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I’m ready to shoot this hoss.
Started running rough / hard to start two weeks ago on long trip. Had several misfire codes, which were resolved with help of dealer…replaced all cops and plugs, and carbon vacuum. Dealer said intake was full of carbon. Ran fuel cleaner through as well. Still hard to start…requires 4-6 cranks before it will kick over, then seems to run fine. No more codes, but I am virtually convinced it is fuel pressure problrm.
After reading thru several 4.6 threads, did a FPDM voltage test…was at 12.45 volts, so, per the Ford manual (anything more than 10.5 volts, replace FPDM) I replaced Fuel Pump Drive Module with same part XR3F-9D372-AE. But, had to use a salvaged FPDM because all Ford dealers are out of new ones! Also replaced Fuel Rail Pressure Sensor with new one (3R3E-9F972-AA) just in case. Engine kicked right over at cold start, great acceleration, ran great for a day. Next morning, same cold start problem: 4-6 cranks before kicking over. But no Service Engine light/codes whatsoever.
I then did fuel pressure checks: key on: 22psi; idle: 38 psi; throttle 34-38 psi (actually jumped down at wot): 5 minutes after cut off 34psi first test, 42psi second test, but pressure was holding well on both teats. Idle psi seems ok (manual says it should be 35-50 at idle), but key on and throttle readings made me think it must be fuel pump. However, these checks apparently are useless because I then went back and checked FPDM and voltage was back to 12.45. Am I burning out FPDMs or what???? And if so, what is doing this???? Or just a fuel pump going bad.
Would greatly appreciate advice….I am at my wits end.
 

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I hope this does not come across wrong. But I get the sense that you do not understand how the FPDM works. Nor do I get the sense that you understand the results of the fuel pressure tests and what are good numbers vs bad. Please realize that when measuring fuel pressure, the numbers will be different if measured atomspheric verses intake referenced (DELTA).

How are you measuring fuel pressure and what is the engine doing at the time?

I am not certain from this post that you even have a fuel pressure problem.

Question. Have you check the vacuum reference line from the fuel pressure sensor to the intake manifold? Is it connected and leak free?

Do you have access to an ODB2 scanner to monitor operational data?

Trouble shooting this problem will be so much easier with an ODB2 scanner. For the cost of a new FPDM.......

A couple of tricks to try. Cycle the key on/off/on/off several times without starting. Do you hear the fuel pump running with each cycle? Does this improve starting?

Next try holding the throttle half way open. Does this improve starting?
 
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