Slow Fuel Pressure


New Member
Apr 24, 2021
Iowa City
I have a stock '95 Mustang GT. Recently it started to feel down on power. While doing a fuel pressure test, I noticed that the needle on the guage was moving very slowly and eventually stopped at 32 to 34 psi at idle with no change when the motor is revved. It seems as though the car is struggling to build fuel pressure. Any ideas what could cause this? I couldn't find any fuel leaks while doing the pressure test. The system also held pressure when the car was off. As of May 2021 the car got a brand new 190lph Walbro pump, and brand new Wix filter. When changing the pump I inspected inside the tank for debris and it was clean. The car has also never been ran much bellow 1/4 tank since the pump was replaced. Any help is appreciated.
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Assuming the vacuum line is hooked up to the regulator, that’s pretty normal pressure. If the engine isn’t really under load then the pressure won’t move much when you rev it. Only way to check is to monitor pressure when you’re driving and you floor the gas. It should jump to around 39ish.

I’d put a timing light on it with the spout disconnected and see where it’s at as well.
You're right, the end pressure seems okay if not maybe a touch low. I'm currently more perplexed by the fact that the engine had to run for around three to five minutes before the guage read above 30 psi
Update: Using a different fuel pressure test gage with the "old" filter, I got immediate and consistent reading of 30psi at idle with vacuum hose on and 38psi with it off. At this point, filter doesn't appear to be the issue. I changed it anyway just to be sure, and the readings with the new filter were identical. One thing I did notice is when the windows are up, and the vent is on, I can smell gas fumes. It's not very strong, and it goes away eventually.
I'm completely stumped at why the car feels like it has 10 to 15 less horsepower. As always, any help is extremely appreciated