01 GT lost of fuel pressure after OP Temp

[hiXis]

Having an issue with fuel pressure after the engine is warmed and going into WOT a few times. Once OP temp is up and WOT is achieved, Autotap shows fuel psi to go from about 40 psi to 10-20 psi. Turning the key off mid flight does at times bring the fuel psi back to 40 psi but as soon as the throttle is hit again (normal acceleration) the fuel pressure goes back to 10-20 psi.

After reading more on how these return-less fuel systems work, I'm starting to understand somewhat on how things operate in junction with each other, but being still totally new to the troubleshooting concept of the entire idea, I'm looking for some straight up trouble shooting info. (CCRM,FRPS,FPDM ect who would know unless they had these problems.. ffs most part dealers don't know what this is!)

-FRPS has plenty vacuum unplugging the vac line from the sensor.
-FRPS unplugged the vac line doesn't raise any idle.
-FRPS unplugging the electrical sensor, itself DOES raise idle.
(for what it might be worth putting a vacuum pump on the FRPS vacuum inlet at any lbs doesn't raise any idle speed/ECU funtion)

-FPDM is getting 12 volts and the FP is priming on key-ON
-FPDM back probed on pin 3 and pin 10 (going to fuel pump) is getting 7.65 DC volts at idle (not 12?)
-FPDM ohm to ECU pin 40 shows no broken wire.

I'm new to troubleshooting electrical problems on this type of application, and need some help to understand and learn quickly why I have a lose of fuel pressure when operating temp is achieved. We learn as things break, not by tearing a fender apart to find whats inside

 

[wmburns]

Are there any DTC codes? If so, they need to be posted.

Normally the PCM runs rich until the motor is at full operating temperature. This could be a problem with the ECT or it could be an issue with incorrect VREF voltage.

FPDM pin 3 and 10 do not read 12 volts because that is how the FPDM controls the FP output. If FPDM pins 3 and 10 did read 12 volts, the FP duty cycle would be 100%.

OBTW, disconnecting the FRPS vacuum line will not change the idle because of the feedback from the IAC. It will make the motor run rich at idle.

IMO you need a set of Ford workshop manuals, wiring diagrams, and PCM manual. The wiring diagrams will aid in understanding how the fuel system is put together. PM if interested in getting a copy for yourself.

 

[hiXis]

No DTC Codes found & no service engine light. Engine light does work as I've unplugged some key sensors yesterday just to test it.

Today I ran a data log with autotap until the problem happened, I was hoping I could upload it up here but it's an .atl extention. I can however write here any parameters both from engine warm to 45 minutes later when the fuel psi dropped to 10 psi. Ty again for the reply, in my quest for this problem I've seen your posts all around goggle for different things, so I know you have much knowledge in these cars & your time is appreciated.

Once "something" cools down (warm) the engine runs and performs GREAT, then back to a severe drop in fuel pressure after a good operating temp. I've not seen anyone with this same problem "searching the net" for answers.

 

[wmburns]

Tell us about what work was done the the fuel system. Have any mods been done that might allow the fuel lines to get hot?

This could also just be a case of a bad fuel pump. Fuel pump gets hot and cuts out. Possible for a car that has been setting for a long time.

What is the engine temperature as reported by the PCM right before this problem happens?

 

[hiXis]

Well before going into the tank, I used a hand pump sprayer injecting fuel into the FR just to "check" if it was going to start & it did, ran it for a few minutes this way pumping the bottle to keep pressure checking all lights ects. That being said the first thing next was drop the tank to find the FP which was locked up solid, but had voltage. Changed it out with a stock pump along with a new fuel filter and fired the engine right up.

Ran 1103 records on autotap today, on record 694 fuel pressure spiked to 12psi then went normal (38-42psi). On record 754 -1103 it dropped to -10 to -20 psi & the operating temp was 194F.

STFT Bank 1 went from 0.8% to 32.8% (idle) 40 psi to 10.9 psi)(record 1 and record 1103)
STFT Bank 2 went from 0.0% to 32.8% (idle) 40 psi to 10.9 psi)(record 1 and record 1103)

Maf sensor (brand new) was 0.899 to 0.998 First & Last Record.. Would be more than happy to email you the datalog for playback

 

[wmburns]

Is the fuel pressure sensor intake vacuum reference line connected and leak free?

Have the alternator tested for excessive AC ripple.

Monitor LTFT instead of STFT's.

Have you crossed checked the PCM reported fuel pressure with an external gauge?

Need to know what the battery voltage and VREF voltage when this problem happens. The VREF between the FRPS BN/WH and GY/RD wire. VREF should be about 5 volts. Battery should be about 12-14 volts.

Does it make sense for the fuel pressure to be negative?

 

[hiXis]

Is the fuel pressure sensor intake vacuum reference line connected and leak free? Connected & leak free

Have the alternator tested for excessive AC ripple.
On the list


Monitor LTFT instead of STFT's.
LTFT Bank 1 -2.3% (40 psi) 17.2% (12.9 psi)
LTFT Bank 2 -4.7% (40 psi) 25% (12.9 psi)
(warm to hot)

Have you crossed checked the PCM reported fuel pressure with an external gauge? External showing 25-40 psi

Need to know what the battery voltage and VREF voltage when this problem happens. The VREF between the FRPS BN/WH and GY/RD wire. VREF should be about 5 volts. Battery should be about 12-14 volts. I'll check this one tomorrow after driving again

Does it make sense for the fuel pressure to be negative? My error in reporting.. it's 10-20 psi

 

[wmburns]

For the cross check of fuel pressure with an external gauge, I need to know how they relate to each other. For example, the PCM said X the gauge said Y under the same conditions.

