Well guys, don't know where to start, but here it goes.Efi fuse continues to blow. Before I took it to the shop, 3 times of course, this is what I have done, that is after reading the manual an going through you guys post.#
1. Checked the main relay, good continuity, between 1-3. #2. Checked Circuit opening relay resistance, Sta-E1 =21.9, Fc- b+ =110, Fp-b+ infinity, is that good? #3 Replaced gas pump, an filter.checked, all wiring harness, including 02 sensor.#4 Not to mention replacing the wiring harness( which I plan to return).#5 took it to 2 previous shop couldn't fine problem, so I wasn't charged.my last resort was the Toyota dealership, since they couldn't fine the problem within 3 hrs,I wasn't charged the $115, for them to go more in depth, an fine it, that would be $346,diagnostic.guys I'm done with ideas. Can someone help me. The last check I did this morning was jumping B+ an Fp to hear the fuel pump only to Blow the efi 15?once again. I am here in Tennessee an planning a trip to see my daughter in Ny. Driving my 91 Yoy of course. I have faith it will happend, with a little determination an some help of course. Last but not least. It all started when the truck started cutting off, without the fuse blowing. I thought it might've been the pump an filter.which i then replaced. I thought it was fixed because it ran for 12 miles.then the fuse problem occurred.
Again, what would cause the fuse to blow after jumping the Fp and Bt, wanting to jump the fuel pump? Thanks for your time!

 

IF jumpering B+ to FP blows the fuse (and you can sit there with key-on indefinitely otherwise), then the problem is in the pump wiring. Duh. The FP runs directly to the fuel pump. Of course, it connects to the COR on the way by, but the COR is not closed with key-on, not running. So it's not the COR, but it could be bad wiring in the COR socket.

Tracing that wiring may be what you have to do, but before you get into that check the O2 sensor. That wiring hangs out in a hellish environment, and if the sensor wire shorts to ground (or it could be the heater wire; same bundle) it will blow the EFI fuse.

 

The o2 wires is clear! Where do fine the COR wiring? An the Heater wiring?

 

We checked the resistance in all sections of the fuel pump wiring harness. No sections had high resistance. We used a multimeter to measure current draw on the fuel pump circuit with the truck running. It measured 31.07 amps max. We can't find a bad spot in the wire harness for the O2 sensor or any of the other typical problem spots. Any other ideas? Oh and the fuel pump harness got pretty warm to the touch while the truck was running (pulling 31 amps).

Thanks in advance for any help. It is all greatly appreciated.

 

31 amps is way too much load for the fuel pump. Something is wrong there. Investigate further.

The heater wiring that was refered to is the internal heater in the O2 sensor, that wire is one of the wires that goes into the O2 sensor itself.

 

I have to agree with Scope103

Wait a minute are you trying to jumper B+ to FP with the ignition turned on ??

If it arcs it would pull enough current to open the EFI 15 amp fuse .

You are replacing with the correct fuse ?? (I have seen this all to often)

If your not the fuel pump circuit .

What brand pump ?? Bad out of the box??

Pinch the wires in the fuel pump bracket

Just how did you check the wires Ring them Out??

 

I would still lean on the o2 sensor harness where it goes overtop of the trans. This is a frequent chafe point and had been the root of many blown efi fuses when I had my '94.

 

I don't know the actual number for the fuel pump, but millball is right. 31 is WAY too high (that's around 400 watts; a headlight is only 35watts)

Your problem isn't high resistance in the harness, it's low resistance to ground somewhere. MOST likely you've got a worn spot somewhere, that when jiggled makes contact with the frame and shorts out the EFI fuse.

I should point out that the fuel pump is powered through the 15amp EFI fuse. If you measured 31 amps, either your measurement is wrong, you have the wrong fuse, or for an instant that 15amp fuse was really sweating!

 

It's a new wire harness, an I hadnt start the truck since the change.

 

It's a brand new pump from Auto Zone. Life time warranty. Yes I jumped it with a paper clip, with the 15 fuse. Yes with the ignition on.

 

It's a new wire harness, I've checked the o2 wires, it's all in tack.

 

So you recently installed a new fuel pump, and replaced the O2 sensor harness. Now, something downstream of the EFI fuse is shorting out. Do you see where this is going?

I assume you can get key-on (which will power the o2 sensor) without blowing the EFI fuse; that suggests it's not the o2 wiring (at least until you start jiggling it by driving), and not the wiring up to the COR. My guess is that something happened at the fuel tank (pulling on 20 year-old wiring will do it) so now you've got an intermittent short back there.

 

Like ^^^. THOROUGHLY Inspect the wires for that fuse all the way to the fuel pump for pinching or chafed insulation that allows short to ground

 

We thought the current measurement was high also. Here's how we set up the test.

1)Pulled the 15amp efi fuse out of the fuse block.
2)Set a multimeter to measure ampereage with a lead going to each contact of the efi fuse block.
3)Try starting the truck.

To our surprise, it cranked up and ran with the multimeter in place of the fuse. We let the truck run for 30-40 seconds observing the current draw. 31 amps was the max but it did stay around 24-28 amps. We'll recheck the O2 portions of the wire harness for bare spots just to be sure.

 

Pretty much a no brainer drawing over 20 amps on a 15 amp fuse !!

Drawing through the Meter it alloweda complete circuit nothing opened .

Now my Question is that Auto Zone pump made that it draws the high of current like that or a defect Being Auto Zone how many will you need to replace till you get one that works ??

 

That pump probably is supposed to pull between 3 to 8 amps in normal use. So it's either defective or there is alot of other unknown loads on that node.

 

[QUOTE=Diego toyota;52326793]

Second that.

 

Once you jumper B+ to FP the fuel pump should be the only load .

The word here is should one never knows what might have been wired into that circuit

 

Try leaving the key off, put the multimeter back in the fuse position like u did before, then jump B+ to FP. That should give u a true reading on what the pump is pulling, and not whatever else is attached to the efi circuit is also pulling

 

The two posts above are exactly right. Don't overthink it. You had it narrowed down when you blew the fuse with the jumper wire on while not trying to start it up. If you want to rule out the wiring back to the pump, wire the pump to a spare battery through your meter and measure the load. Remember though that your are dealing with fuel so use caution if you try this. If you don't feel comfortable with it, don't do it.

Sounds like a faulty new pump. I hate aftermarket electronics. I see issues with them all the time. Had a new aftermarket alternator overcharge and blow four batteries at once and burn the whole dash up in one of my freightliners at work.