jharriet

Hey guys Im trying to get my 4 runner going.
It's having fuel issues, the fuel pump receives 12v when I hit the key but immediately after it dies down to 0.2-0.3v. It was also blowing the 15a efi fuse. The wires going to the fuel pump don't seem to be corroded or shorting out anywhere to my knowledge. I traced them back to under the dash and lose them. I tried replacing the sensor on the air box, the afm I believe. And a few relays under the hood that I suspected to be faulty but got nothing still. I bench tested the fuel pump and it seems fine. I can't seem to figure it out.
I have another truck right next to it to salvage parts from.

I am curious if I run a 12v source to the FP on a toggle switch and install a inline regulator if it would work? I have tried the fuel pump to 12v and I can get the truck to idle, but it idles low and will die when I hit the gas. I'm hoping a regulator will solve that? But I'm not sure.
The truck is OFFROAD only so I'm not worried about legality of any modifications, I just want to get it going.

jharriet

I should add that I put good fuel in it and the tank seems to be clean, I cut a hole in the floor for easy access.

scope103

The fuel pump is powered through the EFI fuse, so you have a short somewhere.

First, jumper FP to B+. With key-on (not STArt), the fuel pump should run. If the truck can then start and run, your problem is in the VAF/COR circuit. http://personal.utulsa.edu/~nathan-b...87fuelpump.pdf

I suspect you have a bad COR; you get power to the fuel pump through the secondary COR winding powered by STA, but you don't get the relay to close with the VAF signal. You just need to trace this with your voltmeter (much more effective than swapping suspected parts).

By the way, if the truck runs with the jumper, you still have to fix it. The purpose of the VAF/COR is to remove power from the fuel pump if the engine stops sucking air. Without it, if you get in an accident that breaks a fuel line (easy to do offroad), you'll be taking a gasoline shower.

Flash319

I second scope103.
Also the pump only runs when the engine is taking in air through the AFM and thus the COR is pulled. These are not like chevs that run when the key is turned on.

scope103

Not quite. The COR has two windings, so it closes when the key is in the STArt position. Once the engine starts (and starts taking in air), the switch in the VAF closes and powers the other winding in the COR.

In the 21st century we'd just use a diode, but 80s technology required a special relay.

Flash319

Oh. I will have to take a look another look at the schematic.