No fuel to TBI

Sounds very similar to the issues I am having with my truck.
Take a look at this post:

https://www.2carpros.com/forum/1992-chevy-truck-chevy-43-no-start-no-fuel-vt191543.html

Here are some wiring diagrams they gave me (below):

Please let us know what happens.

Cheers,

I will check the fuel pump today, but even if it would have worked after I forced the fuel pump relay to activate, my thoughts are that the ECM would not have fired the injectors as it does not send voltage to the fuel relay coil winding and something seems to be telling the ECM to stay shut down like an emergency fuel cut-off switch. I cannot find one in the chassis electrical diagram though. Wished I had a detailed schematic diagram of the ECM as it would help in figuring out what is broke.
Thanks for the response.

Is the service engine soon light on? Try grounding terminal "G" on the test connector, this should power the fuel pump, this is just to test it, do not drive like this! Read the codes while your at it!

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

Cross these two terminals as shown, then turn the key on. Count the flashes, a twenty two will flash as two flashes then a short pause, then two flashes, if more than one code is stored, the pause will be longer. The codes will display three times and end with twelve. Write them down and post here. This connector is right under the middle of the dash.

Merlin2021, I did not try grounding the G connector to see if the fuel pump ran. I had originally run the diagnostics and there were no error codes but failed to add that to my post. I did read code twelve for about ten cycles with no other codes showing.
I measured the fuel pump resistance from the connector that feeds the pump on the gray wire to ground and it is opened. I measured to the ground lug to make sure and also stuck a sewing pin into the wire a few inches from the lug and measured to chassis with zero ohms and did the same on the gray wire to the connector to rule out the connector. I am in the process of removing the bed to replace the pump. I still do not understand why the ECM does not power the fuel relay. I will replace the fuel pump and screen, have replaced the inline filter and will continue from there. Will ground the G terminal afterwards if it still does not function. Will let you know the results. Thank you.

Merlin2021, I grounded the G contact at the test connector and the fuel relay would activate when the ignition switch was turned on. I removed the ground from the G contact and turned on the ignition switch and the fuel relay came on but only for about two seconds. Turning the ignition switch on again did nothing. I then replaced the fuel pump, grounded the G terminal for a few seconds, heard the fuel pump work, removed the ground and heard the fuel pump turn off and then started the engine.

Now that this is fixed, the ECM has to be reading a fuel pressure sensor. Can you tell me where this is or how the ECM knows there is fuel? Hopefully this will never be an issue but would be nice to know.

I appreciate the quick response you gave as I was able to fix my truck before the new work week. Thank you.

Fuel module (7.4L, 5.7L G Van & 5.7L Over 8500 GVWR).
Fuel module overrides the ECM two second timer and fuel pump runs twenty seconds before shutting off when vehicle is not started. This added circuit corrects hot restart problems which could cause vapor lock during high ambient temperatures.

Fuel pump:

An in-tank electric fuel pump delivers fuel to injector(s) through an in-line fuel filter. The pump is designed to supply fuel pressure in excess of vehicle requirements. The pressure relief valve in the fuel pump controls maximum fuel pump pressure.
On TBI fuel systems, pressure regulator is mounted on throttle body. On port fuel injection (PFI) systems, pressure regulator is mounted on the fuel rail. Regulator keeps fuel available to injector(s) at a constant pressure. Excess fuel is returned to fuel tank through pressure regulator return line.

When ignition switch is turned to "on" position, ECM turns on electric fuel pump by energizing fuel pump relay. ECM keeps pump on if engine is running or cranking (ECM is receiving reference pulses from ignition module). If there are no reference pulses and vehicle is not equipped with a fuel module, ECM turns pump off within two seconds after ignition is turned on. For additional information, see Fuel pump relay and Fuel module under fuel delivery.

Fuel pressure regulator (CPI):
A constant fuel pressure of 54-64 psi (3.8-4.5 kg/cm2 ) is maintained by a factory preset, nonadjustable, spring loaded diaphragm contained within CPI assembly. Spring tension maintains a constant fuel pressure to injector regardless of engine load.

