Old Topic it seems: EFI fuse keeps blowing

[MA71]

I know this has been covered, and I've read the threads and done what the people have suggested,, but I have had no luck with any of it and my car is still broken.

The problem:
The EFI fuse is blowing every time I try to start the car. It pops immediately.

What I've done:
I've taken an OHM meter to everything I can think of between the fuse box and the ecu and tested them as per TSRM specs. so far everything is apparently still good. I have visually inspected the harness and havent found anything that looks bad or is grounding out. I checked the harness to the OXY sensor and its good, even unplugged it to make sure. The harness over the EGR is still in its clip too and is not resting on top of the EGR tube. The car has 550cc injectors so I checked where I spliced them in and everything still looks totally good.

Are there maybe any other problem areas for this?? Any suggestions at all?? It has been almost a month that my car has been out of commission and I'm at my wit's end, almost ready to take it to a shop.

If anybody has any further ideas or suggestions please throw them out, anything helps at this point.

Thanks a ton
-Ben

 

[MDCmotorsports]

Ben,
Its a dead short some where. Typically its in the 02 sensor circuit.

 

[TooGoode]

is your fuel pump taking a crap? pulling more amps than normal? i had the efi problem and had a topic on it as well. it ended up being my throttle plate hitting my wiring harness and grounding out.

 

[MA71]

TooGoode,
I read your previous post and looked at my throttle plate area and its fine.

And its not the oxygen sensor circuit, I checked that as well.

as far as the fuel pump, I'm not sure actually, havent checked that. Do the pumps on these cars die like that? just, poof, out of nowhere? And would it be causing this?

 

[MA71]

just thought of something: could running the 550's/Lexus AFM put too much strain on the stock pump and cause it to go out?? I know that people usually run a walbro but I didnt think it was a necessity...

?

 

[jdub]

If the pump went out, it's not because of the Lex/550 combo.

You can put a 12V light on the fuse holder terminals and start checking wires with the power on...unplug the ECU. If the light goes bright you found the wire.
Did you remove the box from it's mounting and have a look under it?

 

[MA71]

I replaced the fuse box, still a no go.

The 12v light would just be telling me which leads are grounding out correct? I have already taken an OHM meter to the box and know which ones are grounded.
Maybe I dont understand the process though, am I supposed to unplug the ECU and Then test the terminals?

 

[fonz87]

check your CPS plugs, see if it's plug! My EFI fuse popped when i didn't have that plug in.

 

[MA71]

checked the CPS. it looks ok. The plug is fine. there is one wire inside of it in which the insulation is *almost* warn through, but its not touching anything/grounding.


I just had a friend suggest to bump start the car, implying that it could be the ignition switch. I'm inclined to think that if the ignition switch went out it wouldnt be causing the EFI fuse to blow however, and I have already checked the little ignition box located by the fuse box in the bay.
The car is parked on a hill, so bump starting it would mean Pushing it back up that hill (pending it doesnt start).

thoughts?

 

[jdub]

Take a look at the TEWD power source for the EFI fuse:
http://www.cygnusx1.net/supra/Library/TEWD/MK3/manual.aspx?S=Main&P=33

Is the starter anywhere in it? Does the fuse blow when the ignition is turned on?

Plugging a 12V light into the EFI fuse holder with a short will illuminate the light. As you trace the wires, if the light goes out, you found the short:
http://www.cygnusx1.net/supra/Library/TEWD/MK3/manual.aspx?S=Main&P=46

The purpose of unplugging the ECU is when you put a light bulb in the EFI fuse holder you defeat the purpose of the fuse. I don't want you to potentially fry the ECU.

 

[MA71]

Thanks, I should have some time tomorrow to check some more things.

Regarding the fuel pump, is there anyway to test it with the EFI being blown?? I know you're supposed to jump B+ and FP in the diag box to test the pump, but with the fuse being blown it wont work anyway. So is there another way to test the pump without dropping the tank and testing it directly? (also how big of a pita is it to do that anyway?)

 

[jdub]

Does the fuse blow when the ignition is turned on?

Can't help if you don't answer.

 

[MA71]

sorry about that

When the ignition is "on" the fuse is fine, it does not blow until you attempt to actually start the car

 

[jdub]

In that case, I would start by looking at the FP up VSV, EGR VSV, O2 and ISCV wiring. The wiring to +B in the diagnostic block too. The circuit opening relay wiring path to the EFI main relay is suspect as well.

 

[MA71]

I finally got a chance to test the fuel pump as per the specs in the TSRM and when I attempted to jump +B and Fp with the ignition ON the fuse blew. The fuse normally does Not blow until I try to actually start the car (normally its still ok when the ig is just On).

Before I go dropping the tank and replacing the fuel pump I just wanted to double check with you guys that this could/would indeed be the issue. Logically, if the fuse is blowing as soon as we try to jump the bump, then the pump is bad, correct?

Thanks guys
-Ben

 

[jdub]

Not necessarily. You need to trace the FP wire in the EWD...I am not home right now and do not have access.

 

[MA71]

Here is the part of the wiring diagram that I am interested in. Unfortunately reading these things accurately is not my forte and I'm still learning, so I just wanted to attempt to clarify with you all.

It appears as though the Fp lead from the "check connector" box (the diag center) does connect directly with the fuel pump. It also however continues on to go through three relays and a resistor before getting to the EFI fuse.
Does this matter?
In terms of finding my short, does this still mean that 1. it could be anything in the circuit (because the Fp lead connects to it all) or 2. that it is most likely the fuel pump because it is also directly connected to it?

ok that just sounds complicated typed out, sorry. Hopefully those of you smarter than I can decipher my ramblings and my situation and can come back with a more definitive answer.

Please and Thank You.
-Ben

 

[3p141592654]

You will need to troubleshoot the fuel pump wiring, but at least you are narrowing down the problem.

I would start by disconnecting the FPU relay and resistor on the passenger side fender, then retest. If it still shorts then you will need to disconnect the connector to the fuel pump at the tank. There is also a connector in the left kick panel (see page 30 of the TEWD it's G1 pin 7)

 

[MA71]

Thank you, I tested as you directed and got the following:

Amongst testing the other components, we discovered that with the FP relay Unplugged it did Not blow.

Before I go buying an $85 dollar relay, this DOES in fact mean that the relay is bad, correct??

Thnx

 

[3p141592654]

To be clear, we are talking about the fuel pump control relay (L) and not the circuit opening relay as shown in link below.

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=46

If so, its just a simple SPDT relay, so easy to test.

I would start by measuring resistance between the case and the 5 connectors. All should be infinite. Any low resistance to ground will cause the fuse to blow.

Next I would measure the coil resistance between pins 1 and 3 (yellow and blue-black on my 90). Should not be shorted.