in tank fuel pump

[1986 danger ranger]

Im trying to chase down a low fuel pressure problem and have dropped the tank

I just need to know if there is supposed to be power to the tank pump when the key is in the run position. I assumed there is supposed to be. I can hear the pump on the frame rail energize, but I'm not getting any power at all to the in tank pump. at least Im not getting anything with the volt meter

I also noticed why my fuel gauge is dead, the float has cracks and it filled with fuel!

If anyone had any pointers or insights I'd appreciate it!

Thanks

 

[94 lngbd]

There should be power other wise you wouldn't be getting a proper amount of fuel. I beleive that the pump in the tank is of a low volume, to pump the fuel up to the high volume pump thats on the frame rail

 

[1986 danger ranger]

and that's exactly my issue. I'm not getting proper fuel pressure, and the truck runs poorly. I'm just trying to diagnose whether it's electrical, or the pump itself. assuming the high pressure pump is working properly...

My only wonder, is if the power is run through the same wire as the high pressure pump, so when that kicks off prestart, it also kicks the low pressure pump off. Basically all I want to know, is if the circuit to the low pressure pump is always closed when the ignition is in the run position.

And is it correct to assume that I should be reading 12v when I actually get voltage to it?

Gas motors, and all their mechanics, is a little foreign to me. I'm highly familiar with diesels, and more specifically, the 12 valve cummins.

 

[Jim2]

and that's exactly my issue. I'm not getting proper fuel pressure, and the truck runs poorly. I'm just trying to diagnose whether it's electrical, or the pump itself. assuming the high pressure pump is working properly...

My only wonder, is if the power is run through the same wire as the high pressure pump, so when that kicks off prestart, it also kicks the low pressure pump off. Basically all I want to know, is if the circuit to the low pressure pump is always closed when the ignition is in the run position.

And is it correct to assume that I should be reading 12v when I actually get voltage to it?

Gas motors, and all their mechanics, is a little foreign to me. I'm highly familiar with diesels, and more specifically, the 12 valve cummins.

I just went round and round with this myself... (1988, 2.9L)

When you first turn the key, the in-tank pump only runs for a few seconds. If you test it after those few seconds, it will show no power.
.. at first, I didn't know this, and I burned out a good pump by running a jumper wire direct to the battery... :/

To make a long story short, the problem with mine turned out to be the black/green wire that connects to the negative battery terminal. Once I connected it, the fuel pressure came right back. It sits at 31psi @ idle now.

The inertia switch would be another simple fix (if yours is tripped).

As for voltage, I'm not sure what it should be at the tank... but, iirc, mine shows only 10.6 V at the plug for the frame pump.

What exactly do you mean by "running poorly", and how much fuel pressure do you have right now?
Before I fixed that black/green wire, I had about 12 psi and the truck wouldn't run at all.
Now, the truck screams @ redline... but I still have a slight hesitation coming off idle. (but there might be other reasons for that... not sure yet)

 

[1986 danger ranger]

my pressure is 25ish psi I think. It was a little while ago that I tested it. I've been told that the injection system is cranky on these trucks and that the fuel doesn't atomize properly if the pressure is even just a bit too low. given that the specs are 32-40psi (IIRC), I figured I'd try to find out why it's low, and that maybe the low fuel pressure was related.

It's hard to explain what exactly is going on. It doesn't start too good and it won't idle for more than 10 seconds or so before stalling if I don't give it some throttle. and even when I do that, sometimes it wants to stall on me. It goes through cycles though. It's like it will want to run perfect for a couple seconds, and then act like it has a miss and will fall on its face, then run fine for a moment again. like that, back and forth. More on the running crappy side of things though, and it has NO power. Can't even get above 40mph to the floor. It backfires sometimes too. Like yours, it has a hesitation at idle too, most of the time.

And I have no idea what the inertia switch is.

This is my second motor, and the problem remains the same. Well, more or less. The first motor did this (also ticked like a type-writer) but I could usually get it up to 60 and maintain my speed but when I tested my fuel pressure on that motor it was good at 40psi (swapped the motor because it finally wouldn't start, and I figured something let go inside the motor), and then I swapped it out for this motor, which runs beautifully, except for this nagging problem which is the same, but worse than it was with the first motor.

Before I swapped the motors the timing was checked, the resistance on the plug wires were checked. Basically everything checked out on the first motor. So I swapped the motors. Same problem, but now it's worse, and this time my fuel pressure has dropped, figured I'd fix one thing at a time.

I suppose the issue could be the regulator too, but given how bad the fuel filter was when I changed it and that there was water in the bottom of the canister I figured I'd drop the tank and see what's going on in there. There is a LOT of rusty, nasty chunks and crap in there, so I'll clean it out anyway, so all is not lost regardless and I need to reseal the vent cap thingy too. There's a clear path to the outside world from the inside of the tank so that has to be fixed anyways.

I want this thing up and running as it should though! it's driving me nuts!

 

[Jim2]

...And I have no idea what the inertia switch is.

This is my second motor, and the problem remains the same...

The inertia switch is on the lower firewall, inside the cab, passenger side... in front of the passenger's left foot. I guess it's a safety item, and I doubt the truck would run at all if it was tripped.

I only mentioned it because it could've been a simple fix.. it looks like this;

Did you replace the harness when you swapped engines?

I'm not a mechanic, but if you're using the same old harness, I would consider it to be a suspect.
On mine, the plastic that covers the wires is brittle, and there's quite a few places where it was showing bare wire inside. I taped up everything I found... (mostly under the hood, the interior wires were in better shape)

There's a lot of good schematics in this link, (just gotta look up the one that applies to yours..) http://www.autozone.com/autozone/re...DIAGRAMS/WIRING-DIAGRAMS/_/P-0900c152800781b2

I'm not real good with electronics, but I would recommend checking the wires to the fuel pressure regulator and the fuel pump for starters, and then test them from end to end..

When I was working on mine, I neglected to follow it "end to end", and it wound up taking me a long time to realize that it was as simple as connecting that black/green wire to the negative batt cable.. it was many many hours before I found that 5 minute fix.. but at least I didn't have to buy any more parts...

Good luck with yours, I hope you find that it's something simple!

EDIT - sorry, my memory was off... there might not be any wires that go to the fuel pressure regulator..

 

[Jim2]

ps, look for the wires to the fuel pump relay too..

 

[94 lngbd]

If it doesnt get above 40 mph it could also be a clogged catalytic converter