No fuel pressure after engine swap

So i just swapped motors out of my 2006 mustang gt an dropped a 2010 4.6 3v in because my motor sent a rod an dropped a piston.. So the car has sat for maybe 6 months now with a dead battery... Long story short after having my motor dropped in everything hooked up, it will start an run an die out after hitting the gas... Had the fuel pressure checked which is running around 10 psi an drops to 0 after hitting the gas pedal.. But this is a brand new fuel pump i installed last year maybe a month before my motor took a dump.. An a check engine light did come on for fuel pressure regulator... How can a fuel pump go bad from just sitting for about 6 months.. My buddy is dead set on it being a fuel pump i just feel as if its not... Car does have comp cams stage 2 nsr bbk long tube headers xpipe jlt series 3 cai an a custom dyno tune.. Any help would be appreciated. An the only reason as to why i feel its not the fuel pump is, because same buddy told me my original fuel pump was bad an after i swapped them out it didn't fix my no start i was having last year... Was my spark plugs all along then a month later it sent a rod an dropped a piston..

The fuel pump is easy to remove and test so why not try that? Perhaps the fuel pump filter sock is clogged up.

Dino Dino Bambino said:

The fuel pump is easy to remove and test so why not try that? Perhaps the fuel pump filter sock is clogged up.

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Already tested he said only has 10 psi, an drops to 0 when trying to rev it, an dies out if you don't keep it to the floor.. An no the fuel pump filter is clean no debris not clogged it an yes i hear the fuel pump kick on as well..

Then there can be only two possible causes; either a bad fuel pump or a bad fuel pressure regulator.
You could test the fuel pump to find out how much fuel it flows. I believe it should be 110lph or 1.83 liters per minute.

Third problem is always wiring. Suggest rechecking all connections. Other concern is only 10 psi. Should be higher (35 - 45 minimum). Dropping to zero appears to point to a pressure regulation issue. Something else to check is the FPDM/Shut off switch in the trunk and the fuel pump relay in the engine bay. Connections can loosen/corrode over time. And check/disconnect/clean grounds for associated systems where you find them. I've had more problems with bad grounds than I care to think about... There's a good high-level write up on Mustang fuel systems from AM here: https://www.americanmuscle.com/return-and-returnless-fuel-systems-explained.html

Also, here is a wiring diagram for a 4.6L 3V that illustrates the layout and connections.

Should have 39 psi fuel pressure with the key on. Engine running or not. The fuel pump or the fuel pressure sensor on the fuel rail could be bad. The FPDM in the trunk is also a suspect and bad wiring connections can cause this as well. This is where a data log from a X3 or X4 would be a great help. It would show you exactly what is wrong.
How is your buddy checking the fuel pressure?
Did you install the engine with the 2006 intake manifold or the 2010?

So! What is going on with your fuel system? Have you plugged into your OBDll port and looked at fuel rail pressure, fuel pump duty cycle, fuel pump voltage and a few other things? It’s right there to see and will sort out the problem quickly.

Midlife Crises said:

Should have 39 psi fuel pressure with the key on. Engine running or not. The fuel pump or the fuel pressure sensor on the fuel rail could be bad. The FPDM in the trunk is also a suspect and bad wiring connections can cause this as well. This is where a data log from a X3 or X4 would be a great help. It would show you exactly what is wrong.
How is your buddy checking the fuel pressure?
Did you install the engine with the 2006 intake manifold or the 2010?

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Wrong.
39psi is base rail pressure.
You should have that with key on engine off.
Assuming you have 24”Hg of vacuum at idle you need to subtract the vacuum (negative pressure) from the equation.
1”Hg= 0.491psi
For our use this is close enough to 0.5 that we can say subtract 1 psi for every 2” Hg of vacuum.

For my example above of 24”Hg you would need to subtract 12psi so you should only see 27psi at idle.

If the car has forced induction fuel pressure will increase 1psi for every pound of boost. So if you are running at 10psi of boost you should see 49psi of fuel pressure.

keep in mind that not all tuners maintain the stock 39 psi base pressure.