As I understand it, a new fuel pump has been installed. Confirm that you have used the correct fuel pump for this application. The fuel pump must be able to deal with variable pulsed DC voltage that the FPDM uses to control pump output.

A fuel pump designed for constant voltage (return style) could overheat in a variable DC application (return-less).

Confirm if an upgraded fuel pump has been used. Sometimes if too large of a FP is used, the fuel pressure will spike under WOT. This causes the PCM to shut down the FP.

 

[Lugnuts]

+1 on the chance you have the wrong pump installed. Sounds like a constant voltage pump in the wrong application to me. You don't still have the part number you purchased do you? I would like to rule that out.

 

[hiXis]

Did some more research on the car and getting 2.7 volts on the FRPS which points to 40psi, also the VREF is 4.9 steady before the fuel pressure drop exists. I was to busy with work ect to run the car and get the results when the problem occurred but did see from my mobile a few questions.

Fuel pump I purchased was an airtex e2366, so in my question of "is that what's in the tank" I took the gf's car over to my shop and grabbed the box for it.. same number. I have the car on jack stands tonight and tomorrow the pump is coming out, being changed (1 year warranty) and while I'm inside I'm going to replace any fuel lines in the tank. I posted a .zip file on another forum containing the data logging using auto tap, pm me and I'll msg the link to dl it being there are no zip files here that can be posted.

One thing I get aggravated with is when searching problems on the net in a lot of forums, right when you have a thread that you may find the answer to, it's left dead to all (forums, web browsers ect). When I figure this one out it will be posted for the tech like you guys, or the simply problem chaser like myself.

 

[wmburns]

The Autozone web site indicates the Airtex E2366 is the stock replacement FP for a 99-04 MY Mustang. If you really don't mind dropping the tank, that's up to you. Seems just a little too soon given the information.

Do you know if the tune in the PCM is stock?

 

[hiXis]

Dropping the tank for 2 reason, one is to rule out they sold me a faulty pump by bringing it back and getting another one, and second is to replace the fuel line in the tank, and also check my work.

Tune is factory from my orig engine (bought the car new), altho I have SCT LiveWire, I've never had the car tuned yet other than the simple TC off, ERG off, Rear O2's off .410 (for speedo) ECT you do yourself. When I do get this fuel issue corrected it will get it's first tune.

 

[wmburns]

If the FRPS intake vacuum line is disconnected and the external gauge does not change, this is an important clue. It says that:

• The FRPS is bad (busted diaphragm for example).
• The vacuum line itself is not actually connected to the intake manifold, blocked, or leaks so bad as to have lost vacuum reference.
• There's an electrical issue with the FRPS return signal line (dirty/loose/bent/pushed pins).
• The PCM is bad and not reading the FRPS sensor changing.

IMO, this clue should not be ignored.

Without the vacuum reference line, the delta fuel pressure will be too high at idle (rich). For a NA application, the amount of fuel pressure error will decrease as the throttle is opened. This causes the PCM O2 feedback loop to constantly go from excessively rich to almost OK at WOT.

If you do decide to drop the tank, double check the electrical lines just under the pump hat. Sometimes the lines will get caught between the hat and gas tank. This could cause a weak electrical connection. Also as you have said, it's a good idea to look of leaks in all lines.

 

[hiXis]

Like to take a minute and thank the guys at Stangnet for the views/reads of this thread, and those who had no comments to address the problem at hand that may have confused things or made my search longer (no pun intended). Special thanks to wmburns for his write-ups here that made me look, learn and be more aware of some of the things on these Mustangs I, really had no idea was on them (sensors, checks, troubleshooting).

After dropping my fuel tank last night, I found my answer almost immediately. The car did sit up a few years while I finished paying a note on it, I had a lot of money tied up in the vehicle and didn't want to let it go. After an engine swap I changed the fuel pump & fuel filter, the problem arose a few weeks later with no fuel pressure due to the fact the FP socks (both) were full of rust. After the car ran 30-45 minutes, the pump was overheating dropping the reported autotap fuel pressure to about 10PSI. No engine light because the computer might have thought It was simply running out of gas. Had I had my meter hooked on pin 3 and 10 (at the time of the problem) on the FPDM I might have seen a duty cycle issue. I did drain the tank, install a new FP and filter, but didn't clean the tank completely after it sitting so long. My last guess was the FP. After 2 weeks (after work) problem solving, the simple answer is above being, FP was getting over heated after operating temp, shutting down and causing my entire issue. (BTW I used CLR as seen on TV to remove well over 90% of all rust in the tank before putting it all back together)

I hope this thread helps someone down the line that has to store a vehicle for some period of time, and I once again want to thank you guys for the input as it was appreciated!

 

[wmburns]

Outstanding. I wish more ppl would take the time to follow-up their threads with the final results.