Engine died while driving & rpm jumps at idle

[Michael1784]

1992 GMC Sierra k1500 5.7TBI 5spd. Manual

For context here is a full rundown of everything that has happened;

It all started one day after work, I checked the oil which was fine and tried to start it but it wouldn’t crank. The dash lights came on as normal but once I turned the key over the starter made a light thump and the truck went dead.

Thought it was a dead battery so I got jumper cables on it and still was acting the same. I had to disconnect the ground from the battery for the dash lights to come back on after the no crank. I tapped the starter while my brother turned the key over and it fired right up, I took it on a test drive and it was running normal as before the issues started.

So I replaced the starter and the dead key issue still persisted, well come to find out a bolt for one of the battery terminals was messed up so I replaced it and it fixed that problem

I take it on another test drive to make sure everything is good to go. I go to the store, turn the truck off for a few minutes and it fires back up just fine, I sit and idle for a minutes then head back home. The truck runs fine until im almost home when I see the rpm gauge drop and the engine turns off, the lights did stay on. I tried to pop the clutch and it immediately starts and dies. When I get into the driveway I tried to start it again and it immediately fires up then dies.

Today it fired right up normal and ran fine for a minute before the rpm’s started jumping around, going from 0rpm trying to get to 1500rpm and it will stick around 1500rpm for a sec then go back down. The engine sounds fine mechanically so I’m curious what your guys thoughts are. I haven’t checked the IAC or vacuum lines yet. I have a video but I’m not sure of how I can post it here yet.

Has anyone else had this problem? Thank you for any info

TL;DR Truck didn’t want to crank, replaced the starter, ran fine for a few minutes then truck died and now RPMs jump.

Video of the RPM at idle vid is on YT unlisted

 

[Michael1784]

I’ve checked for vacuum leaks, ruled out the o2 sensor, rules out the IAC, checked all the spark plugs, rotor, cap, and wires they all looked good. The inside of the cap did have a bit of greenish buildup on some of the nodes so I cleaned that up.

I unplugged the brown wire that adjusts timing and checked the timing with my timing light, I noticed the #1 cylinder doesn’t fire every time and would be when the engine rpm bogged down then it would fire and rpm jumps up but eventually the engine would die out.

Thinking it’s the distributor now.

 

[docstoy]

Battery bolt messed up, what does that mean ? Sidepost or Top post ? Ckd timing and timing light not constantly flashing, do other cylinders do the same ? Any corrosion on inside of plug wire terminal/distributor cap towers ? Sta rt with these questions first

 

[Michael1784]

Battery bolt messed up, what does that mean ? Sidepost or Top post ? Ckd timing and timing light not constantly flashing, do other cylinders do the same ? Any corrosion on inside of plug wire terminal/distributor cap towers ? Sta rt with these questions first

The bolt threads were messed up so when it got tight it rolled back over to loose. There wasn’t any corrosion on the spark tips nor inside the wires I checked them all, but I didn’t hook the clamp over any other cylinders to be completely honest.

I read that the tach is connected to the coil which would show the rpm jump if the coil isn’t firing properly. When I took the cap off the dist. it looked a little corroded. It’s old old

 

[1998_K1500_Sub]

A jumpy tach can be indicative of a bad cap; another GMT member discussed an identical problem earlier this year.

 

[Zulu Kono]

Alternator.

 

[Michael1784]

The pickup coil in the distributor ended up being the problem. Replaced the distributor today and the issue is fixed

You must be registered for see images attach

 

[Schurkey]

Nevermind. Too late to be useful.