Fuel Pressure Regulator (TBI):
A constant fuel pressure of 9-13 psi (.6-9 kg/cm2 ) is maintained by a factory preset, nonadjustable, spring loaded diaphragm contained within throttle body. Spring tension maintains a constant fuel pressure to injector regardless of engine load.

Fuel Pressure Regulator (4.3L Turbo PFI)
Fuel pressure regulator is a diaphragm-operated relief valve with injector pressure on one side and manifold pressure (vacuum) on the other. Pressure regulator compensates for engine load by increasing fuel pressure when low manifold vacuum is experienced.
During periods of high manifold vacuum, regulator-to-fuel tank return orifice is fully open, keeping fuel


pressure on the low side of its regulated range. As throttle valve opens, vacuum to regulator diaphragm decreases, allowing spring tension to gradually close off return passage. At wide open throttle (when vacuum is at its lowest), return orifice is restricted, providing maximum fuel volume and maintaining constant fuel pressure to injectors.

Fuel pump relay:
When ignition switch is turned to ON position, ECM turns electric fuel pump on by energizing fuel pump relay. ECM keeps relay energized if engine is running or cranking (ECM is receiving reference pulses from ignition module). If there are no reference pulses, ECM turns pump off within two seconds after key on.


As a back-up system to fuel pump relay, the oil pressure switch also activates fuel pump. The oil pressure switch is normally open until oil pressure reaches approximately four psi (.28 kg/cm 2 ). If fuel pump relay fails, the oil pressure switch closes when oil pressure is obtained, and operates the fuel pump. An inoperative fuel pump relay may result in extended cranking times due to the time required to build up oil pressure. Oil pressure switch may be combined into a single unit with an oil pressure gauge sending unit or sensor.

ECM monitors fuel pump circuit between fuel pump relay/oil pressure switch and fuel pump, enabling ECM to determine if fuel pump is being energized by fuel pump relay or oil pressure switch. A failure in this monitored circuit results in the setting of a related trouble code in ECM memory.

I am having the same problem, sometimes it does not start, but starting fluid gets it started for two seconds. Checked for all good grounds, and changed the starter wire. I am hearing the fuel pump come on, checked the lines- pumps good psi, and i am hearing the relay "click" on. this morning it starts but only with one injector running twice as hard. after driving for thirty minutes the other kicks on and it runs perfect the rest of the day, so long as i do not turn it off for too long. a friend also mentioned cold weather having an impact, but not with fuel, right? i am going to get a noid light, any help would be great.

I am going to have to try that "G" ground process on terminal. If I cannot fix my "no start" problem today. I am going to post what my findings are in my application. Some of the different posts on here are almost identical, but they never get resolved or the owner never responds after they get it fixed!

Alright, I have a question for you guys, I have a 1993 Chevrolet C3500. It had a 5.7 but I turned it into a 383 Stroker carburetor with a HEI vacuum advanced MSD distributor. It will start and run for about twenty to thirty seconds before the fuel pump kicks off. I assume it is because the ECM is not receiving signal from the Ignition control module or somewhere along those lines. Is there a way to bypass this? Or do I just have to run a positive lead from the fuel pump to a toggle? I have a pressure regulator with a return running from the fuel lines so I am getting correct pressure I just cannot keep the fuel pump running.

Well nine times out of ten with the 4.3 pick up coil in the base of distributor, will cause no fuel from injectors. Ignition module is other component that will cause crank no start after is be warm for short amount of time. Then if you let set and cool down, will fire off again.

Alright guys I have one for you! I have a 1992 gmc serria z71 with the 5.7 tbi. It will start for about five minutes then die and won’t fire back up for a couple hours then do the same thing over again. I’ve replaced the fuel pump relay the fuel pump the oil pressure sensor the water pump the thermostat the temp sensor and replaced the carb with a different one and the pcm. Thought it might have had a massive intake leak so I went ahead and did that as well. Any thoughts? After all that it still only runs for five minutes or so then turns off and will not fire back up. It’s driving me nuts I can’t figure it out!!!

When it shuts down do you still have spark? You can check out this guide to see how to test it so we can go from there. Sorry about the delay.

https://www.2carpros.com/articles/how-to-test-an-ignition-system

Please let us know what you find. We are interested to see what it is.

Cheers, Ken