EFI fuse problems

Hey all having some electrical issues with my truck. Have a 91 pickup with a 5vzfe (3.4) motor swap.

First happened about 2 weeks ago, EFI popped, got home swapped the fuse, was good for about 3-4 days before it went again. Same thing, just swapped it out and it was fine for a while.

last week though it started to blow the fuse and pop anytime I tried a new one. I have tried putting a tail light in the EFI fuse and the light has stayed on when I disconnected the fuel pump, circuit opening relay, disconnected computer. The 02 sensor harness isn’t touching exhaust either.

not sure where to go next if anyone has any ideas please let me know thanks.

 

Definitely sounds like you have a short somewhere, and one that's getting worse.

Have you used a multimeter to see if you have continuity between the fuse socket and the frame where you shouldn't?

With it being an electrical issue which is already hard to diag without it infront of you, and a swap with non standard wiring... Whew... I wish you luck!

Beyond that the fuse is a sacrificial link by using a bulb as a fuse your wire now becomes the fuse, current increases as resistance decreases best case scenario your wire becomes your fuse and melts, worst case scenario it burns your whole truck down.

 

So I believe the 5VZ engine uses a 20 amp fuse for the EFI system. Is that the fuse you’re using? If it is then I would also say to use a OEM fuse. Also check the wiring harness for any frayed wires.

 

Thanks for the replies, I have not checked continuity from bulb to frame I can do that after work today.

The light bulb in fuse socket is just for testing, truck can’t be driven right now. I believe the theory is that as long as it glows, the short is present and it should only be drawing 6-7 amps.

I’ve read the 5vz has a 20 amp fuse too, however I’ve been running a 15 since the truck was swapped and others I know with a 3.4 swap are doing the same. I believe the problem is somewhere in the stock 91 harness going to one of the components controlled by that fuse.

Has anyone encountered a short similar to the common 02 sensor contacting exhaust but in a more uncommon place?

 

Any Luck with this??

The O2 harness attached to the transmission if it was is good for rubbing wires .

Shorted Contacts or Coil in The EFI relay?

Which will open the Fuse when the Ignition is turned on.

 

Wyoming has the same thought as me. 02 sensor wires can rub and pop the fuse.

 

02 sensor has not been plugged in for awhile, used to have a 22re and had that problem it was my first suspect. I still pulled the harness through the floor of the cab and checked for a break and it was fine. I believe I fixed the problem, but i'm not sure how. I was using a headlight with 2 male prongs attached to the cut wires, plugged into the EFI fuse spot to find the short. the theory being, as long as the short is present, the bulb will glow. As soon as i began to lift my supercharger off, the bulb shut off. there was a wire bundle with no tape, or sheath around them between the motor and charger, wrapped them in electrical tape and I haven't had that issue again.

 

Hope you have it figured out.

Just because you have removed the o2 sensor does not mean the harness can`t still short

 

Truck was running great for about 3 weeks to a month, did some wheeling yesterday and handled fine, on my way home though the problem returned. Pulled the charger off first thing this morning and found a old harness that looked like bbq. Did a MM test and saw the wires all had 12v and was all copper. Put the headlight back in efi fuse slot, ignition on, touched wires to a bolt on fire wall and boom! Light on, take wires off ground, light off. Makes sense why pulling the charger off the first time immediately stopped the short and after some time the wire just found it’s way back to a ground. Will upload some pics. Thanks all for the help and replies
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Custom Wiring That looks to have just been cut off unless you cut the wires.

Then overtime Rubbed till they shorted at least it seems to have had some circuit protection to prevent a visit from the fire company.