yoda91
I have a 1991 4runner 3.0 that the efi fuse keeps blowing. I have checked o2sensor wires and they look good. Replaced injectors, fuel pump 02sensor. It only happens when pulling a hill ,when it blows you can put in a new fuse and be on your way. If I in hook the o2 sensor I can go a lot further before it blows if you drive on the flats you can go for ever. The last time it happens it took a wile before it would restart
( would start then pop circuit breaker ) any suggestions would be appreciated
Thanks Yoda 91

 

yoda91
I have a 1991 4runner 3.0 that the efi fuse keeps blowing. I have checked o2sensor wires and they look good. Replaced injectors, fuel pump 02sensor. It only happens when pulling a hill ,when it blows you can put in a new fuse and be on your way. If I in hook the o2 sensor I can go a lot further before it blows if you drive on the flats you can go for ever. The last time it happens it took a wile before it would restart
( would start then pop circuit breaker ) any suggestions would be appreciated
Thanks Yoda 91

 

I'd start by sitting there (key-on) and slowly pressing the accelerator to the floor. You "could" have a (very) bad TPS, but it still might take the vibration of driving to trigger the short. So next you could try gently jiggling the wiring, with the accelerator floored.

Not as likely, but I suppose a shorting VAF could trigger the EFI fuse. Use your finger to move the vane.

Other than that, I can't think of any other electrical connection that is made with engine effort / vacuum. Perhaps someone else can.

 

According to the wiring diagram, the EFI fuse powers up the following:
- Fuel pump
- O2 sensor heaters (two of them on a California truck)
- The "always on" portion of the ECU. (correction: ALL of the ECU)
- Assorted VSV's.

Given what you've written, I would most suspect something in the O2 sensor heaters and/or wiring. Could be a connection at the exhaust pipe that shorts when it gets hot, which will happen when you load the engine going up hill.

Is this a California truck with the dual O2 sensors?

 

There are two threads with the same thing. I am moving irab88 post to here and will delete the duplicate post.

 

Thanks for the info I'll check the tps and the wiring again. I replaced the o2sensor thinking it could be shorting out when it heats up, I can drive further up hill now but still fuse still blows.( I have replaced the fuse with a circuit breaker )when the problem happens if i go down hill it goes away if i continue up hill it blows faster until it wont start again .once it sits for a wile then shes ready to go.
thanks for the help,
yoda91

 

and yes this is a ca. vehicle, and as near as i can tell it has 1 o2 sensor befor the cat and a heat sensor in the egr

thanks again
yoda91

 

Start it up, let it idle. Get underneath and start tugging all harnesses toward the rear of the vehicle. When the fuse blows, the one you just touched is shorting to ground somewhere.

 

Also I'm not talking off road hill just driving on the hiway hill

 

I'm also not talking about tugging like you're lifting an engine. Gentle pulls is what we're going for. Chances are wherever it's shorting at, it's only moving 1/16 of an inch to do it.

 

In taking you advice and checing the wires at the rear of the vehicle I found some melted to the top of the tail pipe I'm going to repair them and try it again this evening
Thanks again will let you know the out come
Yoda91

 

 

X2

 

x10

 

problem solved, one of the plastic keepers on the frame broke allowing the wire harness to sit on the top of the tail pipe (3 wires melted) this looked new, wile pulling the wires out of the loom I found another wire (about a foot away) that was broke in half,this looked old like it was the original problem.
thanks again for the help
yoda91