I believe that the first Kenne Bell tunes increased base pressure to somewhere around 50 psi.

As already mentioned the Fuel Pump Driver Module (FPDM) located in the spare tire well and the fuel rail pressure sensor on the drivers side rail are 2 other possibilities.

My first test would be key on engine off.
If you don’t have 39 psi then the pump shouldn’t stop running. If it stops then I would start looking at the fuel rail pressure sensor and go from there.

Kind of an oblivious question, but did you check the fuel filter under the car along with the filter sock?

WRONG
Interesting. Setting here looking at data logs for my engine when I was playing with the fuel system. Key on, engine off fuel rail is 39 psi give or take a few 10ths. Warm engine idling at 820 rpm fuel rail pressure is still 39 give or take a few 10ths. There is no vacuum or manifold pressure listed in the PID list but my boost gauge says I’m at 28”. At that time I was evaluating the pumps so I also recorded fuel pump duty cycle 0.17% and fuel pump voltage 4.99V.
Yes these numbers are different when the engine is under load and one hell of a lot different at 6,800 and 15# boost but that doesn’t really help the OP with zero fuel pressure. All he has to do is plug into the OBDII port and look at a few numbers and the fuel system will tell on itself.

You were measuring a delta pressure or inferred inj pressure drop pid then. Actual pressure is lower under vacuum. Hence why the frps has a vac line running to it.

I understand what your saying, I just don’t have a chart showing anything other than a spike going below 39 psi and nothing stabilizing down there.

On my 2010 auto (with M90 blower) I get 50 psi fuel rail pressure with key on, eng off. And 40 psi with eng on. 40 psi regardless of rpm. This is with an aeroforce gauge plugged into obd port. FPDC is 40% at idle, 80% at 6 krpm, blower on, gas pedal mashed.

I had problems a few years back. Fine when out of boost, but when trying to get into boost, it would gag, and rail pressure dropped like a rock down to 5 psi..and FPDC was almost maxed out. Turned out to be a clogged sock filter that goes on the bottom of the oem fuel pump.

That is pretty much what I see when driving around. Right around 39 psi idling and light driving. The duty cycle and pump voltage go up and down to maintain that. When the boost gauge climes above zero the fuel pressure climes with it along with the duty cycle and voltage. A problem I had was I could not pull above 4,000 rpm. Just like running out of fuel. Watching a log in real time I wiggled the wire connection on the fuel hat and and bam, duty cycle dropped from .4 to .17 when the second fuel pump came on. Repaired the connector and the problem was solved.

My actual fuel pressure with key on is 39 psi. Once I start the car it actual pressure drops to just about 20-21. When I get on it I've seen as high as 52 psi of actual pressure. This is all while maintaining a pretty constant 39 psi relative to manifold pressure. You have sudden dips and spikes when getting on and off the throttle abruptly but it should just be for a split second as the pumps either catch up or the pressure drops off.

Repaired the connector and the problem was solved... Hmmm, wiring problem.

I don't usually prognosticate but A really important lesson I learned many decades ago was one of the admonishments from our teachers that when chasing electrical problems never forget the wiring itself and connectors. In many cases you'll find that the really weird problems will boil down to opens, shorts/grounds, and resistance/ground issues where connectors appear to be connected but may be intermittent. The trick is understanding the circuit well enough to half-step until you can isolate the problem down to an area and then check everything in the circuit (or figure out a way to test/eliminate that area).

Not sure how many others have chased electrical gremlins but I know I've spent weeks chasing what turned out to be bad/poor grounds and intermittent electrical connector issues. These days I double-check anything I take apart electrically when it's reconnected and check it w/a volt/ohm meter where appropriate. Also, instead of using those cheap wire taps or crimp connectors I'll solder any wires I cut and heat-shrink and/or install full two-piece weather connections to cut down the possibility of a bad connection/corrosion. Probably anal but have learned over the years anything you touch you can introduce a problem to. Sorry for the diatribe but it may help someone else avoid chasing electrical gremlins in the future.