Fuel pressure too high w/SFMU (95 GS w/turbo)

sike · 12-16-2003, 06:27 PM

I just installed a turbo kit on my car. I'm using the Vortech SFMU for fuel management. I did not remove the stock FPR. and I read on vortech's page that running the SFMU with the stock FPR can cause very rich idle conditions, which I have (90 PSI at idle and durring boost). The fuel pressure does not change with adjusting the FMU, and it does not adjust to boost, so I'm led to belive the stock FPR is messing it up. How can I remove the FPR without having a big whole at the end of my fuel rail? Can I just remove the FPR, take it apart, and reinstall what is left as a cap? I need some ideas. The car is eating gas quickly, and hesitates majorly under boost.

leet · 12-18-2003, 01:38 AM

Get an adjustable FPR. Aeromotive makes a nice one.

DSMJim · 12-18-2003, 07:00 AM

You have something hooked up wrong. Can you show a picture of how you have the fuel hooked up or give me a diagram. It sounds to me like you have the FMU hooked up wrong as it should only be adding pressure with Boost. All it really is, is a fuel pressure regulator that works on a 10:1 basis not 1:1 like a stock regulator. It's just to ramp up fuel pressure quicker under boost for a non turbo car because they are not increasing pulse width as well as pressure like a normal turbo car.

It should be hooked up so that the output of your stock FPR goes into the side fitting ont he FMU, and the bottom fitting goes back to the return to the tank (that used to be attached to the back of the stock fpr) Then attach vacuum to the FMU from either your FPR or somewhere else off the intake manifold.

Try and not splice the FMU off your BOV or from check valves or anything like that. As pure a vac source as possible. And make sure there are no check valves between your intake manifold and FMU or FPR. Incase your not sure what a check valve is, it's the little plastic guy that’s inline with a vac line. It's a one way valve that allows air to travel one way.

If you have a check valve inline with your fmu it will allow boost to go through adding pressure, but can not go back because it's a one way valve and it will hold the fmu closed creating all kinds of pressure at idle like your experiencing.

Not saying your an idiot or anything just trying to help with every possible scenario I can think of.

sike · 12-18-2003, 02:25 PM

Well I read about the FMU at the manufacturers site and it said that using the stock FPR can/will cause very rich idle conditions, which I'm guessing is the cause. The FPR on the non-turbos is located at the end of the fuel rail and has no hose connections at all I'm not really sure how it works. I'm going to try an adjustable FPR and it should work. Going to a local DSM shop today and having them check it out.

sike · 12-18-2003, 03:59 PM

Instead of driving 2 hours to the DSM shop, I called Vortech, they had no idea what the problem could be other than the lines being hooked up wrong or, something being wrong with the FMU. I don't understand, the thing is brand new. I checked out the gauge again while driving, and the pressure actually decreases when the car is running hard. This is absolutelly killing me, I can't figure it out for the life of me. I'm absolutely possible the lines are hooked up right. I'm fairly certain the gauge is working properly, the lines feel like there is ALOT of pressure in them. Ahhh!

sike · 12-18-2003, 05:36 PM

I belive I found the problem. The diaphram (rubber seperator) inside the fmu was torn, it divides the vacuum between the upper and lower sections. I ordered a new one I'm going to try to repair this one just to see if it works properly with it fixed.

DSMJim · 12-18-2003, 11:38 PM

The fuel pressure regulator is at hte end of the fuel rail on ALL cars. The FMU goes after that. It should be the very last thing on your fuel line before it goes back to the tank. The regulator and FMU regulat the pressure from the pump to the injectors so they are last, not first.

Just make sure its after your FPR which is after your injectors (as per stock setup) if it's hooked up any other way then thats your problem. Maybe a pic or a drawn diagram of how you ahve it hooked up will help.

Using an FMU with stock FPR is not a problem, I do it all the time on Honda's so I speak from experience.

sike · 12-19-2003, 02:34 PM

There is nothing after the regulator, it goes back down to the end where the Fuel enters, and the return line is just above it.

sike · 12-19-2003, 03:26 PM

Nice ride by the way Jim.