Fuel pressure problems

[ASenna]

OK so after sorting out my charging debacle, I found out that I still have low fuel pressure related to the fuel pump, but I've helped it somewhat.

 

Here's some info: Walbro 255 inline pump on a circuit from a Megasquirt relay up front through about 10ft of wire. Very simple setup. Power goes to relay, opens, allows current to flow to pump.

Aeromotive FPR.

 

With 12.5V across the battery at idle, I'm getting 11V at the pump. So I wired in a hotwire from the positive battery terminal straight to the pump and got around 12.1V at idle, which is obviously better, but really weird considering I've got a direct connection from the battery to the accessory so it should be the battery potential (12.5V).

 

So I decided to take grounding out of the equation by wiring another wire from the negative on the battery terminal to the negative side of the pump. Still got 12.1V. My fuel pressure evens out at 39psi, and then bounces around from 39 to 37 for about 2 seconds, then evens out again. It's really weird.

 

Should be 40psi rock solid. Any ideas?

[roger.svoboda]

bad relay (by the way they close to give power not open). Too small wire gage going to the pump causing a voltage drop in the wire. Poor battery cables. You are using the same vom for all your measurements right? If your vom test leads are long enough check for a voltage drop from battery positive to pump positive. Could be the feed from the battery to whereever it goes and then to the relay and then to the pump. any suspect looking connections should be eliminated. every interconnection within the circuit causes some voltage drop but 1.5 volts is quite a lot.

[jasper]

A GOOD charging system at idle, puts out 13.6-14.2 volts. I would take another look.