Gm Tbi No Injector Pulse While Cranking

camaro_thunder92 · January 25, 2009

I am helping out a co-worker on this one. He swapped a 91 TBI 350 into an 85 chevy truck. The engine will run if you either spray starting fluid down the throttle body or hook up a remote start switch. If you use the key, there is no injector pulse while cranking. As you let go of the key and return it to the run position, the injectors give one squirt. Here is the checklist:

Painless wiring harness

Fuel pressure: good

Fuel pump primes when key is turned to run position

Plenty of spark under crank position

12v to injectors at run and crank position

No pulse while in crank

Like I said, the truck will start and run if we use a remote starter switch and injectors pulse. It will also start and run with the key if we use starter fluid or gasoline through the throttle body.

Thanks in advance for any help you are able to provide.

Heavy Cruiser · January 25, 2009

No START pulse to the ECM?

See if the colored injector wires are pulsing during crank - view the analog scale of the DMM - it reacts faster than the readout- or a bulb across the disconnected inj connector - one lead on the black wire, the other lead on other wire, watch the filament for pulsing.

GMTBI350 · December 10, 2009

BTT...

Any luck finding the problem? I'm having the same with my parents Suburban 5.7 TBI. It never started on the first try, but does on the second, or if you crank the engine for about 8 to 10 seconds on the first attempt. Everything is working great except there's no negative Injector pulse for the first 8 to 10 seconds. People have mentioned a "Injector Driver Module" between the injectors and the ECM. Not sure if this model year has one though or if there refering to the Ignition control module which leads me back to the Distributer and the Magnets again during start. I've seen a schematic showing the EST/ECM with a note "Above 600rpm after 5-15 seconds". Not sure what that Diagram is trying to tell me though. All I need is 1 second of negative injector pulse before I hit the starter and the truck fires up instantly.

camaro_thunder92 · January 26, 2009

There is no injector pulse while cranking. I used a Noid Light while cranking, and nothing. We do get pulse if we use a remote starter. For some reason, the ECM is not sending the injector pulse signal while the ignition switch is in the crank position.

chuckyou · April 15, 2011

Having the same issue with my truck 88 gmc 1500 and I see all these places where people are having it but no one says what they did to fix it.. Please help

wrencher · April 17, 2011

Check for a high throttle position sensor voltage, high TPS voltage at start can stop the injectors when cranking. It's used as a clear flood function when the throttle is held open during cranking. A quick test is to just unplug the TPS, that will set a fault code and the clear flood mode would be inhibited.