Fuel pressure drop at WOT

[Sonicblue_s197]

Last night I was out getting a log in and planned to go from 2000-6000 rpm. I went ahead and started the pull and around 4800 rpms I loose fuel pressure down to low 30s and even dippes into the 17 psi range and the car leaned out hard AFRs shot up into the 13s so I caught it and shut down right away. I drive home and the car was idling fine fuel pressure is set at 44 psi but just revving it up it would dip down to low 30s high 20s and would stay at 40 instead of 44 psi. We checked the logs and it lost voltage at the same time it leaned out. It went from mid 14s to mid 10's and at the same time fuel pressure went down. I have been having to jump start the car everytime I return the car to stock or when loading a new tune because the fuel pumps stay running with the key forward so I just picked up a new battery today and will do an alternator as well. Should I go with a 130amp or a 200? I haven't had time to really dig into the car since it happened last night and I'm working today but I figured I'd see if there is anything else I should look into for when I get home.

 

[Sonicblue_s197]

Forgot to mention it's a 3 valve with the JPC racing triple pump return style fuel system

 

[JeremyH]

Sounds like alternator could be on its way out, when mine went it was intermittent and voltage would randomly drop when it wasn't working. As for the fuel system itself I would check all the wiring/relays fuses etc.

 

[Sonicblue_s197]

Do u think the 130 is good or should I just go for a 200 amp?

 

[JeremyH]

If you getting a new one I would get nothing other than a 2010 oem version personally.

 

[Sonicblue_s197]

What's the difference from a 2010 and an 05?

 

[JeremyH]

If you do a search you can find info on it as well as the part number and best place to get it. Here is a post from one of the threads I quickly searched for.

Put a digital voltmeter across the battery. Should be aprx 12.5 vdc with eng off.
With eng on, it should read 14.4 vdc. If it still reads 12.5 or less... the alternator is toast. You can also read the battery voltage off the OBD port. It's one of many parameters that can be displayed on the aeroforce gauges.

IF the battery was toast, it just won't hold a charge... but it won't suck the 135A alternator down to the point where the vdc is < 12.5 vdc.

If the alternator is toast, replace it with the 135A alternator from the 2010 mustang GT. The 2010 alternator drops right in....and is a 3 phase type. The 05-09 cars got the single phase version. Single phase alternator's went the way of the do-do bird years ago.

 

[Sonicblue_s197]

Thanks for the help man, I tested both new and old batteries and the new one tested 12.4 and the old one that was in the car tested 12.5 off the car. IL do some more digging and go with a 2010 then

 

[JeremyH]

Mine was a tricky bastard, I was getting random car not starting issues but everything would measure fine car on and car off. That went on for months until finally the car started bogging and then dying while driving. I jumped it and put the voltmeter on it watched voltage go up and down finally and knew it was shot.

 

[Sonicblue_s197]

Is that alternator straight bolt on? Wires and all?

 

[Pentalab]

Is that alternator straight bolt on? Wires and all?

The 2010 alternator is a direct swap into any 05-09 car, wiring and all.

 

[Sonicblue_s197]

The 2010 alternator is a direct swap into any 05-09 car, wiring and all.

Thanks man, IL swing by ford this morning hopefully they have in the area