efi with fuel pressure problems

[dirtdrdave]

Hi All,

I think I have a fuel pressure problem. I have an original 302 with mustang efi using an RJM harness. Recently it was off the road for an extended period while body work was completed. At that time, I also installled a painless wiring harness. It was running well but only for a few weeks. One day, it began sputting and stalling producing no power. I towed it home, now it won't start. It sounds like it is about to fire, but doesn't. I do have spark. Interestingly, my fuel pressure gauge was registering zero when it did run. I assumed it was bad. I changed the gauge and now it still registers zero when I am cranking it and fuel pump running. I have a bc broncos tank with the fuel pump inside. I can hear the fuel pump running. I changed the fuel filter, that did not help. I removed the vacuum hose on the fuel pressure regulator. There is no gas coming out of the top. When I remove the fuel pressure regulator or the fuel pressure gauge I do get fuel leaking out.

Could the fuel pressure regulator be causing this issue?
I can hear the fuel pump running and do get some fuel as I mentioned when the pressure gauge is removed. Is it possible that the fuel pump is delivering fuel, but just not at a substantial pressure?

Thanks for reading! Any help is appreciated!

 

[rjrobin2002]

Disconnect the fuel line from the regulator and see if it's flowing a good stream into a bucket when you turn the key to on. It should do a 1 second prime.

Also, shoot some starter fluid in the throttle body and then try starting it and see if it will run a few seconds.

 

[73azbronco]

Fuel pressure and fuel flow are step one in an EFI trouble shooting guide.

Try fuel into bucket mentioned above. How old is the gas? How is the filter?

 

[billtammy]

If your sure there is gas, the short piece of hose in the tank can rupture sending a tiny bit of fuel but not enough pressure to the rail. If that is your problem be sure to use fuel hose rated for fi and submersion.

 

[dirtdrdave]

Disconnect the fuel line from the regulator and see if it's flowing a good stream into a bucket when you turn the key to on. It should do a 1 second prime.

Also, shoot some starter fluid in the throttle body and then try starting it and see if it will run a few seconds.

Thanks. I'll try this. When I rmove the fuel pressure gauge, some fuel comes out, but should there be a pretty good stream when the fuel pump is running?

 

[dirtdrdave]

Fuel pressure and fuel flow are step one in an EFI trouble shooting guide.

Try fuel into bucket mentioned above. How old is the gas? How is the filter?

Thanks. Gas is new. Replaced filter when this happened, did not help.

 

[dirtdrdave]

If your sure there is gas, the short piece of hose in the tank can rupture sending a tiny bit of fuel but not enough pressure to the rail. If that is your problem be sure to use fuel hose rated for fi and submersion.

Thanks. Something to look at. The tank came from BC Broncos with the fuel pump installed. I would think the correct tubing was used. I suspect that I am going to have to drop the tank.

Does anyone think the fuel pressure regulator could be the issue?

 

[jhill52]

If you shoot fuel into a bucket you should get a strong stream. Try it first at the tank outlet. Also check voltage at the pump.

 

[DirtDonk]

If you disconnect the vacuum line from the regulator no gas should come out. If it does then you have a ruptured regulator and need to replace it.
If you pull the pressure gauge then as far as I know you should get a large stream of gas when you turn the pump on.
When you turn the key to on the pump should only run for a few seconds at the most. Usually only about two seconds. If it continues to run then you have a computer problem.

Pressure regulators can fail, pumps can fail and yes the fuel line in the tank can occasionally fail as well. Luckily it has not happened very often, but it's often enough for it to be something to check if nothing else pans out.

How long was it sitting? Pump that has been used slightly and then left to sit for an extended period of time is often a bad thing. Modern pumps with modern gas seem to fail at a very high rate these days.

 

[dirtdrdave]

If you disconnect the vacuum line from the regulator no gas should come out. If it does then you have a ruptured regulator and need to replace it.
If you pull the pressure gauge then as far as I know you should get a large stream of gas when you turn the pump on.
When you turn the key to on the pump should only run for a few seconds at the most. Usually only about two seconds. If it continues to run then you have a computer problem.

