91 GMC 2500 died, fuel in the feed line, not getting to injectors

[Jwill000]

I have a 91 GMC 2500, 5.7L. was jumping our dump truck a few weeks ago and it just died, I figured maybe it ran out of gas - but it didn't . I knew the fuel pump was on it's way out(hard to start in winter) so I replaced with a 96+ fuel pump, tossed on new filter and relay, fuse good. I'm getting high volume at the feed line at the throttlebody(cannot find a schrader valve to test pressure). I couldn't get the return line loose at the throttle body, will keep fighting with it when weather permits.

I don't have a noid light for the injectors, I can't tell if they're firing during cranking

the truck will run off starting fluid so the spark is working

the injectors have a good 12v signal with key on - again, unable to test ground while cranking

both injectors will fire with a 9v battery but no gas comes out

the temp sensor is like 2 weeks old

I'm thinking, either a blockage in the throttle body casting(is that common?) or I read somewhere the ecu might not be getting the right signal from the distributer and I could run a new line from the dizzy to the ecu(wherever that is). not sure if that's worth looking into or not

truck's been rock solid for years - now I'm lost

 

[89obsSB]

I’d start with checking fuel pressure. You’ll need adapters and what not since the tbi setups don’t have a Schrader valve.

 

[Schurkey]

I have a 91 GMC 2500, 5.7L. was jumping our dump truck a few weeks ago and it just died, I figured maybe it ran out of gas - but it didn't . I knew the fuel pump was on it's way out(hard to start in winter) so I replaced with a 96+ fuel pump, tossed on new filter and relay, fuse good. I'm getting high volume at the feed line at the throttlebody(cannot find a schrader valve to test pressure).

High volume is a good sign, but not a substitute for testing fuel pressure. As said, the TBIs don't have service fittings. You'll have to add an adapter/service fitting to test pressure.

The two kinds I know about are a metal block that takes the place of a fuel filter, and has a Schrader valve on it; the other is an adapter that goes between fuel supply tube and the throttle body, and has a Schrader valve on it. Make sure your pressure adapter has the same style of service fitting as your fuel pressure tester. There's at least two sizes of Schrader valves, and OTC uses a goofy quick-connector.

I don't have a noid light for the injectors, I can't tell if they're firing during cranking

Would be worth getting a 'noid light suitable for TBI; or an LED test light that does about the same thing. A regular incandescent test light is not going to work.

the truck will run off starting fluid so the spark is working

Which also verifies the pickup coil in the distributor, and most but not all of the ignition module.

the injectors have a good 12v signal with key on - again, unable to test ground while cranking

It's the ground that's the crucial part. The ECM grounds the injectors to fire them.

both injectors will fire with a 9v battery but no gas comes out

First Guess: Because the fuel pump is not running, therefore no fuel pressure, therefore no fuel spray from the injector.

I'm thinking, either a blockage in the throttle body casting(is that common?)

No.

or I read somewhere the ecu might not be getting the right signal from the distributer and I could run a new line from the dizzy to the ecu(wherever that is). not sure if that's worth looking into or not

Connect a scan tool to the ALDL. Look for an RPM signal when cranking. If you have an RPM reading, the ignition module and the RPM signal wire to the ECM is fine. If you DON'T have an RPM reading when cranking, that's probably the problem. Could be failed module, could be failed wire/wire connectors.

 

[Jwill000]

Connect a scan tool to the ALDL. Look for an RPM signal when cranking. If you have an RPM reading, the ignition module and the RPM signal wire to the ECM is fine. If you DON'T have an RPM reading when cranking, that's probably the problem. Could be failed module, could be failed wire/wire connectors.

the OBD1 port has never worked

guess I'm ordering a noid light and checking some other things

 

[89obsSB]

the OBD1 port has never worked

guess I'm ordering a noid light and checking some other things

Not sure about obd1 connectors. But the obd2 connectors will loose power if the cig lighter fuse is blown.

 

[Schurkey]

FIX the ALDL/OBD1 port.

 

[Jwill000]

FIX the ALDL/OBD1 port.

I'm guessing it won't tell me crap from my experience with no start obd1 cars

maybe I'll just toss on a carb mechanical dist rather than chasing my tail with this if the noid light and $50 schrader valve thing doesn't pan out

 

[GoToGuy]

Your chasing your tail, not doing the correct diagnostic. You guessed about a few items but did no trouble shooting.
OBD port not working, how do you expect to do any diagnostics if you can't communicate with your truck?

 

[tayto]

blow compressed air through the supply line to see if it is blocked.

 

[Schurkey]

I'm guessing it won't tell me crap from my experience with no start obd1 cars

It'll tell you whether there's an RPM signal, which divides the problem areas in half, so you can focus on the proper parts.

If the computer has an RPM signal, it should know to fire the injectors. Problem is Computer, or downstream from the computer to the injectors. If the computer does not have an RPM signal, problem is upstream from the computer--distributor or wire harness to the computer.

maybe I'll just toss on a carb mechanical dist rather than chasing my tail with this if the noid light and $50 schrader valve thing doesn't pan out

That'd be a huge mistake.