1993 Chevrolet Truck



October, 3, 2008 AT 5:18 PM

Electrical problem
1993 Chevy Truck V8 Two Wheel Drive Manual 170000 miles

Truck suddenly would not start this morning. Originally had no fire past distributor. Replaced distributor cap and rotor but not working. Eventually turned distibutor and now have spark at plugs but no fuel. Eventually found no voltage from ECM going to fuel relay on green/wht wire. I applied 12 vdc and activated the relay. Measured 12 vdc on the output gray wire all the way to the fuel pump. Pulled off one of the fuel injector connectors and applied 12 vdc to the injector and it activated but still no fuel. What should the resistance of the fuel pump be? I do not hear it running. Need to know what other sensors if any can cause the ECM to not power this relay and am concerned that there is something else that the ECM is seeing to cause both the spark and fuel problems. Presently I can pour gasoline in the carburator and the engine wants to start so it's a fuel issue at this time. Any suggestions would be appreciated.
Forgot to add that there were no code faults registered.


10 Answers



October, 3, 2008 AT 8:36 PM

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

I will be watching for resolution for your problem
Good luck



October, 4, 2008 AT 6:53 AM

Soonerbills - 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 can't 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.



October, 5, 2008 AT 10:46 AM

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!

Cross these two terminals as shown, then turn the key on. Count the flashes, a 22 will flash as 2 flashes then a short pause, then 2 flashes, if more than one code is stored, the pause will be longer. The codes will display three times and end with 12. Write them down and post here. This connector is right under the middle of the dash...



October, 5, 2008 AT 11:48 AM

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 12 for about 10 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 0 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 don'd 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.



October, 5, 2008 AT 10:02 PM

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 2 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.



October, 6, 2008 AT 2:29 PM

Fuel Module (7.4L, 5.7L G Van & 5.7L Over 8500 GVWR)
Fuel module overrides the ECM 2-second timer and fuel pump runs 20 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 2 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 2 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 4 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.



December, 16, 2008 AT 8:38 AM

Im having the same problem, sometimes it doesnt start, but starting fluid gets it started for 2 seconds. Checked for all good grounds, and changed the starter wire. Im hearing the fuel pump come on, checked the lines- pumps good psi, and im hearing the relay " click" on. This morning it starts but only with one injector running twice as hard. After driving for 30 minutes the other kicks on and it runs perfect the rest of the day, so long as I dont turn it off for too long. A friend also mentioned cold weather having an impact, but not with fuel, right? Im going to get a noid light, any help would be great.



May, 27, 2009 AT 5:10 AM

I'm going to have to try that " g" ground process on terminal. IF I can't 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 respnds AFTER they get it foxed!



January, 18, 2014 AT 2:55 PM

Alright I had a question for you guys, I got a 1993 Chevrolet C3500. It had a 5.7 but I turned it into a 383 stroker carbureted with a HEI Vacuum advanced MSD Distributor. It will start and run for about 20-30 seconds before the fuel pump kicks off, I assume it's 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'm getting correct pressure I just can't keep the fuel pump running.



September, 7, 2014 AT 2:45 PM

Well nine times out of ten with the 4.3 pick up coil in the base of distbutor, cause no fuel from injectors. Ingnition 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.

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