efi with fuel pressure problems

[dirtdrdave]

Yep test as lars suggested fuel supply line off at rail ,fuel pump jumped to run contantly you should expect 1/2 gallon or so with in a minute,,the flow should be like a garden hose ,,,,thats your volume test if ok proceed to pressure test again,, if not recheck before fuel filter if volume still low then your pulling tank.

With everything hooked back up reliable gauge at fuel rail jump pump to run constantly and expect about 30-35 psi ....next if you have a rubber section of hose in the return line to tank you can pinch off that hose and in effect your dead heading the fuel pump i'd expect at least 80 psi probable more like 110 psi...

So lets say volume is good pressure is a little low 24psi and dead head pressure is 90psi i'd say a regulator issue as an example.

Or volume low ,pressure low ....pump issue or possible low fuel pump supply voltage {voltage drop test} and/or a pump ground issue ....

As I think about this more, I guess I am in a normal volume, low pressure situation. That seems a little strange becasue the flow is so brisk. Would that still suggest a fuel pump issue? I can check the voltage at the pump. If the fuel pressure regulator was the issue causing low pressure, wouldn't I get a continuous return back to the tank effectively preventing any pressure from building up?

 

[SC74]

Can you plug the line with your finger - not crimping the line but using your finger print on the end of the hose to stop it? If so, you don't have enough PSI. I think you can only stop up to about 10 psi like that, maybe not even that much. You need in the 30-40 range.

 

[dirtdrdave]

Can you plug the line with your finger - not crimping the line but using your finger print on the end of the hose to stop it? If so, you don't have enough PSI. I think you can only stop up to about 10 psi like that, maybe not even that much. You need in the 30-40 range.

Tried that, can't really stop it, squirts around my finger like a garden hose would. The pressure gauge is confusing to me. When it was running, the pressure would read zero. I assumed the gauge was bad. I replaced the gauge once it stopped running, and of course, still reading zero. If I unscrew the gauge, gas will come out of the opening.
Moderately confused now!
Voltage at fuel pump wire at top of tank ok.

 

[dirtdrdave]

I never squirted starter fluid in the throttle body. I have spark so I assumed that was not the issue. Maybe I should go back and do that to be sure

 

[SC74]

Have you run codes?
Have you checked timing?
Unplug your idle air control and see if anything changes.

 

[DirtDonk]

I get no return through the return line, when all hooked up, but it will come out the return line at the fuel pressure regulator if that is removed. I assume the motor has to be running to get return out of the return line, because it has to run through the fuel pressure regulator normally?

Hmm, hoping someone comments on this, because it does not sound right to me. Even with the engine not running and no vacuum signal to the regulator, it should allow maximum pressure at the rails and still bypass the excess. Same as full throttle running basically.
At least that's my take on it.

The fuel pressure gauge still doesn't read anything when I hook it all back up.

Seems consistent with it not getting past the regulator too.
Remember the pump, when in good shape, is capable of almost 100psi output. The regulator is what necks that down to the 35 to 45 psi range.
So maybe you are still dealing with a low-pressure issue after all.

I never squirted starter fluid in the throttle body. I have spark so I assumed that was not the issue. Maybe I should go back and do that to be sure

i would at this point. Can't hurt to give it a quick small shot just to see if you get some fire (in the cylinders!) at this point.

Paul

 

[dirtdrdave]

I have checked key on engine off codes and they are just the standard codes, egr etc. There are no other stored codes.
I have not checked timing. Is it possible for that to just change on it's own? I guess the answer is yes, so I guess I should check
Unplugged the idle air control, no change.
Thanks for your help

 

[dirtdrdave]

Thanks.
When I try to plug the fuel line with my finger while the pump is running, it does squirt kind of like a garden hose, but it don't think it is anywhere near 100 psi!
I guess I;ll go get some started/lighter fluid and cross that off the list

 

[EPB72]

Quote:
Originally Posted by dirtdrdave View Post
I get no return through the return line, when all hooked up, but it will come out the return line at the fuel pressure regulator if that is removed. I assume the motor has to be running to get return out of the return line, because it has to run through the fuel pressure regulator normally?
Hmm, hoping someone comments on this, because it does not sound right to me. Even with the engine not running and no vacuum signal to the regulator, it should allow maximum pressure at the rails and still bypass the excess. Same as full throttle running basically.
At least that's my take on it.

Paul is correct ,,,,Assuming you have the stock mustang fuel rail and the stock fuel pressure regulator....but the OP said he removed the gauge and fuel came out the port, is this an aftermarket regulator with gauge combo???

my other post I'm assuming the gauge is on the fuel rail pressure port with the shrader valve,,?

little more detail on set up ..

