Ddecasas

My 87 4runner 22re is having that problem that no one can ever seem to give a good answer, basicly my fuel pump wont turn on sometimes and i think ive traced it to the Vehicle computer ,but before i worry about all that. in the meantime i need a vehicle. My question....

Is the fuel pump ALWAYS running when the vehicle is on?

Was goin to hook up a direct voltage line from the battery to the pump so i can turn it on when i need to drive. Besides the truck blowing up when i get into an accident is there any way this is going to ruin anything else?

Terrys87

iTrader: (1)

Anytime the iginition is on, the fuel pump will be on. I dont really see how the computer really controls the fuel pump and dont think it is your computer.

When the motor is cranking, it pulls your Air Flow Meter flap which energizes the Circuit Opening Relay ( located behind the passenger speaker) that energizes your fuel pump. That is the way that I understand it.

I would check your Cirucit Opening Relay. You can jumper these test ports in pic below to check and see if your fuel pump will stay energized. If you leave the jumper in, the fuel pump will not shut off with the ignition on and could cause a fire as you described.

How is your fuel pump? Do you run it on empty alot? The fuel systems get dirty in these trucks. How is your fuel filter? Fuel Lines?


Fp +B Fuel Pump Test for 87 and newer. Use a paper clip for better results.

scope103

Close, but not quite. With keyon-engine off, the fuel pump is NOT running. When you turn the key to start it closes the COR, AND when the VAF flap detects enough air flow, that will also close the COR (so it closes with the STA signal, and remains on with the VAF signal once the engine starts.) When the engine stops, the air flow stops, the COR opens, the fuel pumps stops, you don't get burned alive.

The rest of Terrys87' advice is spot on. Try jumpering FP to B+ to see if that makes the problem go away. If it does, you have a problem somewhere in the COR-VAF circuit. I would definitely suggest fixing the problem; you already know the risk of just driving around with the jumper in.

Ddecasas

Circuit opening relay is good checked it in accordance with the haynes manual also swapped it out with a 94 2wd that i got just incase. I also swapped out the mass airflow sensor so we can rule out those two i did also try that jumper, in your pic. Just ran that voltage wire straight from the batt to the pump 10 min ago and drove it around the block fine. Filter was one of the first things i checked a week ago. Also checked continuity of wires from the pump both ground and voltage good all the way till they stoped at the computer. Checked the ohms on the fuel pump relay, and that little 15 amp fuse for the efi is good too. Ive been digging the forums and manuals awhile, posted here as my last option.

jbtvt

Man, you really know how to make a guy feel wanted.

I keed, I keed

Can't say I've ever traced the wiring but according to the diagrams in my Haynes power is fed direct from the COR, not from the CPU. Not sure why it wouldn't be, the CPU controls pulse separately and the safety shutoff and pressure are all mechanical/electro-mechanical. Sure it isn't a break in the wiring insulation or corroded terminal? If you go ahead with the CPU replacement please post results either way.

scope103

As others have pointed out, there is no wiring from the pump to the computer, not even via the COR.

Testing individual components is usually a good idea, but if your "fuel pump [still] won't turn on sometimes," you either have an intermittent component (relays and the magnetic reed switch in the VAF, if shaken really hard, can open up), or you have an intermittent connection (relay socket, or a broken wire with pieces still held close by the insulation.)

So consider looking at the "big picture." Key on, press on the VAF vane until you hear the pump start. Now GENTLY tap on the VAF, the COR, gently wiggle the wiring to the pump. If the pump stops, you're very close to the problem.

Munkymag

I changed out my relays and it fired right up. Didn't have too go as far as you. I would hate too but check all the wires and connections real good like white on rice my friend. Keep us posted on your findings and good luck.

wyoming9

iTrader: (1)

One think to learn while you might have a good reading with your meter probe .

When connected via the plug it might not work due to corrosion .That the naked eye can not see.

Spent the better part of a day chasing my tail from this very problem quite a few years ago.

So any of the connections in this circuit very well may be the cause.

Ddecasas

Lol im one of those guys thats hates to admit he cant do something on his own.

Your completly right about the wireing got things mixed up, gunna try and chase some more wires :/

wallytoo

iTrader: (1)

define "on".

if you mean the key in the "on" position, then not necessarily. if you mean in the sense that the engine itself is running, then yes, the pump is on.

even though you direct-wired the pump, and it worked to allow you to drive around the block, it is still possible that the pump itself is beginning to fail, and will manifest itself as intermittent no-starts with the pump not operating. i coaxed perhaps 3 months out of a failing pump before replacing it on the side of the road in 10* weather (i had the new pump in the runner, just hadn't gotten around to installing it).

you also, as has been pointed out above, may have wire/connector corrosion or breaks (or loose fit). the jumper (paper-clip) test is a pretty good way to rule out some of the other issues, and to determine if the pump itself is going bad.

wally

Kiroshu

Possible Air Flow Meter fault based on symptoms. Even though you did say you tried other donner parts.

VAFM installed correctly..?

Electrical connections damaged/corrosion..?

Checked VAFM wiring harness for breaks and damage..?

Air intake hose broken/leaking..?

Any air leaks between the throttle body and the VAFM will affect VAFM performance and operation.

Terrys87

iTrader: (1)

Ignition on was poor wording on my part, I should of said while the motor is running. Electric is a weak area of mine so not much help there. Another possibility is there is a sock/filter on the end of the pump. I have seen them get a hard shell around them from a build up of the chemicals and such in the tank from the fuel. A possibility that the motor is starving for fuel and shutting off maybe?

Below is a picture of the filter on a carbed truck fuel pickup assembly, but I have seen it on the injected trucks as well. On the inside of a tank, it will look rusty. From my experience, once you clean a tank, there is no signs of any corrosion from rust, it is just a build up of chemicals. Rusty tanks happen from the outside where mud just sits on top of the tank and will put rust holes thru it.

I am just wondering if fuel starvation has you thinking it is shutting off. That build up around the filter gets glass like.

Kiroshu

X2 fuel system restrictions is definatly a possible fault.

McMagical Eng.

I am so glad I found this thread. I read the forums all the time but just joined and cant start my own thread yet. I have been searching like crazy for a list of things to try next. Just found a few bad ground connections, replaced my starter, sparks, distributor cap (all were worn out or totally fried, it wasn't just a shotgun parts swap approach) and checked my compression etc...
She finally sprang back to life... but only with the FP +B jumper connected, other wise it dies. I have done some multimeter testing on the AFM to check for problems and it seemed to check ok, but have not done the checks on my relays. I will definitely test those first before ordering a new AFM. Anyone have a favorite thread for pulling these things out and checking them? I would greatly appreciate any advice.

Terrys87

iTrader: (1)

Your Circuit Opening Relay is behind the passenger speaker on the dash. I have not been in your generation of truck in a long time to get access to the COR. If I recall right, the glove box assembly comes off quick and easy on the 89-95s and that will give you access to your COR.

If you need access to your fuel pump, on a pickup, I suggest lifting the bed instead of dropping the tank. There is not a lot of slack in the lines to drop the tank much.

The Haynes manual does a great job on testing the AFM. It has found two bad ones for me with its test. A new AFM from Toyota was $700 if I recall right. Might want to run some test on junkyard AFMs.