Pressure regulators can fail, pumps can fail and yes the fuel line in the tank can occasionally fail as well. Luckily it has not happened very often, but it's often enough for it to be something to check if nothing else pans out.

How long was it sitting? Pump that has been used slightly and then left to sit for an extended period of time is often a bad thing. Modern pumps with modern gas seem to fail at a very high rate these days.

Thanks all. When I pull the vacuum line on the regulator no gas comes out. I was just hoping it was that because that is easy!
It was sitting for three years. It seemed to run well at first, but my suspicion is that the pump is partially functioning. Was hoping not to drain and drop the tank!
I will also check voltage at the pump.

 

[rjrobin2002]

It should be a steady flow out the fuel hose while the pump is running. About like a good adult piss stream, not an old man drizzle.

 

[dirtdrdave]

It should be a steady flow out the fuel hose while the pump is running. About like a good adult piss stream, not an old man drizzle.

I disconnected the fuel line at the fuel rail. When I turn the key on the fuel pump runs for about 2 seconds (which is what I remember it doing when it ran). I have to turn the key on and off about 4 times before I get any fuel. It then does spit out some fuel with a pretty good stream (not an old man drizzle) for two seconds. But it doesn't seem like that much. Normally the truck would start instantly. It doesn't seem like I should have to turn the key on and off 4 times to see fuel.
Does that seem right?

 

[SC74]

Sounds like you are getting air into your fuel system somehow and having to re-prime it. Did you try to re connect the fuel line, prime it 4-5 times, and then try to crank to see if it would start and continue to run?
What fuel filter do you have? I tried to run a spin on filter and it gave me a fit with priming.

 

[lars]

Does the Painless harness have a diagnostic connector like an OEM harness does?

Like this:

 

[lars]

If it does, you can short pin 6 to ground and with the key on the pump will run continuously. Makes checking pump function easier, compared to turning the key on/off constantly. Disconnect the line at the rail, run into bucket. With the line disconnected you should get around 1/2 gallon per minute or more.

 

[dirtdrdave]

Sounds like you are getting air into your fuel system somehow and having to re-prime it. Did you try to re connect the fuel line, prime it 4-5 times, and then try to crank to see if it would start and continue to run?
What fuel filter do you have? I tried to run a spin on filter and it gave me a fit with priming.

I did. It will run for a few seconds roughly then stall.

 

[dirtdrdave]

If it does, you can short pin 6 to ground and with the key on the pump will run continuously. Makes checking pump function easier, compared to turning the key on/off constantly. Disconnect the line at the rail, run into bucket. With the line disconnected you should get around 1/2 gallon per minute or more.

My rjm harness has that connector. That is good to know, I will try that.

Forgot to include, that I changed the fuel filter during this and it didn't help. Not sure exactly which filter, but it is threaded.

thanks

 

[EPB72]

My rjm harness has that connector. That is good to know, I will try that.

Forgot to include, that I changed the fuel filter during this and it didn't help. Not sure exactly which filter, but it is threaded.

thanks

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 ....

 

[rjrobin2002]

Pull your pump and see if some hose or something is disconnected or partially clogged.

 

[dirtdrdave]

My rjm harness has that connector. That is good to know, I will try that.

Forgot to include, that I changed the fuel filter during this and it didn't help. Not sure exactly which filter, but it is threaded.

thanks

Thanks everyone.

OK, so I grounded pin 6 to run the fuel pump continously. I get a very good stream at the fuel rail. Certainly in the 1/2 gallon/minute range as everyone suggests. I also pulled some of the injectors and get good flow at the outlets for the injectors. 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? The fuel pressure gauge still doesn't read anything when I hook it all back up.

EPB72, I am a little confused about how to dead head the pump as you suggest, but if I don't get return through the return line (I assume because motor not running with regulator in place as I mention above?) aren't I effectively doing that? Still no pressure reading.


Glad I didn't drop the fuel tank.