Fuel pressure - why would a walbro need this much?

I replaced my stock 2 pump system on the Shelby Charger with a Walbro 255. I was running about 40 psi or so with +20s (vacuum disconnected). I could not get the car to idle (kept stalling) in open loop until the O2 gauge warmed up with 40PSI on the Walbro pump. I cranked the pressure up to 55 PSI and it seems much better and will idle. Why would I need to run that much pressure on +20s on the Walbro pump when the stock dual pump could run on 40 PSI?

Good question. I have a couple for you. Did you buy a new internal tank sending unit, or did you try to mount your 255 Walbro with the old two pump pickup? The two pump sending unit uses a 3/8" inlet, while the Walbro is a 5/16" outlet coming out of the fuel pump. If so, how did you deal with that transition? Did you take any pictures of the pump install? If so, can you post? I've seen plenty of fuel pumps hemorrhage fuel inside the tank. When this happens it sucks up air with the fuel. If you have a 1/2+ tank of fuel, this doesn't really matter, as it is pulling fuel through the areas that aren't sealed well. Without submerging pump in a bucket you will never know this. This was especially prone when using the two pump pickup. Another way of checking this would be to put a +12 source on the +side of coil. Disconnect fuel line in engine bay and see how the fuel comes out? is it steady stream with no bubbles. If so you can continue to drain fuel in a gas can and see "if and when" the bubbles start occurring. Could be half a tank, quarter tank, or if everything is well sealed and working properly, it will be the same until the fuel tank is empty.
Todd

Hi Todd. I mounted it on the old hanger. This pic doesnt help much but

http://s1256.photobucket.com/user/de...93636.jpg.html

I was able to put the flared metal line from the hanger right over the outlet of the walbro - butted up against it. ran that submersible fuel line to connect the two. Dont recall the size but it fit snug with 2 efi hose clamps.

This is with a full tank so I know the pump is fully submersed.

#1. Is the car stock?
#2. Do you have a wideband o2 sensor?
#3. What voltage is the Walbro seeing?

#1. Is the car stock? No. Converted to T2. +20s, Accufab APFR, ported head, TU60 turbo, NPR intercooler, 86/87 GLHS Stage 2 LM
#2. Do you have a wideband o2 sensor? No but I just purchased an Innovate LM-2.
#3. What voltage is the Walbro seeing? No idea. Can I get that from the connector on the fuel tank or do you mean right at the pump itself (pull the pump out)?

Thanks!

#4. What boost level are you running?
#5. Did you use a submersible fuel hose with the Walbro? 30R10 rated?
#6. Fuel filter changed?


Yes, getting the voltage at the connector at near the fuel tank is fine.
Without a wideband o2 sensor, we are guessing a/f ratio is ok...

#4. What boost level are you running? 18 PSI with manual controller
#5. Did you use a submersible fuel hose with the Walbro? 30R10 rated? Yes / Yes
#6. Fuel filter changed? Yes

OK will get a voltage reading at the tank.