puffenuf

Well I was just driving along and my 87 4runner died. No warning at all. Tried to start it a few times, nothing going. (It is fuel injected, 4 cylinder)
After a bit of process of elimination came to the conclusion it was probably my fuel pump.
Took my gas tank out to get at my fuel pump, realized there was a little access panel under the rear passenger side seat. What a PITA!
Anyways, finally found a bad wire connecting to my fuel pump connector.
(X marks the burned out spot)

wire to battery---------------------XXX{connector}----------------------wire to fuel pump

So I just cut out the connector, and thought I would just wire it straight.
Did that and it won't turn on the fuel pump.
I pulled the fuel pump, tested it on a bench, and it turns on just fine with plenty of sucking action! So I thought the pump just wasn't getting power from the engine.
Using a voltmeter I tested the wires running to the connector, and I am getting plenty of power.
Then I checked to see if I was still getting the same power when I connected the wires from the battery to the wires from the fuel pump, and nothing. There is no power there at all. It disappears somehow when I connect the two.
I thought maybe on the off chance that it needed pressure in the fuel line to run without triggering a sensor, so I hooked the fuel pump up to an alternate power source and ran my truck on that for about 20 minutes, and when I took that power source away, it dies.
I am completely baffled at where the power in the wires goes when I hook up the fuel pump and would greatly appreciate any help!
Thanks.

MMA_Alex

efi fuse blown? thats usually the first thing to check when you have fuel pump issues.

You're saying that the wires on the battery side of the truck have power, but when you connect them to the pump they loose power?

puffenuf

Yup that is exactly what I am saying. Wierd eh?
One thing to note is that when I cross the wires on the battery side of the truck, they don't spark? There is a power and ground line there, shouldn't that create a spark?

puffenuf

Oh ya, and the EFI fuse is fine. Any other suggestions?

MMA_Alex

they should only have power when the truck is running. If they have voltage and you touch them together they oughta spark, but you may not be able to see it.

It just sounds like the wires may be bad in a couple spots, and it sounds like they need to be totally replaced.

4Crawler

iTrader: (3)

Pump power comes from the circuit opening relay. Perhaps the contacts inside it are pitted or dirty and not making good contact. If you have a high resistance someplace between the battery and the pump, then it'll show 12V with no load (like your meter), but drop to 0V when you apply the load (i.e the pump motor). Track back the circuit and find out where the drop is:
- http://www.4crawler.com/4x4/CheapTri...shtml#FuelPump

dcg9381

Don't do that, unless you want to cause more electrical problems that you want to solve.

The fuel pump doesn't come on until the AFM senses air flow. If you want to test that circuit, you've got to jumper it (similiar to how you set timing). Do a google search. PM me if you can't find it.

Don't expect the pump to be on unless it's jumpered and the key is in the ON position.

A few things to check:
1) Resistance at the connector to the pump.
Report the value.
V=IR, 12 = I * R
I should be between 4-7, I'd guess... That puts R at 1.7 to 3 ohms... (approx)

2) rig a set of wires between the connector. Use a test light - or amp meter in the middle.