Mustang Returnless Fuel System Problem

[2000AtlanticGT]

Need some help from you Ford returnless fuel system experts.

I am not getting voltage from the FPDM (fuel pump driver module) to the fuel pumps. I have a wiring upgrade done that includes an 8 ga power wire running from the battery to a relay in the trunk that provides power to the FPDM. At the same time that was completed a Fore hat assembly with twin Ford GT fuel pumps were installed. I had the car tuned with this set-up at MPH just 3-4 weeks ago. Also, I upgraded the FPDM to a zone 5 stage 2 FPDM to be able to take the extra load of the new pumps. All was well for about 2 weeks.

I noticed that there was a hesitation (for a fraction of a second the engine shut off then came back on) on high rpm, fast shifts from 2-3rd gear. MPH told me it was in the tune and could fix it. The car had been sitting for 4-5 days, I went to move it before I pulled the chip out to send to MPH and the car would not start. I had no fuel pressure and I could not here the pumps run when I cycled the key.

I checked all of the new wiring upgrade and all is good. I have power on all pins of the relay when the key is cycled, voltage going to the FPDM. I swapped in my stock FPDM and still no change so the FPDM should be ok. Checked the stock fuel pump fuse, it looked questionable, swapped it and nothing changed. I have voltage going to and out of the fuel inertia switch so that should not be an issue. I even swapped in an extra FRPS (fuel rail pressure sensor) that I had in the attic to make sure the hesitiation (fuel spikes) had not taken it out but it did not fix the problem either.

Any ideas what I should look at next? My Haynes manual is worthless, it does not show any of the wiring details for the FPDM. It just shows the inertia switch and then the fuel pumps.

[BenS]

stupid question time, but have you tried cycling the inertia switch? The one on my truck got tripped one day when there was a guy using a concrete pounder. The thing is the switch was in the "up" position (like it was not tripped). It only started after I stuck my pocketknife under the button and popped it up, and then pressing it back down.

You probably don't have to worry about that since you see power on both sides, but it would be easy to check.

[MeanMike]

Pull your chip out and see if the fuel pump comes on. Maybe it's got some corosion on the connections. That can cause the computer to do stupid stuff.

Other than that you'll need some good wiring diagrams to check it out. Any ford dealer should be able to print them out for you. It's a fairly simple circuit. Basically just an op-amp with the frequency signal from the ecu.

[LINELOCKSRUS]

lloyd & mike where are yall @ DoOds

[2000AtlanticGT]

stupid question time, but have you tried cycling the inertia switch?

I messed with it a little but it was depressed all the way down and since I had voltage going through it I went on to the FPDM. The fuel inertia switch is pre FPDM and I have power going to the FPDM on that circuit.


Pull your chip out and see if the fuel pump comes on. Maybe it's got some corosion on the connections. That can cause the computer to do stupid stuff.

I tried pulling the chip out and put it back in to make sure it was not lose but that did not change anything. I did not try it with the chip out, I will do that when I get back in the garage tomorrow.

Other than that you'll need some good wiring diagrams to check it out. Any ford dealer should be able to print them out for you. It's a fairly simple circuit. Basically just an op-amp with the frequency signal from the ecu.

Yeah, I suck at trouble shooting electrical problems. I did find a couple pieces of info today that shows the FPDM wiring and the fuel pump wiring. There is still more to it than this though because it is not showing the FRPS in that diagram. The spare FRPS that I tried was from the fuel rails that you gave me when I bought the Cobra fuel system from you. I am still wondering if I should try a new one, but before I do that I want to see how it falls in the fuel pump circuit. I know it has to tie into the circuit somehow limiting voltage based on the pressure readings.

http://www.vmptuning.com/downloads/wiring_diagrams/Mustang/01FPDMpin.jpg

http://www.vmptuning.com/downloads/wiring_diagrams/Mustang/00FPDMdia.jpg

[2000AtlanticGT]

On the FPDM plug pin 9 (FPDM power) I have 11.8 volts, but I am seeing 0 volts from pin 10 (fuel pump power). I have swapped between my new modified FPDM (been using it for a couple months), back to the stock one and still no power out of pin 10. There has to be something in the PCM circuit pins 1 or 7 that is telling it not to supply power to the fuel pumps.

I love this stuff....

[KJP]

If the fuel pressure sender is open circuit it may be telling the ECM that the fuel pressure is to high. The ECM will then not run the pump or run it slowly to bring the fuel pressure back down to the correct value. Check the wire coming out of the Pressure sender and check it at the computer. if it is near 5 volts the pressure sender is bad or has a bad ground connection.

Kevin

[2000AtlanticGT]

If the fuel pressure sender is open circuit it may be telling the ECM that the fuel pressure is to high. The ECM will then not run the pump or run it slowly to bring the fuel pressure back down to the correct value. Check the wire coming out of the Pressure sender and check it at the computer. if it is near 5 volts the pressure sender is bad or has a bad ground connection.

Kevin

Yeah, I need to get a wiring diagram showing the FRPS and how it ties into the ECM so I know which wires to check. Thanks for the advice, I will dig deeper into that tomorrow.

