So I just got the car it’s said to have a 255 walbro and it has what I think is a Holley adjustable fuel regulator I have set the idle fuel pressure with vacuum off at 40 and it seems to stay but when the car acts up I can turn it off for a min and back on the fuel pressure will go back up at idle but if you drive it’ll go right back to what it was doingOff the top of my head these are some possible issues the car has (could be one or multiple): a failing fuel pump, the "S" hose between the fuel pump and the hanger has a tear in it (they rot out over time), plugged strainer/sock on the suction of the pump, plugged fuel filter, or a failing fuel pressure regulator.
Is the fuel pump the original one? If it was replaced when was this done and what brand and flow rate?
When was the last time you changed the fuel filter?
Is the pressure regulator on the fuel rail the original? If its been replaced what brand is it?
It does have a celCan you see if the car is generating any codes? CEL light does not have to come on for there to be codes.
Got the codes 23,31,67,81,82,85,84Would suggest you pull the codes first and work through them. Some may be "permanent" in that if you have deleted things they will not clear. I'm curious if you have any related to the fuel pump circuit.
I got the tps in range it’s still dropping fuel pressure when driving I’m thinking filter or pump it only does it when it has been running for a minuteGo here for the codes:
EEC Codes - Figure Out What Your Fox Body Codes Are
The fox Mustang's EEC IV computer has two connectors for self-testing and located on the driver-side firewall. The large connector contains the self test output (STO) and ground (SIG RTN)....www.foxstang.com
LMR also has them:
The one that is suspect is this one:
23 - Throttle position signal out of specified range
You need to get that cleared first. Go here:
Mustang TPS Adjustment - 0.99v not necessary
EDIT: This post applies to 86-93 5.0 Mustangs. Seems to be a common myth, so lets sticky a thread explaining how the TPS works. Jrichker has provided the basic TPS guideline to follow. But here's a snip of the A9L GUFB which is the programming logic. Pay attention to the part highlighted...stangnet.com
After you get it in range either by adjustment or a new TPS clear the codes and then pull them again.
Replaced the filter today really dirty fuel coming out before the filter end the other side came out clean. didn’t fix my issue I didn’t read what you said until today I will try turning the pressure up and see what happens. Also I have what I think is 30lb injectors would that be to much injector. Also when the problem starts occurring the fuel pump gets real noisy making me believe it is the pump.See if you can do what Mr.Kelly suggests above. If you can sweep the pressure with the adjustable FPR then I would say the FPR is working as it should be. Check the vacuum line on the FPR for fuel as that is an indicator that the diaphragm is damaged and you can usually get rebuild kits for them. From there I would change the filter as that is cheap and easy. If the filter is still the stock style it will be a Motorcraft P/N FG-1060. It is located above the passenger side of the rear end in front of the fuel tank. The fittings on either end have some aweful clips that hold the lines on the quick connections of the filter housing.
LMR has a pretty good video on replacing them:
If this does not fix the issue then my next guess would be the pump so that means dropping the tank.
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