price said:
My 4.3 in an 89 Chev. 1/2 ton developed a full throttle miss ,backfire situation. I changed cap, rotor, wires, plugs and filter. No change. The truck ran ok at a very light throttle. We changed the e.c.m and it runs good now. Try it .If you can find one at the wreckers they are cheap. The tune up parts were costly and probably unnecesary.
Clint
I have the oppsosite story to tell.
I worked at a Ford dealership, and watched them fight for several months with a 98 Jimmy 4.3 Vortec.
It was (intermittently) mis-firing while cranking, and taking out starters, drives, and flex-plates. They (supposedly) spent hours of diagnostic time, replaced crank sensors, put in a used ECM etc ... to the tune of about $2500.00 worth of parts and labor, and had given the customer a loaner for a really long time.
They hired a new tech (one with better eyes apparently) that spotted a VERY small arcing track on the inside of the distributor cap. It was the cap that has the horizontal terminals on it ... looks like a spider.
Apparently it was cross-firing between 2 cylinders whenever there was a bit of condensation build-up on the inside of the cap ... hence the intermittent problem.
