I don't see how that could create an issue. Even if the return line were wide open, that shouldn't prevent the FPR from doing its job. You can almost be certain that you will need to take it apart, check your wiring, and have a good look at things.

 

I would wire the second pump from the battery direct with a hobs switch and relay, only on while boosting, sounds like you're over loading the existing wiring.

 

If the wiring (which he's upgraded) were insufficient, there would not be 13.5V at the pumps while in boost.

 

i have not checked volts under boost yet, just at idle but i will be check under load tonight. lets say they volt do go low under load what should i check/change to try and correct it?

 

If the voltage drops under load, you need to rethink your wiring. The best option is to route the existing wiring to a relay and draw pump power directly from the battery.

 

Sounds like one of the pumps isn't working to me. 40 psi at idle and 20 psi under boost? At 20 psi boost, you should see 60 psi fuel pressure. Sounds like once the fuel demand is up, the pumps(s) can't keep up. That big of a drop would seem like one isn't running to me.

How exactly is the second pump wired again? You know that the stock pump is on a dual circuit, right? A low voltage for idle conditions and a higher voltage for higher demand that is switch based on certain conditions. You're not tapping into the low voltage circuit, are you?

 

Pumps are ran off a distribution block straight off the battery. So they see a constant 13 volts at idle.. what should the voltage be under load?

 

Where are they grounded? Any chance you are grounded off a switched circuit that loses ground for one of the pumps?

Voltage under load ideally should be as close to idle as possible, but depending on wiring, etc, it may drop a bit. I really don't think that's the issue here. The fuel pressure is dramatically dropping under boost when it should be rising.

 

My pumps see around 14v under load, with a power feed right off the battery (triggered by a relay). My ground is a dedicated ground for both pumps. If you see anything less than 13.5v to the pumps while under load, you're losing pump capacity.

A drop to 20psi under load is dramatic. That type of problem shouldn't be too difficult to isolate.

 

well once i get done with work tonight i will head to my shop and take pictures of the setup and how things are wired. that way you guys arnt guessing and can help me a little more since im not a wiring genious.

 

well like i said i got some picture and no laughing at the wiring job.
in tank pump relay wiring,
#30- constant power from battery
#85- relay ground
#86- spliced white wire on top of pump wire on car side "blue connector"
#87- spliced white wire on top of pump wire on pump side "red connector"
#87a- not used

inline pump replay wiring,
#30-constant power from battery
#85-relay ground
#86-signal tap on passenger side flood single white wire
#87-positive power ran down to inline pump
#87a- not used

here is some of the picture any ?s just ask n ill try to explainor if you see the problem let me know.


the relay lay out im using.... both are from the stm pump rewire kit

distribution power block

relay grounds

signal wire taped into for lower pump

lower inline pump ground

the white wire splice for intank relay

everything

lower inline pump position

 

scotchlocks? ewww. did you at least strip the insulation off all the way around the wire before you put it on?

 

inline pump replay wiring,
#86-signal tap on passenger side flood single white wire

What exactly is this tapped into?

 

not sure i think it is the signal wire for the pump i just followed this ams install and recomened to use that wire.

http://www.amsperformance.com/instru...l%20System.pdf

 

Unless I am missing something obvious, the wiring seems fine. I'm not sure what your problem could be, unless one of the pumps is losing connection under load or something like that.