Hey all. Been pulling my hair out over my truck. 1990 k1500 350 TBI. Pops out the exhaust and smokes black upon startup. I can barely get it to run sometimes and when it does it appears to do better at higher rpm but popping is still present. If I unhook the est bypass wire idle is great and truck runs good but mpg and power are not at normal levels. GM Tech 1 data all looks normal but keeping truck running with wire hooked up is tough so not sure how accurate that is. Probably cant keep it running long enough for dtc to set. I have replaced plugs, wires, cap and rotor to no avail. No big loss there as it was time for them anyway. Also have tried different distributor assembly, ecm, est module, map sensor and knock sensor. running out of ideas and the whole unhook the est wire and truck runs fine is causing me to chase my tail. Any ideas?

 

What is the ignition timing at idle with the wire connected, and what is the timing with it disconnected?

 

I have tried between 2 degrees retarded and 8 degrees advanced with wire disconnected. Cant seem to keep it running long enough with wire connected to get measurement.

 

When the est wire is unhooked is only the timing affected or will the ecm revert to a base fuel map also. I believe I've only checked the ect readings while the engine was running with the wire unhooked and am wondering if it goes to a default value under those conditions. Won't be able to get the truck back on the scanner for a week or so but it would be easy enough to bypass the ect and see if that changes anything.

 

Check fuel pressure and check the distributor itself. Mine had a similar problem and the internal distributor parts just crumbled when i check it.

 

Fuel pressure was 11psi and I have swapped distributors with one from a running truck. It is overfueling for sure when the est wire is connected. I was under the impression that only the timing was affected by disconnecting that wire but it is definitely affecting the amount of fuel that is being injected.