OK, here's the deal I finally got my nitrous works kit hooked up last fall. I set it up with a 50 shot just to make sure all was good. Everything seemed to be fine. So I get my car out of storage last weekend and change the jets to the 125 shot I wanted to run. Seems to be fine until I hit about 4500RPM, then it kind of surges. I am thinking that the fuel pump isn't keeping up. Feels like the system is turning on and off. I think I set the fuel pressure switch at 38PSI. How low should I set that? Any ideas?

 

You shouldnt set it any lower. I assume your nitrous is set to run with approx 42-44 #'s of fuel pressure. I wouldnt go any lower than 38 on the fpss. Most kits are set a little rich for safety, but I wouldnt gamble on going below 38psi.

You may need to change your fuel pump or get a booster pump. If you havent already though, you may want to vertify that the fpss is actually at 38, before going any farther.

 

How's bottle pressure? Is the bottle full?

If they're fine..

Get a fuel pressure gauge so you can see what's going on under the hood... If the pressure doesn't drop much when you hit it, then the FPSS could be bad.. Those hobbs switches are garbage and go out all the time.

What jets are you running?

 

Any ideas on testing the setting on the switch? The bottle is not full, it has 2-3 passes with the smaller jets and a little testing of the purge valve, but the pressure reads 900psi. I am running jet sizes 52/33 wich Nitrous Works claims is a 125 shot but all other brands say those jets are for a 100 shot. thanks

 

That does sound like a rich 100 shot.

I use 57/33 for my NX 125-shot and it runs great.

Your bottle pressure sounds high enough that you're not empty yet. Maybe getting there, though.

What is your plug type and gap? If it's too wide, spark could be getting blown out at higher RPMs.

 

i had the same problem. It was my fuel pressure switch, it was mounted too close to the fuel solenoid. WHen the noid opened, the pressure would drop, and cut the system, then pressure would build, it would come back, etc etc repeating. I turned the FPSS all the way down to 25psi, it was better, but not 100% clean, still had a sputter when the fuel noid first opened. I bypassed the fuel pressure safety switch, problem solved..........

my advice to you, short out the terminals on the FPSS, and see how it runs. If it runs like a champ, u know your problem.

 

thanks Hawk, I'll give that a try. My switch is right next to the solenoid.

 

If your fpss is cutting on and off at 38psi and your fp is set at 42psi or above, then you've got a fuel delivery problem.

Turning down your fpss only allows your nitrous system to run with less fuel pressure, which causes a leaner condition.

IMO, if you drop the setting on the fpss, you're not fixing the problem, you're just bypassing the safety device (fpps). At 125HP shot, you may never have a problem running a bit lean, but then again...
ouch

 

what is the right way to set the FPSS? I don't know how accurite I have it set.