I just in stalled my MAP Walbro 400 with a Fuel labs FPR and FIC rail. I have FIC 1250 injectors. I installed 6an fuel lines from pump to rail. I set my pressure with no vacuum on the regulator at 44lbs. Everything is fine. I then installed the MAP rewire kit. I now have 80lbs of pressure at the rail. I cant get it below 60lbs no matter what I do. I have searched and found a few ideas that I'm not real happy with. Anybody had this happen first hand?

 

You can't reduce the pressure because the return system isn't designed to shunt so much fuel from the rail. A simple fix is here:

https://www.evolutionm.net/forums/ev...ould-know.html

 

yup, a full voltage rewire of a walbro 400 will do that. stock return line and siphon hole in the pump return are too small. you can first try drilling out the siphon, but i doubt it will help. next option is to use the factory supply line as the return. not sure if that will fix it either. be careful about the 60 psi - it might cause the return line to leak fuel.

 

i'm interested to see if drilling the siphon works in his situation. the factory return line is so dinky.

 

Drilling out the return siphon did not work for me. I just got rid of the rewire kit and measured voltage to the pump. Surprisingly the voltage stayed at 13V up until 6500 rpm where it dropped to 11.5 V. I would still like to find a different solution for the high fuel pressure with the rewire and the higher flowing fuel pumps.

 

If drilling the siphon alone doesn't work, it's because as mrfred pointed out, the factory return line is simply too small. My return line is upgraded to a 6-AN, but I still had a pressure problem until I drilled the siphon as per the above link. With two 255HP pumps in parallel running full time at >14V, I have no pressure issues.

 

Ted B, is the return line -6 from the rail to the pump?

 

The return line sends fuel from the FPR back to the pump assembly.

 

^ correct...lol. So your setup is -6 from the FPR all the way to the pump correct?

 

Ah, sorry, it's late here.

That is affirmative.

 

If everything was fine even after installing the -6AN feedline, and the new FPR & rail, until you installed the high voltage rewire kit, then why don't you just remove that hotwire kit and go back to the smaller gauge factory wiring harness. Don't you think that retrofit alone would cure the problem.

Try it, and if not then do TedB's fix, i.e., enlarging the pump's siphon hole and lastly retrofit the larger diameter fuel supply line to your original factory spec one. You are just pumping way too much volume at idle.

I wonder if it is possible the I.D. of the FPR's outlet hole is too small to bypass the increased volume at the rail even at idle. That 60-80 PSI reading was at idle right? Or are you setup to read fuel pressure at WOT as well?

 

I just bought this kit too and plan on installing it but I wanted to do it right before I tune. SO do you think after drilling out the siphon and going to get a tune will can get fixed? Or will i just have to upgrade my return line all together to handle the pump?

 

Because a return line overrun problem isn't something that can be 'tuned out', the smart move is to upgrade the return line and pump simultaneously.

 

so you think NOT running the rewire kit will be the only way this will work without making fuel pressure go crazy?

 

Perhaps, but then again, the pump will never deliver its full capacity without the rewire kit. If you are intending to use this with a factory turbo and gasoline, a single 255lph would have been plenty large enough, and wouldn't have presented this issue. If we are speaking specifically of the -267 pump for E85 use, then a factory turbo setup may get away with reduced voltage (factory wiring) and stock return line.