Testing/Bypassing FPSS
Thread Starter
11 Second Club
Joined: Nov 2001
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From: NE PA
Testing/Bypassing FPSS Ok, I've been thinking that I have a problem with the FPSS that came with my kit for awhile now because of some intermittent spraying issues I've been having. I was going to try bypassing the FPSS to eliminate or identify it as the problem, but Nitro Dave and others said that might not be such a great idea if it turned out that the FPSS was fine and that I had a fuel pump problem. 
Anyway, just to be on the safe side, I went ahead and installed a brand-new Lingenfelter/Walbro fuel pump in the car this weekend and I'm having the same problem. It fact, I don't think it's spraying at all now, so here's my question.
If I want to bypass the FPSS, can I just bypass it electrically, i.e., remove the two ground wires coming from it (one from the relay and the one from the window switch) and connect them together or do I also have to physically remove the FPSS from the fuel plumbing?
Thanks!
Anyway, just to be on the safe side, I went ahead and installed a brand-new Lingenfelter/Walbro fuel pump in the car this weekend and I'm having the same problem. It fact, I don't think it's spraying at all now, so here's my question.
If I want to bypass the FPSS, can I just bypass it electrically, i.e., remove the two ground wires coming from it (one from the relay and the one from the window switch) and connect them together or do I also have to physically remove the FPSS from the fuel plumbing?
Thanks!
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Joined: Jul 2002
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From: Dallas, TX
Trooper,
Tell me what you figure out on that FPSS. My buddy said many peopel have problems with them. Mine si on right now, still nto completed though, and am interested in your response.
Thanks
Gary
Tell me what you figure out on that FPSS. My buddy said many peopel have problems with them. Mine si on right now, still nto completed though, and am interested in your response.
Thanks
Gary
isnt so much being a bad fpss...just might not be adjusted properly...basically what someone allready stated, just connect the 2 wires comin off the switch and that completes the circuit, basically bypassin it. if it helps your situation id try and adjustin it first before automatically assuming its bad...goodluck..let us know how it turned out.
Thread Starter
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From: NE PA
Well, I did back it off about a 3/4 turn with no luck, so I just want to bypass it altogether first just to see if it's the source of the trouble or not. If it's not, I don't know what in hell it could be. I've checked everything else. 
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Thread Starter
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Joined: Nov 2001
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From: NE PA
Well, I bypassed it and now I'm spraying again, so it must be the damn FPSS.
Now I'm beginning to think that "some" of the problems I was having with my first rpm window switches were actually being caused by the FPSS!
Now I'm beginning to think that "some" of the problems I was having with my first rpm window switches were actually being caused by the FPSS!
TECH Enthusiast
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From: Dallas, TX
Maybe I should TAKE MINE OFF!!!!!!! It is on right now, but I might think of just leaving it off. What do you think?
Can it be adjusted?????????????? I don't see why it can't? But man these things cause more issues than they are worth
Gary
Can it be adjusted?????????????? I don't see why it can't? But man these things cause more issues than they are worth
Gary
Thread Starter
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From: NE PA
Originally Posted by 2001 Red Coupe Bandit
Maybe I should TAKE MINE OFF!!!!!!! It is on right now, but I might think of just leaving it off. What do you think?
Can it be adjusted?????????????? I don't see why it can't? But man these things cause more issues than they are worth
Gary
Can it be adjusted?????????????? I don't see why it can't? But man these things cause more issues than they are worth
Gary
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Joined: Jul 2002
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From: Dallas, TX
shitcan it LOL 
I told my guy that peopel have had issues, but he said he will adjust mine and it should be fine.
Trooper did you adjust yours with a fuel pressure gauge when you first put it on and set it? Or did you ever test it to determine what it was set at when you got it, or did you just put it on out of the box.
I told my guy that peopel have had issues, but he said he will adjust mine and it should be fine.
Trooper did you adjust yours with a fuel pressure gauge when you first put it on and set it? Or did you ever test it to determine what it was set at when you got it, or did you just put it on out of the box.
Last edited by 2001 Red Coupe Bandit; Sep 28, 2005 at 06:43 PM.
yeah..they are often way off....mine worked good for the first couple months i had it than just like that, it started acting up...i bypassed it and havent had any issues since. i have a NX one...dunno if you fellas have something differant or the same one but bypassin mine all together fixed all my problems.
Thread Starter
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From: NE PA
Originally Posted by 2001 Red Coupe Bandit
shitcan it LOL
I told my guy that peopel have had issues, but he said he will adjust mine and it should be fine.
Trooper did you adjust yours with a fuel pressure gauge when you first put it on and set it? Or did you ever test it to determine what it was set at when you got it, or did you just put it on out of the box.
