Not starting

hello all;
I have a project 1991 Chevrolet C1500 with a 5.0L engine with a TBI on top. The truck started and ran last year. Now that I have the truck ready to come out of the shop, I can not get her to start. Apparently the fuel pump is not turning on. (the pump is brand new, and when I by-pass the fuel pump relay I can hear the pump run.) Also the injectors are not injecting fuel. IfI pour a little fuel into the TBI the truck will start and run,until the fuel is all used. Im at the end of my wits. I have replaced the ignition module, and still not starting.

those trucks wont start if below sea level.

or, easiest quicky check, jump wire to fuel pump so it runs constantly, if still doesnt start, replace ICM. it is a maintenance item, and fails on a regular basis. if those dont work, then you needed an ICM anyway, and now you know your pump will pump! time to devote some trubleshooting after that.

oh, and sitting on top of wood shavings that low, will be a perfect place for those little wire eaters we call RATS

Redneckgeriatric said:

those trucks wont start if below sea level.

or, easiest quicky check, jump wire to fuel pump so it runs constantly, if still doesnt start, replace ICM. it is a maintenance item, and fails on a regular basis. if those dont work, then you needed an ICM anyway, and now you know your pump will pump! time to devote some trubleshooting after that.

oh, and sitting on top of wood shavings that low, will be a perfect place for those little wire eaters we call RATS

Click to expand...

Replaced the ICM yesterday. Going through all the wiring coming off of the PCM

FIRST,, this may sound dumb, but are you SURE the truck has gas in it? if it sat a year, did u drain the fuel? if not did u add stabil? u may have jello in the tank.

when u bypass the relay, does it start and run without adding fuel? if not, unplug one of the connectors going to the tbi and put a voltmeter in the plug and see if u get 12 volts DC to the plug when cranking,, if not, u arent getting a signal from the computer.

When I by-pass the relay it still wont start,because the injectors are not injecting. I put fresh fuel in the tank within two weeks ago. I put a tester on all four leads on the injector. With the key on 1 wire per injector gets power. When the key is turned the other wire does nothing. Which tells me no pulse to the injectors. Plus I wasn't getting any reading from the wire that goes from the ECM to the fuel pump relay when the truck tries to start. I wish there was a way to really test the ECM.

Also not getting a check engine light when I turn the ignition on. No light when I do a "No OBD1" checking device test.

Channeled 91 said:

With the key on 1 wire per injector gets power. When the key is turned the other wire does nothing.

Click to expand...

The injectors get 12vdc when key is on/cranking/running, when you're cranking/running the other leads should be grounded intermittently as the ECM calls for fuel.

PlayingWithTBI said:

The injectors get 12vdc when key is on/cranking/running, when you're cranking/running the other leads should be grounded intermittently as the ECM calls for fuel.

Click to expand...

I took a wire from the hot wire on one injector and ran it to the "intermediate ground wire and had the truck turn over. The test Light should have pulsated on and off, but it did nothing.

Channeled 91 said:

I put a tester

Click to expand...

WHAT KIND of "tester"?

Channeled 91 said:

on all four leads on the injector. With the key on 1 wire per injector gets power. When the key is turned the other wire does nothing. Which tells me no pulse to the injectors.

Click to expand...

As said...one wire is "hot", the other is grounded by the ECM intermittently to cause the injector to pulse/spray.

A 'Noid light connected to the injector harness should flash when the engine is cranking.

The injectors may be varnished-shut. I installed a Treasure Yard TBI assembly on my truck. When I started the engine, four cylinders didn't run, it idled like crap. One injector didn't spray fuel at all. I swapped connectors between the two injectors, but the same injector still didn't spray. I was getting ready to put the original TBI back on, and "poof" the second injector starts spraying, and has been fine for tens of thousands of miles since then.

Channeled 91 said:

Plus I wasn't getting any reading from the wire that goes from the ECM to the fuel pump relay when the truck tries to start. I wish there was a way to really test the ECM.

Click to expand...

Do I have this right? The ECM won't turn on the fuel pump relay, not to prime when the key is turned "on", and not when the engine is cranking.

The injectors never spray fuel.

The engine has spark, and it'll run if you manually drop fuel down the throttle body.

I'd be looking for a wiring fault between the distributor and the ECM; and between the ECM and the fuel pump relay control circuit; and on the power-supply side of the fuel pump relay including the fuel pump fuse.

Channeled 91 said:

Also not getting a check engine light when I turn the ignition on. No light when I do a "No OBD1" checking device test.

Click to expand...

No Check Engine light can signify a defective ECM. Could also be a problem in the wire harness, or even the light-bulb is burned out. Have you verified the ECM fuse?

Channeled 91 said:

I took a wire from the hot wire on one injector and ran it to the "intermediate ground wire and had the truck turn over. The test Light should have pulsated on and off, but it did nothing.

Click to expand...

I have no idea what you're trying to say. The injectors have power all the time. The control of the injectors is done on the ground side of the circuit. So a test light connected to the power wire isn't going to flash unless the test light is grounded through the injector ground wire. Which is the whole point of a Noid light. A test light connected to injector power and ground should be "on" whenever the ignition is "on".

Schurkey said:

WHAT KIND of "tester"?


As said...one wire is "hot", the other is grounded by the ECM intermittently to cause the injector to pulse/spray.

A 'Noid light connected to the injector harness should flash when the engine is cranking.

The injectors may be varnished-shut. I installed a Treasure Yard TBI assembly on my truck. When I started the engine, four cylinders didn't run, it idled like crap. One injector didn't spray fuel at all. I swapped connectors between the two injectors, but the same injector still didn't spray. I was getting ready to put the original TBI back on, and "poof" the second injector starts spraying, and has been fine for tens of thousands of miles since then.


Do I have this right? The ECM won't turn on the fuel pump relay, not to prime when the key is turned "on", and not when the engine is cranking.

The injectors never spray fuel.

The engine has spark, and it'll run if you manually drop fuel down the throttle body.

I'd be looking for a wiring fault between the distributor and the ECM; and between the ECM and the fuel pump relay control circuit; and on the power-supply side of the fuel pump relay including the fuel pump fuse.


No Check Engine light can signify a defective ECM. Could also be a problem in the wire harness, or even the light-bulb is burned out. Have you verified the ECM fuse?


I have no idea what you're trying to say. The injectors have power all the time. The control of the injectors is done on the ground side of the circuit. So a test light connected to the power wire isn't going to flash unless the test light is grounded through the injector ground wire. Which is the whole point of a Noid light. A test light connected to injector power and ground should be "on" whenever the ignition is "on".

Click to expand...

I have untaped and checked all the wires in the engine bay and under the dash. They all seam fine. The fuel pump fuse is good.