 

[jhill52]

Paul is correct. Tou should always be returning fuel to tank. I think kit ia time to drop the tank. Sounds like a bad fuel pump.

 

[dirtdrdave]

Sorry, it is a stock (I think) mustang fuel rail with stock fuel pressure regulator which I assume is now 30 yrs old. The pressure gauge is at the inlet to the fuel rail and separate from the regulator.
I'm thinking the best course of action is just to replace both the regulator and the pump.
Any sugestions on the regulator? Stock or should I get an adjustable one?

 

[dirtdrdave]

Thanks for all the help and suggestions!

 

[lars]

Throwing a wrench in the discussion...

TFI module?

 

[dirtdrdave]

Throwing a wrench in the discussion...

TFI module?

I wondered about something like that. The day this began it wouldn't generate any power. It would stall if I tried to give it gas and would occasionally make a noise like a backfire, but not exactly. Then it hasn't really started since. I would think that if electronics were responsible, it would have ran or it wouldn't, not sputtered like it did?

 

[SC74]

Throwing a wrench in the discussion...

TFI module?

You're not the only one to think it. I am thinking it could be a spark issue as much as a fuel issue also, but not getting fuel through the return line makes me lean fuel. The zero pressure showing on 2 gauges is also suspicious.

Have you checked spark to any of the plugs?

Could possibly also be a MAF sensor. Try unplugging the MAF and see if anything changes.

 

[dirtdrdave]

I got some starter fluid tonight and it started. I guess that wouldn't rule out a TFI module failure as lars menioned. I tend to think that that is unlikely as it ran intermittently before it failed.
I unplugged the MAF sensor. That didn't help.
I will move forward with replacing the regulator and the fuel pump.
Does anyone have any suggestions on a regulator, stock or adjustable?

 

[DirtDonk]

While I like the idea of an adjustable one, I've never used one and the factory style has worked for many years and many millions of miles. So there's nothing wrong with continuing to utilize them.

There are still other things that can keep fuel from reaching the engine, but not many would keep fuel from the return line. Since it's just a big loop with only a few things in the middle, the list gets smaller. Never heard of a regulator stopping fuel completely, but I have to assume it's possible. I've had them apart, but can't remember even a small detail about them it was so long ago.
Not sure just how to test them either, but my thinking is that if your regulator was somehow able to block flow to through the lines, since it's at the far end of the engine side of things, you would still have fuel at the injectors. So why is that fuel not being injected?
Is there an in-situ test for injectors? Maybe your local parts store has a "noid light kit" you can rent/borrow to test the injector pulses. It's a light that you hook up to the injectors and it flashes each time the computer tells that injector to open and close. If you have a good pump and a good regulator and good plumbing, but the injectors are not firing, it would be good to know before buying a new pump and regulator.
And doesn't the TFI module tell the computer what's going on with the engine turning so that the computer can tell each injector when to fire?

I forget, what does the PIP test do? Isn't there an additional connector near the diagnostic port you can separate to put the computer into a different mode for checking the PIP signal?
Sorry I don't have the details in my head anymore. Just the vague notion that there are still other things that can help narrow it down.

Paul

 

[SC74]

If it starts on starter fluid, can you get it to continue running by feathering the gas pedal (or throttle linkage) and letting it run off of the fuel pump? Or does it die as soon as you quit feeding it ether?
If you can keep it running with the throttle, I'm thinking it's a choke/closed loop issue, like the motor doesn't know it's cold and not compensating. That leads me back to the IAC... but a lot of IF's.

 

[lars]

You wrote that you got fuel flow at the rail with the pump running continuously but nothing through the return line. Did you try disconnecting the return line at the tank and then running the pump continuously? The regulator is just a spring and a diaphragm on a restricted orifice. The engine doesn't need to be running for it to flow gas, and as Dirtdonk noted there isn't much in that system to prevent return flow. Even if there was, pressure would then build in the fuel rail to the maximum pressure the pump could deliver and the engine should still run, albeit rich due to the high pressure.

Electric in-tank pumps generally either work or they don't. If your pump is flowing fuel I wouldn't be in a hurry to drop the tank. Makes me wonder if the injectors are opening.

 

[dirtdrdave]

If it starts on starter fluid, can you get it to continue running by feathering the gas pedal (or throttle linkage) and letting it run off of the fuel pump? Or does it die as soon as you quit feeding it ether?
If you can keep it running with the throttle, I'm thinking it's a choke/closed loop issue, like the motor doesn't know it's cold and not compensating. That leads me back to the IAC... but a lot of IF's.

No, it won't keep running.