B2600i - has us totally stumped !
 

My '92 B2600i 4wd - great truck! - is very sick. Suddenly became almost undrivable - all the classic symptoms of a bad ecm. So we replaced the ecm - three times - as we understood that it's sometimes hard to find a good rebuilt one. No change. We learned about AV-PRO in Fort Myers Beach, Florida - they rebuild ecms - tried one of theirs. No change. It will start from cold and run until the temp needle starts to move and then it stalls, coughs, runs rich, no "check engine" light on the first ecms but on the AV-PRO one we get that light showing. Replaced the air flow sensor - no change EXCEPT - if we disconnect the air flow sensor it smooths out and idles normally but has no power if you try to drive it. SO - replaced the air flow sensor again thinking maybe we had a bad one. NO CHANGE. In the process we've checked every other sensor and timing and everything else we can think of. NO CHANGE. We're at our wit's end! Does anybody have any ideas?

rolomac

Exhaust. Clogged Catalytic converter. Not all cats have sensors.

Thanks for the suggestion - we'll check that today.

rolomac

so - - - we don't think it's the cat. As of now - if we disconnect the air flow sensor it runs but not real good. It's drivable but down on power, chugs a bit and hesitates. If we reconnect the air flow sensor it runs terrible - but it's a new sensor - matter of fact it's the second one - we returned the first new one thinking maybe it was a defect but the second one performs just the same. We're thinking maybe some sort of short in the wiring harness to the sensor?

When there is bad running engine conditions, it can lead quickly to cat issues. You may have other issues, but be wary of the cat also failing because of this.
Ever change the O2 sensors?
Why haven't you disclosed the mileage?
"we found two weak engine grounds. Their terminals had oxidized slightly on the aluminum intake manifold and were causing enough of a voltage drop in the ground side of the sensor circuit to keep the engine computer on guard."
This is why I always suggest installing extra grounds: to body, to engine block, tranny, throttle body.

READ: Causes of cat failure

O2 sensors: NGK Spark Plugs Canada » Tech Info » Oxygen Sensors

O2 sensors: Replace Oxygen Sensor - O2 Sensor Circuit Replacement

Wow! Lots of information - thanks

rolomac

If you think its the cat, just unbolt it and set it aside. Crank it and see what happens.