My 94 mustang v6 manual has a really bad hesitation problem when I go to take off. I only codes that have come up from the OBD2 scanner is saying that both sides are running lean. I have checked my fuel pressure, at idle reads 32, removing the vacuum reads about 40psi, but when i rev the motor my fuel pressure drops dramatically before it comes back to normal which is causing my hesitation. I have replaced the fuel filter, sock filter/strainer on the fuel pump, the throttle position sensor, and the upstream o2 sensors. I have noticed that if i apply throttle slowly it doesn't die down very much just when i apply a lot of it quickly, also when i replaced the sock filter/strainer on the fuel pump it has gotten worse my guess being because the new filter lets less fuel through and filters more. I don't know what else to check and i can't just keep throwing parts at it and waste my money, please help. Thanks
Thanks for your quick reply. I'm getting correct fuel pressure at idle but not when i push on the throttle, it drops for a couple seconds then comes back up to proper idle pressure. Could my fuel pump still be the problem even though i am getting correct fuel pressure at idle and idle without vacuum? I should also mention that i have checked my vacuum lines with a gauge and checked them for cracks or leaks. On top of that i have checked all injectors with a stethoscope and all of them sound like they are firing. Thanks for your help
I forgot to add that i have checked all my pressure levels with the ones with the book, the fuel pressure and the vacuum lines meet the specified pressures from the book
if the fuel pump is failing, it could still provide the correct pressure at an idle. the reason you rev the engine while checking pressure is to put a load on the pump and see if the pump can handle the demand. the pressure should hold steady; if not you have a problem. you may want to look into the fuel pressure regulator also.
just to be 100% sure it's not a vacuum leak, i would spray some intake/brake cleaner around all the vacuum lines and intake clamps/connections. if the engine revs up thenyou have a leak. if it were a vacuum leak, it would have to be a vacuum leak that would affect both banks, since you have both banks running lean.
Is there anyways i could test the fuel pressure regulator? I checked prices on both already and the fuel pump is a little over $100 and the fuel pressure regulator is just over $50, i have already bought and replaced a couple unneeded parts and i really hope I don't do it agian. Is there anyways to narrow it down?
Is there anyways i could test the fuel pressure regulator? I checked prices on both already and the fuel pump is a little over $100 and the fuel pressure regulator is just over $50, i have already bought and replaced a couple unneeded parts and i really hope I don't do it agian. Is there anyways to narrow it down?
im not sure...if you have a dvom, you may be able to check the resistance of the fuel pressure regulator, if you can find out how many ohms the spec is. i would check a shop manual or a haynes manual for that info.
someone else will be able to tell you for sure if there is a way to test the fuel pressure regulator. if you can test it, and it turns out good, my bet is that the fuel pump is failing.
There is no electrical line to the FPR only fuel lines and a vacuum hose so i cant test it with a DVOM. I did some research and found that the test is to remove the vacuum line and if the pressure climbs then its working which it did to also if the diaphram in the FPR is leaking then the vacuum would suck raw fuel that passes through it into the intake and to test that you just remove the vacuum line and check for fuel which there wasnt any. It looks like i will be dropping the fuel tank again and replacing the fuel pump unless anyone has any other advice. Thank you for your helping, i ruled the fuel pump out because of the correct fuel pressure reading so thanks for your advice.
1994 Mustang acelleration hesitation 
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