79 k10 th350, Dies when put into gear

[Silver84k5]

Been searching some, but my issue seems a little different from the other thread i saw in here.

Truck ran and drove fine, then all of the sudden at a stop sign it died. Started back up fine, went to put in Drive, and died again.
Truck starts up and idles fine, revs fine in park, I tried putting the T case in neutral, then putting the trans in drive and it stays running just fine.
Vacuum advance seems to be working, (i sucked on the hose and the Rpms climbed). Vacuum hose to the modulator on the tranny seems ok, (no change when unplugged)
I Can keep it running in gear if i feather the gas pedal some while going into gear, but when accelerating it runs like crap until you get moving some, then itll run and drive normalish.
I put a spare Distributor in it just for testing, and the issues remain the same.

Ive had trucks run wayyy crappier than this and still wouldnt just die when going into gear. so Im kind of at a loss at this point.

Any advice is appreciated, thanks.

 

[dsteelejr]

Three things come to mind.

First is fuel delivery. Clogged fuel filter, clogged fuel lines, old rubber fuel hose with cracks allowing it to suck air, bad or weak fuel pump not supplying enough fuel under load.

Second is a vacuum leak.

Third is timing and idle speed. I know you said it ran fine before, but it’s possible the distributor wasn’t clamped down tight enough and it starts ‘dancing’ when the hold down clamp gets a little loose. I would recheck your distributor clamp tightness, recheck timing and idle speed first just because they are simple to check and you don’t need to start tearing everything apart to do that. Your idle speed should be set while at operating temp and in drive. Would be a good time to also check to see if advancing the distributor helps. If makes the problem go away you it know it was timing related.

 

[Silver84k5]

Fuel filter is newish, as in 6 months or so. looks pretty clean, mechanical fuel pump is also fairly new, I kind of wrote the fuel system off because it idles and revs fine in neutral, but i can give it a closer look.

I initially thought vac leak as well, i was gonna replace the vac lines and caps on the carburetor just because...

Distributor was definitely clamped down well when I went to remove it. When the engine is warm it starts up nice with a click of the key, the timing might not be dialed perfect, but I think it should be close enough that the engine wouldnt die under minimal load. The truck did seem to run better when i put the spare distributor in it though, just sounded smoother.

thanks for the suggestions.

 

[fast 99]

Does sound like a fuel issue. Didn't say what carb? Check fuel pressure and volume. Its possible crud got in an idle circuit. Take idle screws out, squirt in a little carb cleaner and reinstall the screws where they were. Check vacuum leaks.

 

[fast 99]

dupe