fuel Pressure

[Ralphcobra]

Guys: Over the winter I rebuilt my engine and a bunch of other stuff. I am still in the process of trying to get all of the problems straightened out with my road race car. I can not get the car to build more than 25 lbs. of fuel pressure. I have installed three different 255 pumps and a new kirban regulator.
I have not been able to find a kink in the fuel lines so I don't think that is the problem. New fuel filter. Checked the voltage to the pump , changed out the relay. New autometer fuel guage. Before the rebuild, I didn't have a fuel pressure guage so I didn't really know what the fuel pressure was, but the car did have a skip in it. I have tried restricting the return fuel line with car running and that does not seem to raise the pressure at all.
I am at my wits end with this thing. Anyone have any suggestions. Have already missed two race sessions because of this problem, and I really want to go to the open track event at Nashville in May, but if something doesn';t change I am going to miss it as well. Am open to any suggestions. Thanks, Ralph

[SVO-SMITTY]

Have you tried checking the nylon hosesand connectors that connect to the fuel rail?

[SVO-SMITTY]

Oh yeah, I think a bad injector(s) will cause a low pressure reading as well, but not sure.

[Ralphcobra]

FUEL PRESSURE

wELL i HAVE FINALLY FOUND THE CULPRIT. iF YOU BUY A NEW wALBRO THAT WILL PUMP MORE THAN YOUR STOCK PUMP, YOU NEED TO REGROUND THE PUMP ITSELF ON THE FRAME NEAR THE PUMP. tHE PUMP WILL NOT BUILD PRESSURE WITHOUT DOING SO. aSK ME HOW i KNOW, i HAVE BEEN FOOLING WITH THIS THING FOR THREE MONTHS TO FIND THE PROBLEM. rALPH

[SVOeric]

hey Ralph, what year svo was that, because the wiring runs differently on 84-85, and 85.5 -86.

[Ralphcobra]

fuel pressure

My car is a 86. I don't know if this would apply to the earlier models, but it definetly applies to the 86. Ralph

[SVO-SMITTY]

I wish I would have viewed this post earlier. I just had a Walbro 255 installed, and when I checked my fuel pressure, it was at 20. This wire that needs to be regrouded, is it in the fuel tank, or is it outside the tank, and what exactly did you do to cure the problem?

[Ralphcobra]

Fuel pressure

You have two wires coming out the pump on the poutside of the tank. Just unplug the black wire from thgr harness and entend it to some place on your frame near the pump with as short a wire as possible. I can almost guarantee you that your problem will be fixed. I am somewhat disapointed in walbro for not giving us these specific instructions. and believe me I tried everythinh before I found this fix. I also was not able to get much help from any of the forums. Ralph

[SVOeric]

SVOSmitty,

I think what Ralph is saing is that the ground that runs through the harnes wasn't good enough to run the pump.

The pump runs off one hot wire, and one ground,,, from what I read, looks like he just cut the ground wire, on the pump side of the harnes, and grounded it to the frame.

so his hot wire still runs through the harnes, but his ground runs from the frame rail, into the pump.

[SVOPaul]

Ralph, I believe you have found a bad grounding problem in your car and it is possible that it is in other cars as well due to age and/or climate. I have installed Walbro pumps on well over 20 Mustangs(a number of SVOs) and NEVER experienced this problem....so I don't think it is something Walbro failed to tell you.....but it is good advice for anyone having a similar problem.

Sometimes you have to be a pioneer when solving a problem, you probably did not get much response because this is not a common problem....

[indiana dave]

It's the resistor wire

See my other post on this subject... The stock ground wire is a resistor wire. It will only allow 11 (?) volts to the pump. This wire is what you're bypassing by grounding the pump directly to the body or frame.

[SVOPaul]

This is not the same as your car Dave, you have an earlier car that had the dual pump setup.....Ralphs car is an '86 and does not require that modification.

[SVO-SMITTY]

Well guys I found out what my problem was. It was the alternator and the fuel pressure guage. First of all the new fuel pressure guage was broke when purchase. Secondly, while driving, I turned on my lights and radio, and noticed that my air/fuel guage went way lean. When turned them off, the guage went back and forth between lean and rich. At any rate I went and had my alternator check and one of my diodes in the alternator was bad. So, I got a new hi amp one and that woke up the new fuel pump, and the new Walbro 255 woke up the new t3/t4.

[GT350R]

Hey Paul, have you seen any improvment by removing the resistance wire on the early cars with a stock pump?

I have a few mods going in and I dont think i will be able to get a pump in for a little while. I am planning on keeping the boost low for now, but I will take all the easy fuel improvements that I can get!

[SVOPaul]

GT350R, honestly I have never tried to just remove the resistance wire so I can't tell you what the results would be....might work and give you more fuel or it might burn the car to the ground..... wish I could tell you for sure but I just don't know....