1992 Chevy Truck truck suddenly stopped running

craig dean · Posted at Thu Oct 29, 2009 1:38 pm

Electrical problem
1992 Chevy Truck V8 Two Wheel Drive Automatic

My 1992 3/4 ton with 7.4L suddenly stopped running. There was no warning such as hesitation when fuel is low. I removed the air cleaner top and poured fuel into the throttle body and attempted to start it and it started until the fuel ran out. That eliminated any ignition problems. Now i started to look into the fuel system. I removed the fuel pump from the tank and tested it on the bench and it works. I checked the ECM fuses they are OK. The fuel pump fuse and relay are OK also. I replaced the engine control computer and it still does not start. I loosened the fuel line fitting on the back of the throttle body and turned the engine over and no fuel is getting to the inlet. I have replaced the fuel pump and fuel filter also. What else can I test or check to determine what is wrong?

merlin2021 · Posted at Thu Oct 29, 2009 10:44 pm

Fuel Pump Oil Pressure Switch (Back-Up Circuit) To test fuel pump oil pressure switch back-up circuit, start engine. With engine running, disconnect fuel pump relay. If engine stalls, fuel pump oil pressure switch is faulty. If vehicle continues to run, switch is okay. Fuel Pump Relay See RELAYS, SOLENOIDS, MOTORS & MODULES. Fuel Pump Relay By-Pass Procedure If fuel pump will not energize, relay may be by-passed to test fuel pump. Turn ignition off. Using a fused jumper wire, apply battery voltage to fuel pump test connector. Fuel pump should turn on. For fuel pump test connector location, refer to COMPONENT LOCATIONS .

After you bypass the relay, check for power at the fuel pump connector. If I remember, it's a gray wire for power. If no power, follow the wire to the inline fuse...check that.

craig dean · Posted at Fri Oct 30, 2009 5:23 pm

I replaced the Fuel pump relay, fuel pump still does not run. I checked the power to the fuel pump fuse at the under hood location and found that both terminals of the fuse holder are grounded. Also there is no continuity between the fuse and the fuel pump relay. Where does the power come from that goes to the fuel pump fuse? and why would both terminals be grounded. That fuse should have 12 volts on it at all times, right? Totally confused.

merlin2021 · Posted at Sat Oct 31, 2009 5:28 am

The Gray power wire is powered by the PCM, and is cut out by low oil pressure switch, try the test connector test that I described above, the connector should be over by the master cylinder.
Fuel Pump Relay 1. If a prolonged crank is required to start vehicle, fuel pump relay may be faulty. To verify this, start engine. With engine running, disconnect oil pressure switch (fuel pump back-up circuit). If engine stalls, fuel pump relay is faulty. If vehicle continues to run, relay is okay. Check for other causes of prolonged crank. 2. To test fuel pump relay, disconnect fuel pump relay. Refer to COMPONENT LOCATIONS. See Fig. 4 . Apply battery voltage and ground to fuel pump relay winding terminals. To identify fuel pump relay terminals, see appropriate WIRING DIAGRAMS article in this section. 3. Using an ohmmeter, check continuity between fuel pump relay power and fuel pump relay drive terminals. Continuity should exist. If continuity does not exist, fuel pump relay is defective. 4. To by-pass fuel pump relay on vehicle (fuel pump not operating), turn ignition off. Disconnect fuel pump relay connector. Using a fused jumper wire, connect fuel pump test connector to positive side of battery. Fuel pump should run. 5. If fuel pump runs, check for faulty connections to relay or replace defective relay. To locate fuel pump test connector, refer to COMPONENT LOCATIONS .

craig dean · Posted at Sat Oct 31, 2009 12:35 pm

I think maybe we are not on the same page here. I mentioned in the first note that the engine will not start. I can not start the engine unless I pour fuel down the throttle body. And then it only runs for a couple of seconds. What i found today was the gray wire that goes to the oil pressure switch was chaffed and grounded against the air cond compressor. I have replaced the following items with new parts.
Fuel pump
Fuel filter
Fuel pump relay
Engine control computer
Oil pressure/fuel pump switch
Can you provide a wire diagram that is specifically for my truck. I am using a Haynes repair manunal that is for 1988 to 1998 and is generic for those model years. I need to know the exact color of the wires that should be on my truck so I can check continuity between components.

craig dean · Posted at Sat Oct 31, 2009 1:55 pm

I found taht the fuel pump relay orange wire goes to a fusable link off of the firewall terminal strip. I check the voltage at the terminal strip, it is 12.5 v. I stuck the meter probe throu the insulation on the other side of the fusable link and only have 6V. Should there be a voltage drop through the fusable link or should I see 12 volts also? I found out that the fuse on the firewall is an in-line fuse after the relay and oil press switch. When I applied power to one side of the fuse holder the fuel pump started. Now I just nee to know if I need to replace the fusable link that applies 12 volts to the orange wire on the relay and oil press switch.

merlin2021 · Posted at Sun Nov 01, 2009 6:15 am

As long as the link test zero ohms with engine off it should be OK the oil pressure switch is what I'm driving at here, but you did say you changed it already, so it may be the ignition switch, or wiring. With 12v applied to the wire that turns on the fuel pump, the truck should start? Now pull out the fuel pump relay and see what happens. Also test that orange wire it's full length. I thought I sent you the wiring diagram already, but I will resend it now!

craig dean · Posted at Sun Nov 01, 2009 6:16 pm

the truck is now running, but now it will not shift out of 2nd gear. I don't think I touched anything that would affect the transmission. Have any ideas?

craig dean · Posted at Mon Nov 02, 2009 3:46 pm

On the fuse block to the left of the steering wheel there is a fuse labeled TRANS. It is a 10 amp fuse and I checked to see if there is power coming to the fuse. There is no power at the fuse with the key in the ON position. I looked at the back of the fuse block and it appears that a 12ga pink wire is going into one side and a small pink wire is on the other side. I need to know where the large pink wire is coming from so I can check if there is a fusable link that has blown. Can you lead me to it?

craig dean · Posted at Mon Nov 02, 2009 9:57 pm

Sure would like a response to my last message.

Regards,
Craig