daleyboy

Well, I'm back to square one.

Gevo

Well, if you are getting fuel flowing through the pressure regulator bigger fuel line with the terminals jumped, then the fuel system is working well. If you are getting fuel at the pressure regulator while cranking, then the systems that control the fuel pump circuit are working.

But reading back, I'm a little confused if jumping the terminals eventually gives you fuel at the regulator or not. sorry if i missed something.

scope103

If the fuel pump is unplugged, it isn't pulling any current, so there shouldn't be any voltage drop in the fuel pump wiring. First, check the battery voltage right at the battery terminals, then at the battery clamps, with key on. You should have something like 12.6v. If it's below 12.1 or so, the battery is discharged (and isn't going to turn the starter).

Then connect the fuel pump and measure the voltage across it when it's running (usually by jumpering FP to B+). Now, you'll get some voltage drop through the wiring, but it shouldn't be as much as a volt. If more than that, the pump will be running slow and not able to reach pressure or flow.

If the voltage is low at the pump when running, back up and find where the voltage drop is. Check B+ to ground. If that voltage is adequate, the problem is the wiring from FP (about) back to the pump. If B+ is low, you may have a bad EFI relay.

daleyboy

It is NOT getting fuel to the big hose at the pressure regulator, but the pump is running, either jumping +B fp, or not. Gas is not getting from the pump to the rail. But what's stopping it?

scope103

Usually, the fuel pump can push up close to 100 psi. But the FPR opens (engine off) at 38-44psi http://web.archive.org/web/201003261...87fuelpump.pdf , "dumping" the fuel into the fuel return line to limit the pressure in the rail to that number. If your pump is pushing fuel as far as the FPR, but the FPR is not opening to "dump" excess fuel, that tells me your pump is so weak it's not making it to 38 psi. And if you have, oh, 10psi in the rail, the injectors will put in so little fuel that the engine won't run (too lean).

Another possibility is that the fuel line is completely blocked somewhere, and the fuel pump is just overrunning while holding somewhere around 100psi up to the blockage. If that were the case, you wouldn't get any fuel out of the CSI connector.

Could you have just a partial blockage? Probably not. If you did, that would restrict flow (so the truck would run poorly). But with the engine not running, and the fuel pump forced to run with the jumper, the flow past the blockage would eventually build up enough pressure in the rail to open the FPR. So if you put the fuel return to a container, you would see nothing when the pump started, but after a few seconds you'd get a reasonable flow.

IF you have bad (high-resistance) wiring to the pump (including the contacts of the EFI relay), that would weaken an otherwise perfectly good pump. So that it can't push out enough pressure.

You can check the pressure with a gauge. You can check the wiring by looking at the voltage across the pump while running.

Gevo

Also, when you say the fuel pump is running, you can tell because you hear it? If that is the case the pitch should be an indication of how 'strong' the pump is running. But, you'd have to have heard a properly workign system I guess to compare. I don't recall ever hearing my fuel pump.

daleyboy

I stuck my head in the wheel well, and got somebody to turn the key on. Yes, you can hear it, but it's not too loud. If you put your hand on top of the tank you can feel it too. I didn't work on it today. Trying to figure out my next plan of attack.

Gevo

I see. Well definitely check the voltage as explained by Scope. That's your next move.

scope103

With the jumper, I can hear my fuel pump standing at the diagnostic connector. I'm in a garage (not a lot of traffic going by to drown out the sound), and it is still not very loud. (I'd never be able to hear it with the starter turning.) i don't think I'd be able to pick out a pitch change as an indication of "strength."

But as Rad4Runner says, that's why you have a voltmeter. (in daleyboy's case, a voltmeter and a fuel pressure tester).

Last, remember that diagnosis is the process of deductive reasoning. it would be great if you could pop onto YotaTech, someone tells you "replace the TPS!", and bingo you're done. But it doesn't work that way. You have to play Sherlock Holmes. Just as a for-instance, if daleyboy has an internal leak in the fuel tank, his pump could be getting 12v and running at full speed, but unable to deliver 38+psi to the FPR. You'd need the fuel pressure tester to know that.

And so far, daleyboy is doing a pretty good job of mustering the clues.

daleyboy

I've got a good fuel pressure tester, but don't have the right plumbing that hooks up to banjo fitting. If I have to, I'll take the filter off and try to plumb it up to that fuel line. I hope I don't have to go that route.

Gevo

I don't think you have to worry about the plumbing being messed up between the filter and the pressure regulator or the cold start injector. Especially If you have a new filter.

You still haven't said if you tested the voltage at the pump while it was running.. or did you and I missed it?

daleyboy

I called the old guy I bought this truck from. He said that it had been blowing EFI fuses before he sold it to me. That's a big clue . I'll inspect the wiring all the way back to the pump. I know the oxygen sensor wire will make it blow fuses. If it's grounded against the exhaust pipe, but it's not touching. He said this truck has not been started in 7 months when he sold it to me.

tacomanut

that's interesting huh

daleyboy

Hi, me again. I haven't worked on this truck in a couple of days. Finally decided to tackle it again this morning. I checked all the wires for damage and bad connections, couldn't find a thing. I checked the voltage back at the pump, it's getting battery voltage back there. I checked out the old fuel pump that I took off of the truck and tested it on the battery, it ran strong. I can see how much fuel is at that banjo fitting, and know it's not enough. I'm missing something here

Gevo

Hmm, a quick thought... if fuel filter is installed backward would these be the symptoms? Can it be installed backward?

It still sounds like an electrical issue to me though :/ you said you checked the voltage at the pump again, but you checked it with the pump running right?

daleyboy

No, I didn't check it with the pump running

Gevo

Do that. If the pump isn't working properly due to wiring, if there is a problem the voltage should be significantly less when there is load on it.

daleyboy

Ok, had a chance to work on it this morning. I checked the voltage back at the pump when it was running, and only showed 2.54 volts. But, the pump was running, I could hear it. I know it wouldn't make enough pressure with that low voltage. I've checked all the wiring and can't find a thing wrong.

scope103

I assume "it" is the fuel pump, not the truck. How did you get the fuel pump to run? On 6/8 you suggested the pump would run with only key-on (not to start, not with your finger in the VAF, and no jumper). If that's what you're doing, there is something seriously wrong with your truck (okay, you knew that already). If you have anything more than 0v at the fuel pump under those circumstances, you could have a badly messed up COR that is "high resistance" whether or not there is voltage to the coil. So let's look for that.

First, check the ground return. With the fuel pump running, measure the voltage ACROSS the pump (back probe connector F6 at the tank), and also measure the voltage from each wire to a good ground. (the truck bed is NOT at ground, but the frame should be). If you get 12v to ground on one of the terminals, you have a high-resistance ground return. Next, check voltage to ground at FP. That should be a direct wire to the pump, so it should be the same as at the pump. If different (higher) then you have a bad wire to the pump. Then, check voltage to ground at B+ (no jumper). That should be 12v with key-on, if less you have a problem in the EFI circuit.

What were you looking for? Electrons dripping out onto the ground? Wiring different from the EWD you don't have? Okay, the first thing is always to check for obvious mechanical damage (cut wires, etc.) But if you have a corroded connection anywhere in the electrical system, you won't be able to see that just by looking with your eyes. You need to use your multimeter to isolate where the voltage changes from what you expect to what you get.

Gevo

LOL... That would mame life significanrly easier though, wouldn't it?

Maybe a spray of some wort and some black light like they do on csi to find blood
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