1990 gm throttle body

[myko]

Have a 1990 chevy silverado. throttle body injectors are not spraying. Sometimes I can start up the truck and it runs good. Then the injectors quit after a few minutes. Sometimes I can start it up again and other times the injectors just won't spray at all. Is there a relay or solinoid that is turning them off or what? Open to any ideas as to get this truck running again. I never know if or when it will run. Thanks.

 

[383 240z]

are the injectors faulty, or is the signal firing them intermitant? Do you have a noid light to test the wiring? Keith

 

[38Chevy454]

Fuel pressure? Fuel pump even operating?

 

[KustomZ]

Sounds like your ECM is going bad. My 95 Chevy 350 TBI did the same thing and that is what had to be replaced.

 

[DiscoBerry]

I would check fuel pressure if thats ok then the pickup coil and ignition module in the distributor

 

[VENNOM]

<---- seconds what disco said, the computor refrences the ign module for ignition and the fuel. If you have spark, and no fuel. that's annother problem

 

[I can fix anything]

I would check fuel pressure if thats ok then the pickup coil and ignition module in the distributor

Fuel pressure is a possibility. Disconnect the return line at the throttle body and check for plenty of volume.

 

[csp]

Fuel pressure is a possibility. Disconnect the return line at the throttle body and check for plenty of volume.

How much is your definition of plenty?

Autozone has loaner fuel pressure testers. Pressure test on the supply and return line will tell more than trying to eyeball fuel in the return line and deciding if it's plenty or not.

I'm with Disco's recommendation. Good fuel pressure means the pickup or ignition module are bad. Ignition modules are relatively inexpensive. I keep an extra just in case.

 

[I can fix anything]

We get a bunch that will have zero flow from the return line yet pressure is in spec.

 

[Lugnut64052]

The spec is 9 to 13 pounds of fuel pressure, but it's been my experience that you need to see 13 or close to it or the truck won't run right. Even then you might have a fuel flow problem.

Next time it dies see if it'll start and run while spritzing the throttle body with a can of starting fluid. We used to drive vehicles into the shop that way, with someone riding on the fender spraying the throttle body to keep it running.

If it won't start on starting fluid, you have an ignition problem.

 

[srmofo]

Like mentioned earlier those old early ecus dont have the greatest track record. Ive replaced 1 on my own 87 TBI....twice. Stupid rebuilt junk. Another sign for a bad ecu is no CEL illumination when keyed on.

Always check the basics mentioned above (spark,fuel pressure, etc) before condemning the ecu. good news is, they're cheap.

 

[chrisziem]

Check the ECM connetions for wiggle and damage to wiring harness. Any crimped connector should be replaced with soldered connections.

 

[ddawg16]

The injectors are fed by their own fuse....with the ign on but not running....make sure there is 12v at the wires....the ECM actually grounds one end of the wire to fire the enjector.

I would be looking at computer codes before I did anything else.

Can you hear the fuel pump start and run for 2 seconds when you first turn on the ign?

My first vote is going to be the fuel pump....then intermittent wire connections....an ECU problem is usually pretty consistant....

 

[adam728]

I vote the module in the distributor. Obviously it can be many things, and you need to check them all. But my two experiences with intermittent fuel issues on tbi Chevys were both caused by that dang module. I keep a known good used spare in my 92 after the headaches we went thru on a friends 89.

 

[930dreamer]

I've replaced two ignition modules over the years in our 91 Burb. It would crank and fire for a few second and die, no intermittent running though.

 

[rodm1]

Tagged

 

[79firebird]

Im thinking ignition module ive had 3 buddys with that year gmc and same prob.

 

[Lotek]

First suspect is the ignition module and pickup, check for evidence of corrosion or rust on the pickup. If you briefly ground the injectors you can check spray pattern, but the injectors are pretty trouble free. I have seen ecm failures and some remans are ****, but ign faults are the primary suspect.