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GMC Expert
GMC Expert, ASE Certified Technician
Category: GM
Satisfied Customers: 10370
Experience:  30 yrs experience, ase certified, shop owner
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1992 GMC Sierra 1500: 4WD..idles..runs rough..It stalls in reverse

Customer Question

My 1992 GMC Sierra 1500 5.0L 4WD truck idles and runs rough. It stalls in reverse as if not enough gas is feeding and sometimes talls when moved from reverse to drive. At a stop, I need to move the gear to neutral to avoid stalling. The exhaust smells of gasoline. I've changed the EGR, PCV, O2 and MAP sensors, vacuum hoses to/from EGR, PCV, & MAP, all spark plugs, wires, distributor cap and rotor, Air Idler Control unit, gas filter. What more can I do without taking it to a shop?
Submitted: 7 years ago.
Category: GM
Expert:  GMC Expert replied 7 years ago.

MOST OF THE TIME THIS IS CAUSED BY A FAULTY DISTRIBUTOR

HERE ARE A FEW TESTS TO DO AND LET ME KNOW WHAT YOU FIND

Tests/Procedures:1. Remove the distributor cap and disconnect the pick up coil wires from the back of the ignition module.

2. Place a voltmeter set on the AC scale across the two pick up coil wires and crank the engine.

3. The pick up coil should produce at least 0.7 volts AC.
Potential Causes:Distributor Shaft
Pick-Up Coil
Tech Tips:If voltage is less than 0.7 volts AC cranking, replace the distributor shaft and pick up coil together.

Customer: replied 7 years ago.
Thank you for the information. A friend installed a new distributor, ran some meter tests on the wires at the distributor and then near the spark plug, found #2 reading differs at each end. Tested #4, no problem. Attached a compression gauge to #2 & #4, both registers good. He's baffled as to why the reading differs on #2 at the distributor end of the wire. Advancing & retarding adjustments didn't help. Hence, still no cure. He suggested I replace the coolant sensor unit and install a thermostat. Engine was running without a thermostat for a few years because of overheating (Hawaii weather). Still no cure. Engine still runs like its running out of gas and the exhaust smells of gas. After all these parts replacements, will replacing the ECM now finally do the trick?
Expert:  GMC Expert replied 7 years ago.

YOU SEEM TO HAVE EITHER BAD INJECTORS OR BAD ECM

I WOULD LIKE THE READINGS FROM THE O2 SENSORS

AND MEASURE THE INJECTOR PULSE WIDTH AT THE INJECTORS