1991 S-10 4x4 4.3 L Fuel Pump Blows Fuse

Ok, here is the issue, I replaced the fuel pump, checked the wiring between the fuel pump and the relay and it all checks out fine.

However, when connecting power to the fuse box, with a fuse, the fuse blows instantly.

I pulled the fuse box out, check everything, and it still blows the fuse.

Is it the computer? I checked every wire except the orange one from the fuse box to the relay, which is covered, and looks not to be grounding out and causing the fuse to blow.

The relay is new, it works, checked it with a meter and the fuel pump is new ( tested it getting 12.6 V to it and it pumps.)

Any help would be great.

Ok, here is the issue, I replaced the fuel pump, checked the wiring between the fuel pump and the relay and it all checks out fine.

However, when connecting power to the fuse box, with a fuse, the fuse blows instantly.

I pulled the fuse box out, check everything, and it still blows the fuse.

Is it the computer? I checked every wire except the orange one from the fuse box to the relay, which is covered, and looks not to be grounding out and causing the fuse to blow.

The relay is new, it works, checked it with a meter and the fuel pump is new ( tested it getting 12.6 V to it and it pumps.)

Any help would be great.

ok the orange wire from the fuse box is from 'ecmb' and is 10A, it goes to a junction where it splits and feeds the ECM twice, sends orange to the oil pressure switch on the back of the motor and sends oragne to the fuel pump relay.

now trace the back end of the relay for a gray or tan w/whit that joins with the same colors from the fuel pump prime and the same colors from the oil pressure switch output and heads to the tan wire at the pump.

so here is what you need to do....probe the gray or tan/white wire with a light connected to +12v and look for a light - WITH the fuel pump unplugged - that looks for a short. then probe the tan pump wire to ground and look for resistance, since the amperage is 10A and some of this goes to the ECM, lets assume 8 is for the pump, you should have at least 1.5 ohms for the pump - prolly closer to 3. you are blowing a 10A fuse quickly, meaning it is seeing at least a 15A initial.

as another test, unplug the oil pressure switch and try again. it will start and run and shut off normally.

however, key off, the fuse is not energized, from your post you are saying it is, is this true?

This is what I did,

I see the ECM - B with the 10A fuse. Back near the pump I have continuity in the wiring from the Purple and Grey wires back to the pump. ( meaning it does not short out on my meter )

The left side of the fuse ( orange wire ) is cold, the right is hot when the ignition is on.

Now, when I put a fuse in, it fires off, even at a 30A ( which I know I should not do, but did anyways) It fires off, with the ignition switch on.

Now, the Orange wire, I am assuming goes to the relay, or the computer? And then loops back to the fuse box.

Not sure about the oil pressure switch? Is that near the back of the motor, and I am assuming that your saying that the split goes to that AND the relay? Does the computer get in this mix? as I am worried the computer is fried, or maybe now that your saying this the Oil pressure orange wires, may have a ground fault on this some how.

Again, I have isolated it from the fuse box to the relay. The gray and purple wires going to the Fuel pump are fine. It is now between the Fuse box and whatever the split is from that ( NOT THE RELAY )

Thanks again for your response!

Paul

Ok, on the back of the motor, up top to the right of the dist as you face it, its the oil pressure switch. IT has 3 wires, in/out and oil pressure sense, unplug this and that will eliminate the switch being shorted to ground.

Ok, on the back of the motor, up top to the right of the dist as you face it, its the oil pressure switch. IT has 3 wires, in/out and oil pressure sense, unplug this and that will eliminate the switch being shorted to ground.


Ok, if I unhook this, and it does not short, would I assume that the grounding is happening between the Fuse Box and the Oil Pressure switch?

If this is true, would you also assume that the Oil Pressure switch is shot if I cannot find the ground fault in the wiring?

Thank you so much, your a great help!

Paul

If you pull the wires to the switch, and it now works fine, then yes, the switch is bad

If you pull the wires to the switch, and it now works fine, then yes, the switch is bad


Cool, I will try that and see if the pressure switch is toast. Hopefully that is it, what a pain in the rear starting from the Fuel pump and then finding out it is the darn Oil Pressure switch. Bummer.

Thanks again!

Paul

Cool, I will try that and see if the pressure switch is toast. Hopefully that is it, what a pain in the rear starting from the Fuel pump and then finding out it is the darn Oil Pressure switch. Bummer.

Thanks again!

Paul


Ok, got that part fixed, now I have no spark from the solonoid, it is getting power to the solonoid, but no power from out of the solonoid to the distributor.

Also, the Tubs are not spraying fuel down the TB, It is pumping gas like crazy ( unhooked fuel line and let me tell you , it pumps it out like mad )

Trying the solonoid in the morning, if that is not it, craps.

Paul

Replaced the ICM and the Coil and I get spark.

I tested the Fuel Injector wires, they are getting like 12.3 volts, but the fuel is not coming out.

i took the TB off and cleaned them all out and still nothing.

Do they go to crap sitting for about a year?

Looks like I may have to replace those Fuel Injectors?


Thanks again!

Ok, here is the issue, I replaced the fuel pump, checked the wiring between the fuel pump and the relay and it all checks out fine.

However, when connecting power to the fuse box, with a fuse, the fuse blows instantly.

I pulled the fuse box out, check everything, and it still blows the fuse.

Is it the computer? I checked every wire except the orange one from the fuse box to the relay, which is covered, and looks not to be grounding out and causing the fuse to blow.

The relay is new, it works, checked it with a meter and the fuel pump is new ( tested it getting 12.6 V to it and it pumps.)

Any help would be great. Under the carpet in front of the the extreme right pedal are three groups of wires put into one harness, if you check these wires one at a time I think you will find the fuse blower.
It's metal on the bottom and your foot is constantly wearing these out . I formed a small piece of raised metal siliconed them in and so far so good. before I was asking the same thing you are. Hope it helps.

I found that, however, it was the Oil Pressure switch that was blowing the fuse.

Now, I am not getting a Pulse to the Fuel Injectors and I think that the ECM ( Computer ) maybe bad.

Any suggestions?


Thanks!

Paul

I found that, however, it was the Oil Pressure switch that was blowing the fuse.

Now, I am not getting a Pulse to the Fuel Injectors and I think that the ECM ( Computer ) maybe bad.

Any suggestions?


Thanks!

Paul

are you getting spark flash? the ign system triggers the ecm which triggers the inejectors, look again in the fuse box and make sure all ecm fuses and ones labelled 'ign' are not blown

I am getting spark to the system.

I replaced the Coil, the ICM also.

I dumped fuel into the throtlle and it fired up.

However, the injectors are not firing fuel in the TB.

I triple checked the fuses and they are all fine and in the proper places.

What else could it be? ( did you hear that? I am thumping my head on the fender of the truck!!!)

:)

Thanks again dude!

Paul

I am getting spark to the system.

I replaced the Coil, the ICM also.

I dumped fuel into the throtlle and it fired up.

However, the injectors are not firing fuel in the TB.

I triple checked the fuses and they are all fine and in the proper places.

What else could it be? ( did you hear that? I am thumping my head on the fender of the truck!!!)

:)

Thanks again dude!

Paul

I am getting power to the injectors, but it seems not to "pulse" as the auto-parts people are telling me. They seem to know crap about what it is.

I checked it with a light, I am getting 12.9 V, and it cranks, but no pulse to the injectors.

Paul

no signal with noid light replace ecm faulty