Having some fuel pressure issues.

[92EuroDiamante]

Hey everyone. I took my car out for the spring and am having some fuel pressure issues. Equipment is as follows.

Walbro 2xxlph fuel pump (forgot the exact number, the one everyone uses)
Charging and grounding wiring upgraded.
Fresh alternator that I rewound for higher output
Fresh battery.
I have not hotwired the pump, in the D you have to drop the tank to get to the pump, it would be a mess if not necessary.

I used to enjoy 40 something psi at idle and and good fuel pressure across the board.
Now I am getting very low fuel pressure, sometimes nearly 0 at idle, and sometimes pretty high.
I can start the car, let it warm up at idle with the low fuel pressure, then as I turn the key back to turn the car off (to ON or ACC position) The fuel pressure climbs right back up. In the ACC position I hear the relay click and fuel pressure jumps up further.

Any ideas? not sure if I am missing something like not putting this pump on stock wiring or something.

[92EuroDiamante]

played around with it some more.
Basically any accessory kicks it down to nearly no fuel pressure at idle, Fans, Bottle heater, even locking the doors!
Im getting 14.6v at idle.

[GTOJOE]

So you have done the fuel pump hotwire? sounds like somehting in your acc wiring has a short or something and is drawing too much power which is robbing power from your fuel pump. Run a hotwire and see if that improves anything but I would be looking for what is causing the voltage issues. you need to check the voltage to the pump when you turn on any of the offending circuits.

[92EuroDiamante]

No fuel pump hotwire. I didnt need it initially.
I will check for voltage monday hopefully, and do the hotwire at that time. A big project on the diamante because unlike the 3s you've gotta drop the fuel tank and not just the compartment in the back.

Im wondering about the power robbing idea. It makes sense, its just that basically anything causes it to go to zero. Things like the fans and bottle heater which are direct wired with a switch do it, but so do things that are part of the cars stock wiring still, like lights, and door locks.

[x2percentmilk]

Hmm, id be worried about shorts and grounds. I cant really provide any specific things to check, but thats got to be it. If the ground for the pump is bad it could give reason for the electricity to flow elsewhere when available, ie: when you use the accessories. Other grounds could be bad limiting totaly current, shorts cause similar issues, etc etc.

[92EuroDiamante]

I spent a while last night trying to find an electrical problem and couldnt. I disabled the lighting, all of the accessories and the accessory harness I made for fans, bottle heater and audio and it still had the same issue. If I turn the car off and leave the key in I can hear the relay clicking and the fuel pressure jumps up a few points after that so I know that is working.
I just pulled the tank and pump and everything looks good. Connections are solid.
Im wondering if its a bad pump.

Im off to figure out a way to hotwire this thing. Probably gonna have to remove the whole trunk to find the stock wire grrrr.

[92EuroDiamante]

I just put everything back together, all wiring done correctly, as it was the first time. All fuel lines like new, no leaks.
If it was the fuel pump it wouldnt start right up and drive fine under normal rpms (under 3k) right?
I havent pushed it because I dont want to damage anything.

Guess im gonna try another fuel sender, anyone in the chicago area have one I can test?

[RL7]

It very well could be the pump. Non authentic Walbro's have some serious build quality issues and the market is so flooded with them that retailers are often unaware they are selling knockoffs. I would say fuel pump first if your accessories weren't affecting things- that points to a wiring issue. You may want to try replacing the in-tank power and ground wires or at least check the voltage getting through them. (at the in-tank fuel pump connector).

[x2xtreme360]

Check voltage at the power wire to the pump. Turn on all accessories and check it again. Also, check the ground cable for any type of voltage drop. Go from the ground pin right to the negative battery terminal. The reading should be very low, 300mA or less to be exact.

[92EuroDiamante]

Thank you for the advice
Gonna check the voltage soon. I wanted to yesterday but the wire is under my trunk mold so I didnt have time to remove it. I figured its best to check it there and not right off the relay.