1977 GMC Sierra truck runs but stalls

77SIERRA4X4

MEMBER
1977 GMC SIERRA

I have my 77 sierra classic 4x4 powered by a 350 small block chevy running on a propane setup and the problem I'm having but cant figure out is that whenever I go to drive my truck it fires up fine and everything, I let it run to warm up and ill walk away to go do something and I come back and the motor is off and everything is still on volt meter (gauges) stereo, key is on the on position. I stayed in my truck the next time and fired it up and noticed right before it stalls my voltmeter goes to zero then the motor shuts off, then I turn it over again and nothing, then Ill crank to key to acc then back to start then the battery gauge registers then the motor cranks and turns over and ignites. Cant figure it out
Thanks in advance
Antonio

1 Reply

CARADIODOC

MECHANIC
33,873 POSTS

Given your observations it sounds like there's a bad contact on the ignition switch or an intermittent connection related to its wiring. Besides the gauges and ignition system there are typically other things on the same circuit so you might look for a dead heater fan motor, radio, power windows, and things like that.

Start with a visual inspection and look for blackened or overheated terminals, melted connector bodies, corroded splices, etc. You may have luck connecting a test light to the switched wire so you can monitor where you lose the voltage when the problem occurs. If the test light goes off when the problem occurs, move it to a point closer to the ignition switch and try again. If the light stays on when the problem occurs, the cause is after that point.