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Discussion Starter · #1 ·
Hi,
I have 95 impala ss stock 95K miles, installing ZEX wet nitrous system. I have a fuel pressure switch (33 psi) at the fuel solenoid; from there it goes to the fuel rail at the Schrader valve. When the system is activated it pulses on and off, if I bypass the fuel pressure switch – no pulsating. What could be the problem and how to fix it?
Also I have MSD window switch(8969), which drops out like it loses the tach signal. I get the tach signal from the – side of the coil.
Thanks
 
G

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Discussion Starter · #2 ·
If it pulses with the fuel pressure safety switch (FPSS) and doesn't without it, it is definitely a fuel pressure issue. Either your fuel system is not capable of pushing that volume of fuel at 33 PSI or the FPSS is set at too high a cutoff point.

Are you still using the stock fuel pump? If so, sn upgeade to at least a Walbro 340 pump would be wise, and adding a Racetronix FP harness will give you even more flow capacity.
 
G

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Discussion Starter · #3 ·
It has stock fuel pump and regulator.
Could it be the regulator? How do I check if is the fuel pump or fuel regulator?
Thanks
 
G

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Discussion Starter · #4 ·
get a fuel pressure testing gauge. Hook it up to the shcrader(sp) valve and test the pressure. Regulator usually tests good if you remove the vacuum line and fuel pressure jumps up. Pressure should be at least 40psi with vacuum line on regulator.
 
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Discussion Starter · #5 ·
I hooked up a fuel pressure gauge, the results are:

1) With the engine off, ign on: about 36psi

2) With the engine running idle about same 36psi

3) With the engine running blip the throttle, jumps up to about 40psi then back down to 36psi at idle

4) With engine running at idle pull off vacuum line from regulator: about 40psi


Any thoughts
Thanks
 
G

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Discussion Starter · #6 ·
Your test conditions do not simulate a full throttle drag strip pass at all. An engine under load uses MUCH more fuel than one sitting in the garage in "park". It is not your FPR that is the problem, it is your ability to deliver enough gallons/minute of fuel at WOT. The only way to measure the fuel pressure in this condition is to do it on a dyno or during a full-throttle drive. And your N2O system will have to be functional too. You apparently don't have a fuel pressure issue on just the motor, so it will only show up when the N2O system requires additional fuel. When you can't deliver enough VOLUME of fuel, the pressure drops.

Save yourself a lot of trouble. Install a Walbro 340 fuel pump and your issues will disapper. So many of us have already had your problem and solved it with a Walbro pump. You have the opportunity to learn from our experience here.
 
G

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Discussion Starter · #7 ·
1) With the engine off, ign on: about 36psi

2) With the engine running idle about same 36psi
Motoralldata specs;
Fuel System Pressure [1] 41.0 to 47.0 psi

[1]. With engine "OFF", ignition "ON", and the fuel pump running. Fuel system pressure with engine running at idle speed will be lower.
Your fuel pressure is not up to spec let alone going to keep up with a decent sized hit. You gotta pay to play. *if you want to keep it in one piece*

cheap intank pumps $105 ... DO iT!

full voltage to the pump you need it..... so.... DO iT!

You will be missing parts of the pistons. Or the rods will go S-shaped if you dont get FUEL in check. AKA new Motor


Your wet nozzle and jet JUST ADDS fuel to offset the extra power the kit makes. The injectors are providing the majority of the fuel if you are low in pressure they are starving.

5 & 7 WILL have less pressure than you are going to see on a gauge at WOT since the test port is on the inlet side & 5 and 7 are at the end of the fuel plenum. Each injector is going to enduce pressure and vol drop all the way to the regulator IF the pump cant keep up. The pressure and AFR can look good and 5 & 7 can be in danger!

One could also make argument that the inake manifold was NOT designed to flow fuel. So how do you know your nitrous enrichment fuel from the jet is making it evenly to all the holes. You don't and it won't. Thats ANOTHER reason why you have to run extra rich to make up for error in the system like this.

Our group needs another Fast B-Body at the track!
Spend some money to get some fuel to the rail.

TAD

[ 05-14-2007, 12:30 PM: Message edited by: ProTools4 ]
 
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