First of all, I already changed my fuel filter, spark plugs, pcv valve, distributor cap and rotor and throttle position sensor. I brought my car to a mechanic because at anything under like 3500 rpm the car had no power and was extremely lean. It was almost normal at WOT but something was missing and occasionally when I let off the gas after romping on it hard, it would backfire once really loud. I took it to the mechanic and he said my fuel pressure was all over the place and it was at 22psi. He set it back at 45(i have and adjustable fuel pressure regulator) and he said it was probly either the fuel pump or the brand new regulator I just put in was bad. How can I tell if it is the fuel pump or the regulator? I think it might be the fuel pump just because it feels like its getting no gas. HELP!

 

If you got more than 80k on it its prolly the fuel pump. I have never heard of a bad pressure reg. but I guess its possible. If you want to eliminate it as a problem just make sure that you put the metal coin lookin thing in when you installed the afpr. and if you want more piece of mind replace the diaphram in there as well. those are the only two things that can go wrong in there. but If you need a fuel pump I would strongly suggest going through summit. buy one of there fuel pumps in the mustang 5.0/4.6 section they are not exclusivly for mustangs they are just good walbro pumps for in tank use. I just installed one a few weeks ago. and it works great. The hardest part is to get the tank out. just make sure its close to empty when you do it. and dont even try to be careful just grab it, twist, pull and bend the hell out of that filler neck, its the only way to get it out. there pretty strong too and its really easy to bend back into place once you get it back in. well good luck with it.