a chance finally to get in and replace the ignition module a couple days ago; still no spark. What else could cause the type of problems I'm experiencing? I just really need to get this thing running reliably so I can get some much-needed work done on my DD Jeep but I have yet to establish if this truck is anything more than a freaking lemon... I've had it for 5 months and haven't gotten to put more than 200 miles on it between all these issues! I heard tell of another mythical device known as a pickup coil. Can this cause intermittent/permanent loss of spark? Where is it located in an HEI system?

 

[wanderinthru]

Does it have a tach?

 

[Bextreme04]

UPDATE: I did get a chance finally to get in and replace the ignition module a couple days ago; still no spark. What else could cause the type of problems I'm experiencing? I just really need to get this thing running reliably so I can get some much-needed work done on my DD Jeep but I have yet to establish if this truck is anything more than a freaking lemon... I've had it for 5 months and haven't gotten to put more than 200 miles on it between all these issues! I heard tell of another mythical device known as a pickup coil. Can this cause intermittent/permanent loss of spark? Where is it located in an HEI system?

Start with the basics. Does the rotor turn when you crank the engine with the cap off? How do you know you are getting fuel? How did you check that you are getting spark? Did you run a compression test?

The pickup coil can be seen when replacing the ignition module, it is a little spiked wheel on the distributor shaft under the rotor. It spins with the distributor and the teeth cause a signal to be picked up by a little magnetic sensor in between the teeth and the ignition module. If the teeth get worn down somehow or the pickup coil gets damaged, it wont tell the ignition module when to fire the coil.

Post pics... they help

 

[AuroraGirl]

heres some HEI distributors for pics of what they may look like inside

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You must be registered for see images attach

 

[klarster]

It does have a tach, single green wire coming off the coil then through the firewall.

Start with the basics. Does the rotor turn when you crank the engine with the cap off? How do you know you are getting fuel? How did you check that you are getting spark? Did you run a compression test?

The pickup coil can be seen when replacing the ignition module, it is a little spiked wheel on the distributor shaft under the rotor. It spins with the distributor and the teeth cause a signal to be picked up by a little magnetic sensor in between the teeth and the ignition module. If the teeth get worn down somehow or the pickup coil gets damaged, it wont tell the ignition module when to fire the coil.

Post pics... they help

I hadn't thought to spin the engine with the cap off, that'll be on my list for next week! I can smell fuel after cranking. I pulled each individual spark plug and checked each for spark. I also hadn't thought to run a compression test. It sounds the same cranking now as when it was running so I hadn't thought about it. I do have a test gauge though so I'll definitely be confirming that next week as well. What should my compression most likely be at/around? I know it does have some blowby, so it's probably not factory spec. Is there any way to test the pickup coil, or is it easy/cheap to come by at the friendly neighborhood parts store that it wouldn't hurt the pocketbook to just replace? This is all very good stuff, thanks everybody for input!!

 

[Bextreme04]

It does have a tach, single green wire coming off the coil then through the firewall.

I hadn't thought to spin the engine with the cap off, that'll be on my list for next week! I can smell fuel after cranking. I pulled each individual spark plug and checked each for spark. I also hadn't thought to run a compression test. It sounds the same cranking now as when it was running so I hadn't thought about it. I do have a test gauge though so I'll definitely be confirming that next week as well. What should my compression most likely be at/around? I know it does have some blowby, so it's probably not factory spec. Is there any way to test the pickup coil, or is it easy/cheap to come by at the friendly neighborhood parts store that it wouldn't hurt the pocketbook to just replace? This is all very good stuff, thanks everybody for input!!

My truck just died going down the road while hunting last year. Spent a bunch of time beating around the bush because I could smell fuel and the plugs looked wet, so I assumed I was getting fuel. Finally after eliminating everything else 2-3 times I went back and VERIFIED whether I was getting fuel. I was not. Fuel pump lever had broken off. Disconnect the feed hose to your carb and stick it in a clear bottle. Crank for a few seconds and see if you have lots of fuel in the bottle. If not, you have a fuel issue.

Compression should be between 100-150psi. All cylinders should be within 5-10 psi of each other. Anything under 100 psi is a dead cylinder.

My comment on looking at the rotor while cranking is simply to make sure the distributor gears aren't totally trashed and that the timing chain is still present/connected. It's not likely failures, but still should rule it out.

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[klarster]

My truck just died going down the road while hunting last year. Spent a bunch of time beating around the bush because I could smell fuel and the plugs looked wet, so I assumed I was getting fuel. Finally after eliminating everything else 2-3 times I went back and VERIFIED whether I was getting fuel. I was not. Fuel pump lever had broken off. Disconnect the feed hose to your carb and stick it in a clear bottle. Crank for a few seconds and see if you have lots of fuel in the bottle. If not, you have a fuel issue.

Compression should be between 100-150psi. All cylinders should be within 5-10 psi of each other. Anything under 100 psi is a dead cylinder.

My comment on looking at the rotor while cranking is simply to make sure the distributor gears aren't totally trashed and that the timing chain is still present/connected. It's not likely failures, but still should rule it out.

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Now I see why you were so adamant about making sure I was sticking to the basics! I did put a brand new fuel pump and all-new lines in when I bought the truck 4 months ago, and cleaned the tank and fuel pickup really good at the same time. Fuel sending unit and carb were new about a year before I bought it. All of that leads me to say I'd BETTER be getting fuel but I'll still personally confirm it. It sounds like you had a hell of a nightmarish time figuring out what your problem was and I kinda feel like that's how it's been for me this time! I will also say that there was resistance in the distributor shaft when I was removing and replacing the cap/rotor but I'll still confirm it actively spins with the engine.

 

[Bextreme04]

Now I see why you were so adamant about making sure I was sticking to the basics! I did put a brand new fuel pump and all-new lines in when I bought the truck 4 months ago, and cleaned the tank and fuel pickup really good at the same time. Fuel sending unit and carb were new about a year before I bought it. All of that leads me to say I'd BETTER be getting fuel but I'll still personally confirm it. It sounds like you had a hell of a nightmarish time figuring out what your problem was and I kinda feel like that's how it's been for me this time! I will also say that there was resistance in the distributor shaft when I was removing and replacing the cap/rotor but I'll still confirm it actively spins with the engine.

When mine failed, it was a brand new carter pump on a freshly rebuilt engine. Less than 500 miles and less than two months old.

 

[klarster]

When mine failed, it was a brand new carter pump on a freshly rebuilt engine. Less than 500 miles and less than two months old.

Unacceptable!! Let's hope that's not my case this time... Updates to come! I'm traveling out of town for work for the next week beginning tomorrow so next weekend will be the next time I can visit it