Help: 85 305 Suddenly Stalling in Gear

[Trucksareforwork]

Ok, here's the deal: 1985 C10 with a 305. No air pump or EFE, but all other vac lines are updated and intact. Truck has run like a champ for more than a year after a light restoration (thread elsewhere). I'm having trouble suddenly and wanted any quick ideas. The story:

The truck had to be parked outside for most of the winter after I lost access to some shop space. I drove it a few times, but not a lot. Maybe less than 100 miles.

Then, I suddenly started to get a stall situation while in gear and warmed up. Truck would warm up fine, then when I would get to a stop sign it would just...quit. I can't even describe it any differently. No sputter, no struggle, just...Off as if spark has just stopped.

I fiddled around and realized that my distributor hold down was a little loose, and so figured I had just slipped timing a little bit. Got out the timing light and re-set timing over the weekend. Ran good/great after that. I thought I had solved the problem.

Then today, I needed the long bed for a project, and figured what the heck, I'll take it out on the road. Got outside the driveway and... just stopped. Then couldn't get more than a sputter on re-start. Got pissed, left it there, came back in two hours and got it started (cold again) and pulled it back in the drive.

Any idea what could be causing such behavior? The Distributor seems plugged in well (my first thought was the pigtail getting intermittent), I THINK all the vac lines are intact...they were mostly replaced in 2022.

Is there something in the carb (quadrajet) that would cause this behavior after warming up? My other theory is perhaps a major vac leak related to one of the TVS's (since the issue shows up after warming up), but I don't hear anything. Anything else?

I'm just looking for ideas. Starts cold, then stall, then basically no start after the stall.

Thanks!

 

[viaminveniam1939]

I’m NOT at all qualified to answer this… could it be vapor lock?

 

[fast 99]

Shutting off first thing to check is spark. There are many issues that can cause it, but number 1 is module second would be a coil or pickup. If a moule is replaced use enclosed dielectric on base. Be sure and check for power supply at distributor first.

Without being there next would be a vacuum leak or bad idle circuit but the vehicle should at least re-start then die.

 

[Snoots]

If you have HEI, I would guess the pickup coil in the dizzy.

 

[Ricko1966]

1985 305 should be esc distributor the controller behind the glove box does funny stuff when they start to fail. I'll find the info on the bypass and post it in a few minutes short version I tell you how to make the bypass jumper,you keep it in the truck,next time it fails, put in the jumper.If the problem goes away we,'ll discuss ways to fix it,advantages and disadvantages.
Okay here's the info carry this pic on your phone and a piece of wire with each end stripped and roll of electrical tape in the glove box. In the pic this is the connector on the distributor side,unplug it from the harness coming out of the firewall and instead of cutting anything put your jumper wire into A and C ( black and green) tape it in place and see if that makes it run again.

 

[brooksman9]

Agree with Snoots. Had the same issue with a 79 Vette we had once. Pulled the distributor and replaced the ickup coil. Problem went away. Probably easier to just replace the damn distributor though unless there is something special about that one.

 

[Ricko1966]

Agree with Snoots. Had the same issue with a 79 Vette we had once. Pulled the distributor and replaced the ickup coil. Problem went away. Probably easier to just replace the damn distributor though unless there is something special about that one.

There is something special about that one. It should be esc. The 2 biggest failure points are the esc. controller and the module. In my expierience a problem that comes and goes with them it's the controller.

 

[Trucksareforwork]

I did replace the module but not the coil. Esc has been disabled. Would the coil failure happen with even a little bit of heat? I actually hadn’t thought of that. I usually think about the coil needing a lot of heat to show fail.

It’s a weird thing. It will start, idle high, then when it warms up if I put any load on it at all it just dies. No sputter, no fuss, just…”off”. That’s why I changed the ignition module originally. It acted like a spark problem.

BTW, I thought about idle circuit trash especially since the truck did this after sitting. But Wouldn’t trashy idle circuits be moot if I revved the motor?

I’m hoping to dig back into it this weekend. I did put the vacuum gauge on it and something seems off because I recall it idling when I first set it up at about 20 inches and now it’s at like 15 while at high idle. Then it died and I had to go to work.

I have spent only a total of about 20 mins chasing this so no frustration yet, just was looking for likely candidates. My next step is to block off all vacuum ports except advance and see if that isolates the issue, and then if not I will do plugs and coil and check the idle circuits.

 

[Trucksareforwork]

Tried new coil. no change

Opened fuel line to check for obstruction at the q jet. No change.

Ran down all vacuum lines and double checked them. While also:

Using a screwdriver to gently actuate the egr valve.

That seems to have fixed it. I’m wondering if I had a stuck egr valve. The issues cropped up after it sitting for a long time.

Just wanted to offer thread closure.

 

[Trucksareforwork]

Opening up this thread to close it again. Stalling started again.

Removed EGR, no problem with it. It was a placebo. I guess I jiggled it last time and the engine came back to life at the same time but not because of.

Lost all fire to plugs. Suspected pickup coil this time.

Swapped out distributor, fired fine. That was the solution. I assume it could be the pickup coil that was going bad, but don't know because it didn't make sense to keep buying distributor parts when I could just swap in a new disti.

 

[ChuckN]

Check your fuel filter? Just an idea.

 

[Matt69olds]

Guess this is useless info no that it’s fixed. But maybe someone else will find it useful.

https://www.gmcmi.com/wp-content/uploads/2014/05/HEI-Testing.pdf

 

[Trucksareforwork]

Guess this is useless info no that it’s fixed. But maybe someone else will find it useful.

https://www.gmcmi.com/wp-content/uploads/2014/05/HEI-Testing.pdf

That is a great resource. I will still use it to fix my old distributor if I ever get around to it.