Fuel pump fuse

[kakanator]

I keep popping the fuse when I am driving and don't know why. When It happens I check the wiring harness that goes to the fuel pump and everything looks good. Then I start checking the part where that harness connects by the driver floor and that looks good. Then It still pops it when I turn the key on and It will only happen when I turn the key to the on position. As in I can put a new fuse in and It wont pop till the key turns. Then after checking stuff for about an hour (by this time I have gone through 9 fuses) I try it one last time then bam car starts. I am glad I had a box of 25 15a fuses can anyone help me? The car is an 87 GE with a bad knock sensor. I don't know if that would be the prob or and the sensor that goes to the tranny for the reverse is broken on the tranny side.

 

[AJ'S 88NA]

Usally when a fuse keeps popping you have a direct short, like a wire with bad insulation is grounding out. I suppose the fuel pump could be bad also but there is a check for that in the TSRM.

 

[kakanator]

That's what I was thinking but I can't find the test on TSRM. Because I have checked all of the wires and even took the fender off today to check that set of wires that goes from the fuse box to the fuse block in the floor board.

 

[AJ'S 88NA]

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=71

 

[hvyman]

Is it the efi fuse?

Easy way to not pop fuse's is to take a head light and wire it in place of the fuse, leave the key in the on position and start messing with wires in that circuit. When the light goes out you've found the circuit.

If it is the efi fuse then there is more to that circuit than just the fuel pump.
I had mine pop many fuses when my o2 wires melted down on the turbo once.

 

[kakanator]

Could it be the fuel pump overheating and popping the fuse for some reason and will not pop it once it cools down? Because that is what I think its doing. After siting for a while the car just starts.

---------- Post added at 06:52 PM ---------- Previous post was at 06:50 PM ----------

Yes EFI fuse its a 15a at the bottom right of the fuse box.

---------- Post added at 06:53 PM ---------- Previous post was at 06:52 PM ----------

Is it the efi fuse?

Easy way to not pop fuse's is to take a head light and wire it in place of the fuse, leave the key in the on position and start messing with wires in that circuit. When the light goes out you've found the circuit.

If it is the efi fuse then there is more to that circuit than just the fuel pump.
I had mine pop many fuses when my o2 wires melted down on the turbo once.

I don't get it. How do I do this?

 

[hvyman]

Take the fuse out, Take a old head light or headlight bulb, Attach a wires to the + side of it and attach a wire to the - side of the prongs and then push some of each wire into seperate parts of where the fuse goes. Dont put part of each wire into both slots that will just short out and melt wires.

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=55
See the efi fuse on that page. See the 2 wires going to it? Everything connected to those wires can blow the efi fuse. Its not just the fuel pump.

Could be the fi main relay, circuit opening relay, fuel pump control relay, fuel pump, fuel pump resister, ign coil, o2 sensor, ecu, etc, etc etc..... There are many components on that circuit other than the fuel pump.

 

[kakanator]

Take the fuse out, Take a old head light or headlight bulb, Attach a wires to the + side of it and attach a wire to the - side of the prongs and then push some of each wire into seperate parts of where the fuse goes. Dont put part of each wire into both slots that will just short out and melt wires.

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=55
See the efi fuse on that page. See the 2 wires going to it? Everything connected to those wires can blow the efi fuse. Its not just the fuel pump.

Could be the fi main relay, circuit opening relay, fuel pump control relay, fuel pump, fuel pump resister, ign coil, o2 sensor, ecu, etc, etc etc..... There are many components on that circuit other than the fuel pump.

Okay if I do the light bulb thing what do I look for? and the wires you are talking about are b-y and b-o that go into the gray box?

 

[hvyman]

You put the light in the place of the fuse so you dont blow the fuse. Like have it there instead of the fuse, ign in the on position, and say pull the efi main relay. The light goes out because you disconnected the circuit and it could be the relay thats your problem or it could be something farther down in the fuel pump circuit.

Just put the light in place of the fuse so your not just replacing fuses non stop and its easier to see if your on the right circuit. If you look at the wiring diagrams and follow the wires you can see everything in that circuit and then the repair manual is also so you can see how to test each component. Like the fuel pump relay is just removing it and then taking a multimeter and check to make sure it has resistance between 2 different prongs and no resistance between another 2 and takes no longer than a man to check.

Btw this is kyle, and elliot saw how i did the light thing.

 

[kakanator]

You put the light in the place of the fuse so you dont blow the fuse. Like have it there instead of the fuse, ign in the on position, and say pull the efi main relay. The light goes out because you disconnected the circuit and it could be the relay thats your problem or it could be something farther down in the fuel pump circuit.

Just put the light in place of the fuse so your not just replacing fuses non stop and its easier to see if your on the right circuit. If you look at the wiring diagrams and follow the wires you can see everything in that circuit and then the repair manual is also so you can see how to test each component. Like the fuel pump relay is just removing it and then taking a multimeter and check to make sure it has resistance between 2 different prongs and no resistance between another 2 and takes no longer than a man to check.

Btw this is kyle, and elliot saw how i did the light thing.

Got it just need to find a lite. I went to the junk yard today and got a different relay and a fuel pump resistor. I there a way to tell if the relay is bad? Like how may ohms or something?

 

[ABNPayne]

Seven years ago I popped one on the interstate southbound in BFE Tennessee. I had been doing 110+ in my 86 Mk2 for quite a while tho, I had it insurance company tow it to the nearest shop 30 miles away... Tow truck driver broke a tie-rod, I ripped him a new one and had him pay the shop. Mechanic said come here Bud, then showed me the blown 10A fuse... Live and learn.

So are you driving 110+?

 

[kakanator]

Seven years ago I popped one on the interstate southbound in BFE Tennessee. I had been doing 110+ in my 86 Mk2 for quite a while tho, I had it insurance company tow it to the nearest shop 30 miles away... Tow truck driver broke a tie-rod, I ripped him a new one and had him pay the shop. Mechanic said come here Bud, then showed me the blown 10A fuse... Live and learn.

So are you driving 110+?

no I don't push my car that hard it happen when I'm driving normally. I just got done putting the new engine harness on. But the starter is not turning been at it from 8pm last night till about 10 min ago I am going to give it another try tomorrow.

 

[ABNPayne]

Any luck w/ the new harness and the fuse?

 

[kakanator]

Any luck w/ the new harness and the fuse?

yes some how putting the new harness on stopped the fuse for going out. I took all the loom off the old one and some of the wires were cut then taped back so I don't know if that was the prob.

 

[benchwarmer]

That happens a lot. When I first got my first Supra it would do the same thing. Turned out the connector for the VSV was bad and the wires would touch when the stars aligned. Took me forever to isolate it.