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1991 S10 fuel pump issue please help
02-17-2014, 01:01 PM (This post was last modified: 02-17-2014 01:19 PM by ericbohn1972.)
Post: #1
1991 S10 fuel pump issue please help
I have a 91 S10. I jump started my daughter's car and the truck went dead as soon as turned the key in her car. At first I thought the fuel went because I was not getting any fuel at the throttle body. So I checked the fuses and ended up replacing the fuel pump and relay. This did not fix my problem. While checking things I discovered my injectors did not have any power. I replaced the computer and now the injectors have power but the fuel pump still doesn't work. I then decided to replace the ignition module and that did not help either. I have a constant 8.5 volts going to the fuel pump with the key on. The pump will run if I run a jumper wire straight from the battery. I am scratching my trying to figure this out. Then yesterday I discovered my headlights are not working. All fuses are good and I cleaned the battery ground on both ends along with the headlight ground. Does anybody have an idea what i should check next? Any idea will be helpful. I also replace the alternator because I had it tested and it showed it had a bad regulator.
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02-17-2014, 11:16 PM
Post: #2
RE: 1991 S10 fuel pump issue please help
8.5 volts is not enough to run anything. At that age I suspect poor connections. I would start with a fully charged battery then go to cleaning all cable ends, especially the ground end from the battery to the radiator support. (common issue on a 4.3) Next look at the ground wire that's on the stud at the t-stat housing. If that's not clean it will not start. There's also a ground breaking out of the wiring harness going back to the fuel tank. It goes to a screw on the frame rail near the tank. If all else fails see what the voltage is at the battery. Should be 12.6 or slightly higher. There should be no more than a half volt drop anywhere in the system. If it's more then you need to do some detective work.

Some years had several fuses for the system marked ECM1, ECM2, and fuel pump. They all need to be good!

BTW, that ground on the radiator support is also for the headlights and there may be a second one on the other side of the radiator. On some there's yet another ground on the firewall near the heater case. It's too long ago to say exactly what years / model had that. As I recall, if it goes bad the blower motor also doesn't work. Old vehicles and poor connections go hand in hand.

Let us know what you find.
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