strange 255 problem

[Reaper1]

The car is an '88 Shelby Z. Completely stock(for now, getting ready for future mods). The issue is WAY to high base fuel pressure.

Let me first describe the pump, as it seemed a little odd to the two friends who were helping me(both have 255's on their cars as well, installed by them).
First off the pump was physically large enough to make it EXTREMELY difficult to get the pump#1 in to the rubber isolator, and #2 in to the reciever cup once it was in the isolator. Secondly it has a rectangular electrical connection on it. Lastly, it has a wire mesh screen inside the intake port on the bottom. Both of my friends mentioned that their pumps were MUCH easier to install and looked slightly different from this one.

For the installation, I replaced ALL of the rubber line on the car. The in tank line is the propper SAE 30R10 and I removed the pulse damper in the tank. The fuel filter is also new.

I had brought over my Accufab regulator to use on this car to adjust the fuel pressure, but I quickly learned that it didn't work(I'll get to that in another thread)http://www.turbo-mopar.com/forums/showthread.php?t=14495. I replaced it with the stock regulator. Base pressure is about 70psi. Putting vacuum to it at idle makes NO effect. If you rev the engine a bit with vacuum hooked up it does fluctuate.

We verified the return line was not obstructed. If we crimped the return line, the thing will PEG a 100psi gage! I thought these pumps had about a 90psi saftey valve built in to them?

The question is, why can't I regulate my fuel pressure? Both of my friends have a 255 in their cars with stock sized lines and have no issues. What gives with mine?

[glhs727]

what's the part number on the pump? where did it come from?

[Reaper1]

LOL, kinda funny you ask this. I don't know the number on the pump...it's in the tank on the car. As for where it came from...I *think* it was FWD, but I bought it so long ago I really can't remember. It sat in a box for a few years before I even tried to use it, and that was almost 3 years ago! I got it the same time I bought some +40's, that's the reason I'm pretty sure it came from FWD. TU didn't carry injectors at the time.

[Reaper1]

I solved the issue. A friend and I found that the 1/4" return line was being VERY restrictive. We first just used a catch can off of the regulator. The fuel pressure was right where it needed to be. We then disconnected the line at the tank and used air to blow through the entire length, it was so restirctive that you had to hold the air nozzle on the return line! We took one off of a donor car and it wasn't nearly as bad. To determine where it was being restricted we cut it in the middle of the car and it was MUCH worse towards the front. It was blowing some really nastly looking stuff out, so at that point we decided to replace the line. At first we were just going to use the donor 1/4" line, but after a little bit of thinking I decided to just go ahead with the 5/16" and be done with it. The donor car is an '86 Turbo Z, so it didn't match exactly, but it does fit. We had to section the front part of it to get it in the car, but that was no big deal. The rear went in fine. After all of that the fuel pressure is right where it needs to be!

I'll post pictures later.

Thanks to all that helped!

[turbovanman²]

Glad you found it, its always the little things that add up, :thumb:

[MiniMopar]

I had the same problem in my Turbo Z. Pretty common, actually. I plan to upgrade to a 3/8 supply line at some point, so the 5/16 will do service as a return at that point. Not running out of fuel yet, so we'll see.

[WickedShelby88]

Wow. Those are the types of things you wish people talked about more often. I plan on replacing all the fuel and brake lines on the SC with stainless so I better up grade my fuel line size as well.