mrmint69

I just installed a supercharger and inline fuel pump. It is only reaching 2 to 3 PSI. It is a 6psi unit. It pulls great but at wide open throttle when it reachs 5000 to 6000 rpm it stumbles and the fuel pressure gauge drops to 0 for a 1/2 second and them back to full. It only happens when you really get on it. Please help. :

Spinner

A 6 psi pump is for a carbed car. Take it off and put a FI pump on there before you blow up your motor. These engines use high pressure low volume pumps.

respectirocz

is the supercharger a 6 psi unit or the fuel pump a 6 psi unit
it sounds like your problem may be insufficient fuel flow, WOT at 5000 rpm is probably the peak in fuel consumption and you may not be flowing enough fuel to the rail as the vehicles need

what is the flow rating on the fuel pump you installed

mrmint69

I received a fuel pump with the unit. It says 100psi on the side. I hooked up a gauge to measure boost and it only goes up to just above 2. I had no problem before the supercharger or pump installed. The fuel pressure will be 40 to 43 psi and in a split second drop to 0 and then regain back to 40+ as fast as it dropped.

Kevin Blown 95 TA

Sounds like you don't have fuel pressure when you need it. Is there a FMU involved? You could always pull the blower belt and run with & without the in-line pump and see how it behaves. Maybe your in-tank pump is shot, but enough to still run the car when it is NA. You could see if the FP jumps slightly when you turn on the in-line pump to ensure it's working. Without the in-line working, the car will do just what you're describing.

As for boost, maybe you aren't revving high enough to make the 6psi due to it falling on it's face when it needs fuel.

I'm also assuming your ignition is healthy - good plugs at a smaller gap, new wires, and an ignition amplifier.

mrmint69

I have all brand new: MSD 6btm, msd 8.5mm wires .35 gap, msd pro billet dist, zex plugs for superchargers, fmu, icm, fuel filter, msd blaster coil. The boost under hard throttle goes to 1 1/2 to 2 1/2 PSI and stays until the fuel pressure loss. I can make it to almost 6000 rpm right before it shifts so i know i should be at full boost by now. Where is the best place to get the most acurate reading for the boost gauge? I have been using the vacuum port on the drivers side middle of the manifold. Also my vacuum on the manifold reads 16 at idle and goes to 19 at 1500 rpm and higher. 105,000 miles with no mods except in last 500 miles. My 0-60 time is a disappointing 6.6 secs so i need to find some answers.

Injuneer

Have you got the FMU hooked up correctly? It's supposed to close down the return line to boost fuel pressure, proportional to intake manifold boost.

Exactly which "vacuum port on the drivers side middle of the manifold" did you connect to? The one for the EGR, or the one for the Opti, or the one for the power brake booster. Hopefully you didn't connect it to the PVC connection.

It would also help if you added basic info about the car, like the year..... for example, the vacuum connections on the drivers side of the intake are not the same for all years.

OBE1 95Z28

Verify that your in-line pump is running, if it's not your stock pump won't be able to supply fuel under the higher pressures that the FMU creates. Your fuel pressure should rise as you start building boost as the FMU senses boost pressure and starts restricting fuel in the return line, thus boosting fuel pressure. From what you stated, it doesn't sound like your in-line pump or your FMU is working properly.

mrmint69

My car is a 94 z. Is there a way to check the FMU? Also if someone can tell from the year what vacuum port to use for the FMU? The inline pump is very loud so i know the power is to it but don't know if it is working correctly. My mechanic think the stock pump might work but only to a certain point of volume. Any way to check the amount of fuel it delivers and not just the pressure. Thanks

OBE1 95Z28

A FMU can be checked by applying a know air pressure to the vacuum line (i.e. apply 6 psi) and observing that your fuel pressure rises.

Any of the small vacuum ports on the intake manifold can be "T'd" into to provide a vacuum reference for the FMU.

As Fred stated, just don't confuse the PCV connection for a vacuum source. Here's a photo of a 1995 intake from Shoebox's site, yours should be similar: http://shbox.com/1/opti_vacuum_conn.jpg