Ran fine, next day runs like crap (V 6 vortec 4.3)

10

Asked by Jan 29, 2014 at 08:21 AM about the 1994 GMC Sierra 1500

Question type: Maintenance & Repair

Fuel tank was in the last quarter. Timing mark is jumping all over the place. Only keep it running
if I keep my foot on the peddle. Eyeballed the dist. at #1 position and vib damp mark seems to
be TDC. Pulled the plastic ring on  carb and the two fuel injectors seem to be putting out the
same & equal fuel skirt on both. Dist. is electronic. Computer comes back with all 12's.
Temp.50/60 nite,70/80 day. No sensor on timing mark guide. Dist.wires are correct order.
Seems like timing to me. Runs like timing jumped a tooth or plug wires are crossed. Is there a
fuse that would cause this or a sensor? Computer? Blocked exhaust?  Spark plugs go out that
fast? Electronic Dist. do you TDC from plug wire?  (What is extra line on vib damper.) Water in
fuel (Hard to believe) Thanks Pete

3 Answers

111,045

If you feather the gas pedal will it seem to run ok? If so it's probably the idle air control valve either dirty or faulty. Could also be the throttle position sensor.

111,045

Symptoms of an Idle air control valve not operating properly are loping idle(high then low), high idle, low idle or going dead at idle. If yours is doing any of these things and you can give it some gas and it will seem to run ok then I would check into either cleaning or replacing the idle air control valve.

10

Does not make any difference at what rpm you hold it, it till runs the same. Talking to a neighbor and he suggested a head gasket. So far I have replaced plugs, wires, cap and rotor. To me it still sounds like it is missing on at least one cylinder. A timing gun placed on all six wire shows that they are all firing. Also, idle sb about 600 rpm but your right, it is going dead at idle. sure hope neighbor is wrong about head gasket.

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