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I have a 1994 Mustang V6 and I just put in a new remanufactured engine. It has about 600 miles on the engine 180,000 miles on the body. The fuel filter got changed less than a year ago, I checked the fuel pressure at the fuel rails and got 30 psi which is what the book says it should be. I changed the upstream Oxygen sensors and got my exhaust system checked to see if I had a plugged cat after i blew the head gasket. I pulled the codes and got codes for both banks of the engine running lean but no other codes. I also used a stethoscope and checked all the injectors to make sure they are fireing. I also checked the vaccume line and that is up to par with what the book suggests. Im not sure what else to check so anyhelp or ideas would be greatly appreciated. The biggest problem i have with it is when i go to take off it just wont really go sometimes, it lags for a couple seconds but it doesnt go and it doesnt rev up really high either before it goes. Thank you guys, i love this web site.
 

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What does your fuel pressure do when you rev the motor? Your fuel pressure should read 32 psi at idle and if you remove and plug the vacuum line to the fuel pressure regulator, the pressure should increase to right around 40 psi.

If it doesn't, I would see if your regulator diaphram has failed. It sounds to me like you aren't getting any pressure when the fuel demand goes up.
 

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When I rev up the fuel pressure drops to about maybe 10-15 psi then jumps back up to normal. Does that help at all?
 

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That tells me that you either have a fuel pump or regulator issue.

When you rev the engine from idle, as soon as the vacuum goes away, the fuel pressure should go to 40 psi and stay there until vacuum is pulled on the regulator diaphram again.

Are you sure that your fuel filter isn't damaged or clogged?

How many miles on the car?

The fuel pump sock in the fuel tank could be gummed up, but that isn't likely.
 

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Discussion Starter #5
If I remove the vaccume it does jump to 40psi, I will probably just replace the fuel filter anyways since it isnt that expensive. The engine right now only has about 600 miles on it but it sat for about a year and a half as I was getting the money to buy the new engine and then putting it in. Thanks for all your help thus far
 

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Does anyone think that it could be the fuel pressure regulator?
Since you said the car sat for 1 1/2 years, I am thinking it is probably the fuel filter is gummed up and if that doesn't totally fix it, you may have to drop the fuel tank and replace the sock filter to your fuel pump.

Gas will varnish up if it sits for months or years in a fuel tank. Replace the filter first and if the makes it better, then you may be okay. For a car that sat that long and is that old, it might not be a bad idea to drop the tank and get rid of the old fuel if you haven't already. Start with fresh 93 octane fuel and then work from there.
 

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I got rid of the old fuel already but next time I fill up will get a high octane fuel. I just replaced the fuel filter today and got a healthy amount of fuel in the face lol but after test driving it still has the same problem so I will be replacing the sock filter. I noticed today that the more gas I try to give it before I let off the clutch the longer the hesitation is? Sounds like a clog to me, usually the more you try to push down a small hole the longer it takes. I hope the sock filter is the problem but I will post a when I find out, thanks a bunch.
 

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Well I changed out the sock filter/strainer but it didn't help it, I am going to change out my Throttle position sensor tomorrow. I will post tomorrow if it works
 

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Throttle position sensor did nothing, i'm not sure what i should check now? If it was a bad pump i would think that the pressure wouldnt necessarily drop it just would get high enough when i pushed on the throttle. Could it be my pressure regulator?
 
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