After the Supercharger install I wanted to verify the accuracy of my electric gage....Got the right guage to go into the schrader valve and @ first it was pretty steady but I needed to change the pick up to 1/2 inch and install new shut off valve. Well now I fred it iup and the fuel preasure is all over the board looks like the guage is vibrating badly and I can not get an accurate reading to save my life. I am guessing that I have an air leak somewhere in the new pick up or valve connections some where. I am sure it is not in the pick up beacause I ran it with no shutoff valve and the preassure was steady...then installed new valve and now this.

What causes the mechanical guage @ the rail to bounce around wildly say from 20psi to 50 psi when the electric guage on the dash stays stable......Any thoughts?

Mechanical is at the Schrader valve...
electric is at the FMU unit from Procharger...
Help!

Bryan

Check for an air or fuel leak. Also make sure you dont have any blockages in the line or pick up.. Did you remove the check ball from the tank fitting when you went to 1/2' ?? Also a remote possibility of a bad or mis adjusted regulator or bad / leaking injector.. Unless you have a bad gauge.. Hard to tell for sure without being there, but start with double checking the simple stuff first.. Also make sure that the mechanical gauge is on properly.. Jamie / Lakeside

did u change the electric fuel pump during this install?

EFI or Carb?

dumb ? but I had a new gage go bad drove me nuts needle was not tight to shaft it was a holley brand

I had the same problem and solved it. Several important questions:
EFI or Carb?
if EFI- is it cool fuel setup with remote regulator(in cool fuel)?
if cool fuel- is it stock setup,pump and lines?
any fuel rail modifications?

EFI
yes on the cool fuel.....but it goes from the tank ,to the seperator, to the fuel pump, Aeromotive 1000, to the regulator,to the rail.....return from the regulator goes to cool fuel cooler and back to seperator.

No mods to the fuel rail.

How did you fix it?


Bryan

Bryan, I had the same problem with pressure guages in place of the schrader valves. Turns out the pressure pulses in the fuel rails created from the injectors opening and closing caused the guages to fail. When I put a shop type guage with a rubber hose on the schrader valve, the hose dampened the pulses enough so the reading was steady. Try it before you tear into anything else.

As sonic said, those pressure spikes are real. You need to find a way to dampen them out. A good gauge that is intended for EFI should be internaly damped, or like he said use a long line to the guage or a reservoir in between the rail and the gauge.

Sounds like you don't have the stock cool fuel setup. The pressure flutuations are caused because in a batch type fuel injector set up, 4 injectors are opening and closing all at the same time. Increasing the volume of fuel available in the hoses/rail will help reduce this problem. Also, having the regulator as close to the rail as possible will help. There are many people, including myself, that feel that the regualtor should be after the rail, not before it. The stock cool fuel setup has problems in both of these areas and they are magnified with any engine modifications, resulting in even more needle bounce. Do a search for "needle bounce" on this forum. There are a lot of previous threads on this issue. You will never eliminate the bounce but you can reduce it. and as the previous post states, these fluctuations will cause your gauges to fail and leak fuel into the bilge. I learned that the hard way....TWICE! Now my gauges have rubber hose between the regulator and the gauge to help prevent that. and buy GOOD gauges. Cheap gauges will fail quickly in this application.