2004 3.8L V6 Very High Fuel Pressure?

SVT232V6

Member
Our 04 V6 has very high fuel pressure and we can’t seem to figure out what’s going on. Car has a new fuel pump and module assembly installed by the previous owner. I replaced the spark plugs, plug wires and fuel filter as part routine maintenance. Fuel pressure on cold start up is ~39 psi. Fuel pressure increases after car has been running for a while. Also seems to increase when off the throttle. Tonight fuel pressure was still high(~57psi) even when accelerating on the highway at 55mph. Measuring fuel pressure both electronically with my BlueDriver OBD2 scanner and it’s roughly the same as with a mechanical gauge(at the time was around 55psi). I dropped the tank today and found no open or damaged wires at/in the tank. Any help would be greatly appreciated! There are no codes.
 

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6 Shooter

Well-Known Member
Check your messages for one I sent you. The answer is there. Just ask and find an SCT dealer in your area.
 

SVT232V6

Member
Check your messages for one I sent you. The answer is there. Just ask and find an SCT dealer in your area.

Regarding the fuel tables? There are no SCT Dealers in Hawaii, at least not on my island. Not even a dyno. Is there another way to remap the fuel tables? Can it be done through a scanner or laptop/OBD2 cable combo like VWs and VAG-COM?
 

SVT232V6

Member
of if not, what about a mail order tune with the correction?

If I could get a tune mailed to me, that’d be great. I don’t have an SCT Tuner though. I do have a laptop and can buy an OBD2 cable if anything to try and reflash the PCM.
 

6 Shooter

Well-Known Member
Contact VMP Tuning in Florida and ask them IF you provide the returnless pump value files, would they reflash your PCM or make the changes and send you the file. I can contact Justin and provide him with the numbers.
 

6 Shooter

Well-Known Member
In the Ford tune for returnless fuel systems, there are about 10 tables and files that control fuel pressure, testing fuel pressure, when to adjust the pressure when it deviates from 40 psi, how long to wait before beginning to adjust fuel pressure and by how much, a voltage table, fuel pump flow rates, plus proportional, integral, and derivative settings that cause the fuel pressures to change at the instant the the throttle changes. Those pressures are called desired pressure drop across the injectors, can be data logged, pressure can be read on a gauge at the fuel rail, and must rise when the throttle is increased and decrease when the throttle is decreased. Lousy numbers in the value files or other tables do not control fuel rail pressures very well, such as high spikes and pressure drops into the high 20s. Ideally, the pressures in the V6 Mustang should be 40, plus or minus 2 in throttle settings up to mid-range. Higher than mid range should cause pressures to head toward 50. At WOT, pressures should hit 60. On throttle off decel, pressures should drop down into the 35 or a bit lower range.
 

Serpent

Active Member
that is some great information. thanks for posting that. you sir are on a different plane than the rest of us!!!
 

Sam36

Active Member
In the Ford tune for returnless fuel systems, there are about 10 tables and files that control fuel pressure, testing fuel pressure, when to adjust the pressure when it deviates from 40 psi, how long to wait before beginning to adjust fuel pressure and by how much, a voltage table, fuel pump flow rates, plus proportional, integral, and derivative settings that cause the fuel pressures to change at the instant the the throttle changes. Those pressures are called desired pressure drop across the injectors, can be data logged, pressure can be read on a gauge at the fuel rail, and must rise when the throttle is increased and decrease when the throttle is decreased. Lousy numbers in the value files or other tables do not control fuel rail pressures very well, such as high spikes and pressure drops into the high 20s. Ideally, the pressures in the V6 Mustang should be 40, plus or minus 2 in throttle settings up to mid-range. Higher than mid range should cause pressures to head toward 50. At WOT, pressures should hit 60. On throttle off decel, pressures should drop down into the 35 or a bit lower range.

Yea I follow that... but there is no mention of him running a custom tune? Or is the stock Ford tune just bad from the factory? And what year mustangs were returnless?
 

SVT232V6

Member
The car in question is a bone stock 2004 3.8L V6 with 176,400 miles on the odometer. Girlfriend bought it with her 2018 tax returns as a project car. While the car was idling one day we noticed the exhaust popping sound. I thought it sounded odd and started running some checks and also noticed the fuel pump whine was quite audible and checked the fuel pressure on my scanner and it was 60+ psi at idle. External information sources stated that fuel pressure should be right at 40psi or so. At times the fuel pressure goes up to 80 psi even, at idle. Usually if the pressure is high at idle, it’ll go down to between 37-41 psi while driving on the highway at 55 MPH. Lift off throttle pressure increases steadily starting at 40 and rises into the high 60s. I’ve verified via mechanical gauge that fuel pressure was indeed ~55 psi when the scanner was showing 57 psi. I’ve tried switching the Fuel Rail Pressure Sensor with a known good one from both of our other Mustangs and there was no change in pressure readings. I dropped the tank to visually inspect the wires and couldn’t see anything obvious that stood out. Pin 63 voltage at the PCM matched the RED/PNK wire voltage at the FRPS. If there is something else telling the PCM to increase the pressure, or any other tests to run, I’m open to suggestions.
 

6 Shooter

Well-Known Member
Yea I follow that... but there is no mention of him running a custom tune? Or is the stock Ford tune just bad from the factory? And what year mustangs were returnless?

To my knowledge, the returnless fuel systems began in 1999. Further, the stock Ford tunes for the V-6, GTs, and the Cobra are all of poor quality from Ford for at least 6-7 years or longer. Have studied and compared each of these and their various returnless fuel pump settings and even tested each of them on my own car. Have a friend who is a grand master Ford tuner and he was able to experiment and find an improved set of value files after tuning a thousand high performance Ford cars while trying to control A/F ratios with 600+ rear wheel HP Mustangs. Have also tested his recommended settings on about 15 cars (V6s, Fiesta, GTs) myself and can consistently get the rail pressures to stay at 40 psi with a deviation of plus or minus 2 psi as shown with hundreds of data logs.
 
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