The Stovebolt Site Forums The Shop Area Engine Shop TBI swap injector problems

I have recently put a 1989 350 TBI motor in my truck. I have attached all the whistles and dimes, but when I go to turn it on; the injectors aren't getting any signal to spray fuel.

I have a new pump and it works well, so its not a fuel problem.

All the sensors I could think have been checked, I just can't seem to figure it out.


I need your help!

Make shure the ignition system is working. It seems to me the fuel system is set up so if there is no spark the injection system won,t work.

Its been a few yrs, but seems I had one w/a bad module in the dizzy that gave no fuel but a very weak spark-the injectors got their signal from the distributor. New module & bam, fired right up.

could it be anything else, my ignition module tests out just fine

Do you still have the ALDL & check engine light? try flashing the dash light for codes if so. Are you sure evrything is plugged in good? Sometimes after unplugging & yanking around while removing/installing an engine etc., those small metal terminal ends on Weatherpak connectors get bent, then when plugged in that terminal won't make a connection on one or two wires.

Bad or shorted TPS ?

TPS is good.

Any other ideas?

no ALDL? no codes?

The only other thing I can possibly think of in your case is a clogged fuel return line. But that's a bad guess because I think the injectors would still blow the air out and still open up and deliver fuel, even if the clogged line would cause a big surge in rpm every time the throttle was cracked.

There should be a constant 12 volts to each injector plug with the ignition turned on. The second wire to the injector is the ground, provided by the computer through the quad driver circuits. Check the injector plugs with a test light (one of the few places that tool is appropriate!) to see if the circuit can flow enough current to light up the bulb, then check for continuity all the way from the injector plug to the computer on the ground side. By momentarily grounding the return wire, the injector shouls squirt. Don't leave the wire grounded for longer than just a quick tap, as the injector windings won't stand a continuous circuit without burning out. If all that checks out OK, try swapping a known good computer into the circuit.
Jerry

Oil pressure sending unit will keep injectors from working.

Ditto on the oil pressure sending unit. GM failsafe if there is no oil pressure at the switch, engine wont run, fuel pump wont pump. There should be a 3-wire switch. One wire for the idiot lamp, the other two tell the ECM there is oil pressure

Scott

be slightly careful with assuming the oil pressure sender switch is bad. i had an 87 that had one go out but it was set up to give the engine fuel for something like 10sec then shut down when it didnt read oil pressure. if your not getting and fuel even on start up it may not be the oil pressure sender (just my $.02) from what i have seen of these type issues at work i think jerry (hotrod) is on the right track

There's a 2-second fuel pump run programmed in when the ignition switch is turned on, plus a constant-run pump mode while the starter is cranking. The oil pressure switch is rollover protection to shut the pump off if the car loses oil pressure. If the engine starts, runs a few seconds, then quits, then check out the oil pressure switch.
Jerry