Motor Dies While Driving

[cfitz95]

My 86 K10 has a 350 with HEI. I was driving for about 30 minutes and then the motor died while cruising around 40mph. I pull off to the shoulder, throw it in park, and it fires right back up immediately and idles perfect. I drive maybe another 100 feet and it dies again. Same thing - throw it in park, start the motor up, drive about 100 feet and it dies. Did this many times, sometimes the motor was harder to start, but most of the time would start up no problem. It idles perfectly fine and only dies while driving/accelerating. It has good vacuum at idle, it has fuel, and battery is showing 14.6V at idle. I'm almost positive it is an ignition issue because when it dies, it doesn't stumble or cough like it is out of fuel. It cuts out and dies immediately like the key was turned off (sometimes backfires out the exhaust after it dies). I tested resistance on the coil and it checks out fine. All the plug wires are good and not arcing or cracked. Would this point to the ignition module or pickup coil? Any help is appreciated!

 

[chengny]

My 86 K10 has a 350 with HEI. I was driving for about 30 minutes and then the motor died while cruising around 40mph. I pull off to the shoulder, throw it in park, and it fires right back up immediately and idles perfect. I drive maybe another 100 feet and it dies again. Same thing - throw it in park, start the motor up, drive about 100 feet and it dies. Did this many times, sometimes the motor was harder to start, but most of the time would start up no problem. It idles perfectly fine and only dies while driving/accelerating. It has good vacuum at idle, it has fuel, and battery is showing 14.6V at idle. I'm almost positive it is an ignition issue because when it dies, it doesn't stumble or cough like it is out of fuel. It cuts out and dies immediately like the key was turned off (sometimes backfires out the exhaust after it dies). I tested resistance on the coil and it checks out fine. All the plug wires are good and not arcing or cracked. Would this point to the ignition module or pickup coil? Any help is appreciated!

I would have to agree - that it is an electrical problem associated with the ignition system. But in my (limited) experience, electronic components don't keep coming back to life. Try this easy diagnostic:

It will tell you whether the distributor has an internal problem - or the issue is loss of power to the coil primary side. Just run a temporary external jumper to the BAT terminal on the cap. Where the power comes from is not important - as long as it is independent of the ignition switch and the interconnected wiring. Just run it to the firewall junction block for example. If the problem goes away...you're dropping power to the coil primary. If it persists... there may be a problem within the distributor itself (e.g. the ICM or pickup coil). This test might not specifically identify the problem but may help save you some time & $$.

 

[cfitz95]

Interesting, I’ll definitely give that test a try tomorrow. I’ll report back my findings. Thanks!

 

[75gmck25]

I've also heard of a few folks having problems with an HEI cutting out from the movement of the vacuum advance mechanism. I'm not sure if it hits wires, shorts out, or whatever.

The easiest test for the advance would be to disconnect the advance can, run the engine up to cruising RPM so the mechanical advance has started to move, and then pull vacuum on the advance so that it moves the mechanism back and forth.

It might also be a fuel problem, since at cruise you are pulling a lot more fuel from the bowl than at idle. If there is a piece of rubber hose or other junk partially blocking the flow, you might suck the bowl dry quickly at higher RPM, but stlll have enough flow to let it idle normally after a restart. You could test for this problem by just running it at about 2000-2500 RPM for a few minutes while parked to see if it seems to run out of fuel. It will be noisy, but won't hurt anything. I've run it at 2500 RPM like that for quite a while during cam break-in.

Bruce

 

[mgarland]

Sounds like an ignition problem to me, I've had a couple Of hei's do this to me, they would be fine until they would get heat soaked after running for a while. Since you already checked the coil and it ohmed out correctly then I would put a pick up coil and module in it. If you have an old hei laying around just swap it out and see if that makes a difference.
Mark

 

[mags468]

Fuelpump relay. I went through alot before I found mine was bad.

 

[Big Chip]

Fuelpump relay. I went through alot before I found mine was bad.

86 had a mechanical fuel pump and a carb.

 

[WHEELMAN]

Most times ignition module.i doubt it would keep cranking up.if it was the fuel pump.a manual pump.

Don't forget to use the grease under the module.

 

[buildin64]

I had the same thing going on. I finally figured out that I didn't need to pull over to the side of the road. Just take your foot off the throttle, put the trans into neutral, turn the key off quickly and restart. Don't pump the throttle or it will most likely backfire when it restarts as there will be raw fuel in the bowl.
When I had the time I changed out both the ignition switch at the bottom of the steering column that is an electrical connection that is actuated by the key cylinder and the ignition module that sits on top of the distributor. As someone earlier mentioned make sure to use the electrical grease. You may want to also change out the distribution cap itself.
I did all of this at the same time since I bought the truck used and didn't have a clue as to the last time any of it had been touched. This cured my problem. Hope it works for you.

 

[peats]

i couldn't believe this post when i read it because my fresh frame on resto on my '81 c 10 360/th350 is doing the exact thing!it feels like it is running out of gas and will limp along at just off idle but will not take throttle. any input is welcome. sorry to barge in on this post but i could use some imput.

 

[Wumbo]

i couldn't believe this post when i read it because my fresh frame on resto on my '81 c 10 360/th350 is doing the exact thing!it feels like it is running out of gas and will limp along at just off idle but will not take throttle. any input is welcome. sorry to barge in on this post but i could use some imput.

If it will idle, but bogs when you try to accelerate, it's probably fuel related.

Start with a new fuel filter.

 

[peats]

everything is new including the gas tank,fuel pump and carb.

 

[Wumbo]

everything is new including the gas tank,fuel pump and carb.

How many miles since the carb was installed?

Last week I had the same problem. Good idle, but stumbling off idle. Hard to accelerate. New fuel filter with about 600 miles on it. This is a quadrajet with the filter on the inlet of the carb.

Pulled the fuel filter. Outside looked fine. Cut it open to find fine black particulate, which I can only assume to be fuel line deterioration. Replaced the fuel filter and it ran fine. Then I went ahead and replaced all the rubber fuel lines, tanks, and selector valve.

This truck had sat for several years, and that could have contributed to the fuel lines condition.

For $2.00 though, I would change the filter and see if it fixes it.

 

[peats]

mine is a new build with only 30 miles on it but checking the fuel filter is a good place to start. i use the stone filters

 

[73c20jim]

Bad ground somewhere???