fountain

I had trouble once about a week ago where the truck blew the fuel pump fuse and died. Took it in and fixed it..simple fuse swap...yellow 20 amp under hood in fuse box. Everything seems fine. Been driving about 20 miles and did it again and now it keeps blowing the fuse when I try to swap it out.
Anyone ever seen that before? What could be causing this?

AKHeathen

replace the fuel pump period. it's much like the blower motor. you can kick it, put in a lrager fuse, etc, but bottom like is the motor is drawing far mare then it should. the fuse size is tha mount of amperage the circuit can handle in a short intant, not what it should support. when it draws more than that, it blows protecting against fire. the pump actually pulls like 12-16 amps normally. i only go into detail about this because i've seen too many people try to get around the fact that the motor is shot and waste a bunch of money and parts. just get a new pump and be done.

fountain

So you're saying that the pumps are weak and drawing more than they should be. Makes sense.
But why is it blowing the fuse at the turn of the key..as soon as it begins to turn over it wil blow em....it barely makes contact.
In thought, it should blow the fuse just by turning the key to "on" and not even cranking. Correct?

fierohink

Look to see what else might be on that circuit. If you have an oxygen sensor short out it blows the EFI fuse. Go figure.

Terrys87

iTrader: (1)

I would suspect the fuel pump filter may have gotten a coating around the fuel filter at the end of the pump. Below is a filter for a 22r but the basic idea is the same. Your filter will be more of a flat style filter. I wonder if it just got caked up and put your pump under alot of strain.

I would check to see if the wire to the pump has flopped around and gotten a bare spot on it shorting it out.

I think the pump does kick on for a few seconds with out the motor cranking. If that is the case, it would blow a fuse if it is shorted or if the pump has shorted itself out.

A Denso pump is what is factory installed can be a little pricey and well worth the money. I get my generic pumps off of ebay that are an exact fit for a lot less and have never had one to fail yet.

Also dont run your tank on empty. Fuel is actually what cools the pump. Running on empty will kill a pump. Not sure if you have done that but just to let you and others know. I dont let mine get below a 1/4 tank and very seldom do I go belwo 1/8th tank.

wyoming9

iTrader: (1)

Hello !!!

You now Have a dead short someplace in that circuit !!!

Which means as soon as the circuit is powered you have full battery voltage going to ground .Which causes the fuse to open.

If all that was on that circuit was the fuel pump I might agree it is the pump

Might very well be the fuel pump could also be the circuit opening relay could be physical damage to the wires . Poor connection ??

Since you don`t mention just what fuse opens or just what your working on it is a hard call to make just where the issue is

Just which one is the fuel pump fuse ???

Maybe I just have good luck But I have yet to change a fuel pump. on any of my fleet.

scope103

C'mon, this isn't kindergarten. The color of the fuse doesn't tell you much. There is no "fuel pump fuse," but the fuel pump does run on the EFI circuit. Not so good: there are NO 20 amp fuses under the hood. http://personal.utulsa.edu/~nathan-b.../2powersou.pdf The EFI (MFI) fuse is supposed to be 15amp; could someone have "fixed" this problem before?

No, not correct. The fuel pump does not turn on until you turn the key to STA (start). Then the VAF has a switch that holds the fuel pump on (through the COR) once air is flowing.

This is (of course) good advice; many on this site have reported blowing the EFI fuse when the O2 sensor wires have shorted to ground. Those wires are in a hellish environment. And they are so easy to check that you should do that first.

Is it a problem with the fuel pump? Don't guess, don't swap parts randomly, TEST. The FP line in the diagnostic connector bypasses the COR and goes directly to the fuel pump. You COULD use your multimeter to check for a short to ground, but the resistance of the fuel pump is so low (probably less than 5 ohms) that you might have trouble that way. But do it; that's one of the 1,000 reasons you have a multimeter.

Still not sure? You've already got a box of 15 amp fuses; just use jumper clips to power the FP port directly from the battery through one of those fuses. If the pump runs, it's good. If the fuse blows, either the pump is shorted or you have a short in the pump wiring. (Either way, you're lowering the tank to get at the wiring on top or to the pump.)

Good luck!

wyoming9

iTrader: (1)

To help stimulate the economy it is just better to keep changing random parts till by pure luck you might get lucky !!

Kindergarten was the best year of School I did not get yelled at for sleeping!! It was the only year I learned anything.

AKHeathen

lol, that same line of thinking is why people spend $500 in fan control switches that burn up/melt because the fan motor is worn and drawing excessive current. it's the same thing for a fuel pump. and to answer the o.p.'s question, it's because the fuel pump does not come on until the door swings past park in the vafm. it is turned on only when you crank, and when the air door swings open because the engine is drawing air...... or you manually jumper the fuel pump on.

AKHeathen

i don't know of any other circuit on the efi fuse that energizes on crank and not run with engine off.

fierohink

Exactly as AK said about when the fuel pump energizes.

To test this:
Open top of air filter box so you can get to the vafm.

Replace fuse with a new one

Turn key to run (not start).

Push paddle on vafm and see if your fuse pops.

fountain

I did it yesterday..put new fies in and turned key to on and it was blown when I checked it.

RAD4Runner

As scope103 says ^^^
Look at schematic and inspect all circuits that take power for it for worn-out insulation causing short to ground.

A problem well-stated is a problem half-solved. What year-model?
Need to look at schematic, and we need to know what year-model so we know what schematic to look at and which fuse block you're looking at?

scope103

No, the fuel pump comes on with the key to start, and continues to run with the key back to run due to the switch in the vaf. The COR has two windings (one driven by STA, the other by the vaf) to act as a 60s-era "OR" gate.

You might be able to get the truck to start with only the vaf controlling the fuel pump, but you would have long cranking times.

RAD4Runner

Like Scope103 says^^^

If 1986-1988 4Runner 22RE, here's how C.O.R. works.

fountain

the truck is a 94 22re

AKHeathen

nope. even though i have the circuit memorized, i walked 10 feet to mine with the vafm top open and tested it many ways..... it is a very simple "or" relay. either it's cranking or the vafm is not parked and the fuel pump will be on....unless the efi fuse or relay is bad. it's quite similar to a ng dryer solenoid system. you have start and hold coils. manmy many other ecm controlled fuel pumps are another story as you described, but not this.

AKHeathen

wow i tried to multiquote those yesterday, even after 2 restarts they appear out of nowhere, lol.

Terrys87

iTrader: (1)

I looked at my Haynes Manual (Page 12-17) and the Fuel pump is on the 15Amp EFI Fuse. Some of the other circuits are Circuit Opening Relay, Air Flow Meter, Throttle Postion sensor, Oxygen Sensor, Check Connector. Everything listed is going to be under the hood except the Circuit Opening Relay and O2 Sensor. I would check to see if there is any damged wires shorting out. That is the extent of my electrical trouble shooting.

fountain

o2 sensor wires on the exhaust