[MeanMike]

Yeah, I suck at trouble shooting electrical problems. I did find a couple pieces of info today that shows the FPDM wiring and the fuel pump wiring. There is still more to it than this though because it is not showing the FRPS in that diagram. The spare FRPS that I tried was from the fuel rails that you gave me when I bought the Cobra fuel system from you. I am still wondering if I should try a new one, but before I do that I want to see how it falls in the fuel pump circuit. I know it has to tie into the circuit somehow limiting voltage based on the pressure readings.


The fuel rail pressure sensor doesn't tie into the FPDM. It goes straight to the PCM.

The fpdm works as a big transistor. 12 volts/ high current comes ( pins 9,2) in to a switch with a wire from the ecu (low current pins 1,7) that turns the switch on and off at a certain duty cycle. The output from the "swtich/transistor" goes to the fuel pump (pins 3,10) at high current at the same frequency as the wire from the ecu.

If you've got 12 volts coming in and and nothing going out, either the fpdm is shot (you verified it wasn't) or the switching wire from the ecu is not sending anything out.


The FRPS goes straight to the computer. The basics of it is, there is a table in the ecu that looks at the FRPS voltage and give an output duty cycle to the FPDM. I'm not certian, but the pumps should come on even if the FRPS is shot or disconnected. So I doubt that is part of your problem.

I forgot all about selling you that fuel system stuff.

[2000AtlanticGT]

I tried pulling the chip out this morning before church and still no voltage to the pumps with it out.

So, sounds like I need to check the FRPS voltage to the ECU. I need to get a wiring diagram showing which wires connect the FRPS to the ECU because I want to check it at both ends, leaving the sensor and at the ECU. If that checks out ok, then I need to check the voltage coming out of the ECU to the FPDM going to pins 1 & 7.

Is there anything else it could be? If all of that checks out could it be an ECU problem?

Thanks for all the help.

[2000AtlanticGT]

Just for the heck of it I tried a 3rd FRPS (borrowed from a friend) and as expected it did nothing. I did get it to start with the original FRPS back in, which I have done a few times during all of this. It would idle, no fuel pressure showing on the gage and if you tapped the throttle in would try to die. Just enough fuel to let it idle. I unplugged the FRPS while it was idling and it tried to die and plugging it back in kept it running. Not very scientific but it appears to be functioning and communicating with the ECU.

I just need to get a wiring diagram and some specs for what the voltage from the FRPS to the ECU should be. Also need the same for the ECU to FPDM (pins 1,7). Actually I know what wires these are, just do not know what voltage it should be sending with the key on and car not running or at idle if I can get it to start again.

Is this something the dealer can give me? Any Ford techs on here help me find this info?

[2000AtlanticGT]

If you've got 12 volts coming in and and nothing going out, either the fpdm is shot (you verified it wasn't) or the switching wire from the ecu is not sending anything out.

I just checked and on pin 7 I am getting 6.6 volts when grounding to the FPDM ground, nothing on pin 1 on the same ground.

I have no idea what it should be on either of those wires. Need to find that out or get someone on here with a similar car to check and see what they are getting on these pins from the FPDM.

[MeanMike]

If you can get ahold of a sct programmer or diablosport predator or any kind of datalogger, it should tell you what you want to know. It would have fuel pressure (if any is there) and fuel pump duty cycle.

Delk could probably print out the diagrams you need.

Just an FYI. If it comes down to the ecu, you can't just swap them out like an older car. A new ecu has to be programmed to match your keys before it will let the car run. This is something that can only be done with an NGS star tester that either the dealer or Delk can do.

[2000AtlanticGT]

I took it to MPH today to have them look at it since they installed the pumps and tuned it for me a few weeks back. They could find nothing wrong in the wiring. They dropped the tank and pulled the pumps but all looked good. They took me out back and showed me everything pulled apart.

It looked like an FPDM problem to them so they tried yet a 3rd FPDM and the damn car started right up. They pulled the cover on my upgraded FPDM and the connection inside that goes to the fuel pumps were discolored. My stock FPDM which was only hooked up to test to see if I could get voltage to the pumps as a test had the same connections completely burnt in two.

They have had one other car do something similar, but they are not sure why. After discussing some options, I made the decision to convert the car to a return style fuel system to get rid of the FPDM all together. Lesson learned, should have done this the first time around but did not because of the extra expense. Converting is not cheap can tell you that!

[bigmike83]

I took it to MPH today to have them look at it since they installed the pumps and tuned it for me a few weeks back. They could find nothing wrong in the wiring. They dropped the tank and pulled the pumps but all looked good. They took me out back and showed me everything pulled apart.

It looked like an FPDM problem to them so they tried yet a 3rd FPDM and the damn car started right up. They pulled the cover on my upgraded FPDM and the connection inside that goes to the fuel pumps were discolored. My stock FPDM which was only hooked up to test to see if I could get voltage to the pumps as a test had the same connections completely burnt in two.

They have had one other car do something similar, but they are not sure why. After discussing some options, I made the decision to convert the car to a return style fuel system to get rid of the FPDM all together. Lesson learned, should have done this the first time around but did not because of the extra expense. Converting is not cheap can tell you that!


do you have all the stuff to convert it already?

[2000AtlanticGT]

do you have all the stuff to convert it already?

All of it was ordered today.

[bigmike83]

All of it was ordered today.

pm sent