I told my guy that peopel have had issues, but he said he will adjust mine and it should be fine.
Trooper did you adjust yours with a fuel pressure gauge when you first put it on and set it? Or did you ever test it to determine what it was set at when you got it, or did you just put it on out of the box.
Also, my experience was the same as TNTramair's. It worked fine when I first put in on and I did make my best run with it to date, but then it started giving me fits until it reached the point where it quit working altogether.
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From: Dallas, TX
Yes,
Mine is an NX FPSS. Maybe after you use them awhile the screw gets turned or moved and it isn't a device that you can set once and forget it.
It seems that you need to monitor it more often. I hope the saftey that teh FPSS switch provides is worth all the headaches
I am tempted to bypass it, but I guess I will give it a try. How do they test it. Where do you hook up a gauge to on the FPSS to test what PSI it is set to? Not really sure I understand how to adjust it if you can't physically look at a gauge of some sorts or mechanism that allows you to test what pressure the switch is at.
Couldn't you just set the pressure a little higher so it only goes off it there is a major failure and so it won't trip a false alarm so easily?
Mine is an NX FPSS. Maybe after you use them awhile the screw gets turned or moved and it isn't a device that you can set once and forget it.
It seems that you need to monitor it more often. I hope the saftey that teh FPSS switch provides is worth all the headaches
I am tempted to bypass it, but I guess I will give it a try. How do they test it. Where do you hook up a gauge to on the FPSS to test what PSI it is set to? Not really sure I understand how to adjust it if you can't physically look at a gauge of some sorts or mechanism that allows you to test what pressure the switch is at.
Couldn't you just set the pressure a little higher so it only goes off it there is a major failure and so it won't trip a false alarm so easily?
I connected mine to my air line. I had the regulator backed out to 0 psi. I hooked up a continuity tester to the FPSS (you could use a 12V test light if you want). I slowly turned the pressure up at the regulator and watched the guage. It was is set at about 38 psi out of the box. You could adjust it this way if you want to.
There is no rocket science to a FPSS. It is just a normally open switch, meaning when there is no fuel pressure the 2 terminals are not connected. When the pressure rises above the psi it is set at the two terminals are connected internally just as if you touched the 2 wires together.
Besides testing the psi setting above you can test it on the car this way. Take the wire off that goes to the relay. Make sure the wire you took off cannot touch ground. Get a 12v test light or a regular 12v bulb in a socket will do. Connect 1 wire from a 12v source to 1 wire fron the light bulb. Touch the other wire from the bulb to ground to make sure the light comes on. Then connect the wire you just grounded to the terminal of the FPSS you took the wire off of. Then turn the ingition on or start the car. As soon as there is fuel pressure the light should come on. Put the light bulb in the car or tape it to the windshield where you can see it. Take the car out and test it out. If the light says on the FPSS is not tripping the relay and shutting the system down. If the light goes out that is when the FPSS is shutting the system down.
There is no rocket science to a FPSS. It is just a normally open switch, meaning when there is no fuel pressure the 2 terminals are not connected. When the pressure rises above the psi it is set at the two terminals are connected internally just as if you touched the 2 wires together.
Besides testing the psi setting above you can test it on the car this way. Take the wire off that goes to the relay. Make sure the wire you took off cannot touch ground. Get a 12v test light or a regular 12v bulb in a socket will do. Connect 1 wire from a 12v source to 1 wire fron the light bulb. Touch the other wire from the bulb to ground to make sure the light comes on. Then connect the wire you just grounded to the terminal of the FPSS you took the wire off of. Then turn the ingition on or start the car. As soon as there is fuel pressure the light should come on. Put the light bulb in the car or tape it to the windshield where you can see it. Take the car out and test it out. If the light says on the FPSS is not tripping the relay and shutting the system down. If the light goes out that is when the FPSS is shutting the system down.
11 Second Club
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From: Boring Green, Kentucky
I have been studying this issue for many months. And the sponsors all defend the product, but it's history record speaks for itself. I kow they want to protect us from engine dismantling, but this thing needs more R&D.
I'm waiting on a friend to help me install my wet kit before finaggling with the NX FPSS.
XTrooper, I feel your frustration, and although you dished out some extra cash for the fuel pump, it is also pretty good insurance. If you can't run a FPSS, the next best thing is to assure your fuel delivery as much as possible.
I guess I'll post up when I get mine in...btw...all the guys in our local club run without it because of it's erratic nature.
I'm waiting on a friend to help me install my wet kit before finaggling with the NX FPSS.
XTrooper, I feel your frustration, and although you dished out some extra cash for the fuel pump, it is also pretty good insurance. If you can't run a FPSS, the next best thing is to assure your fuel delivery as much as possible.
I guess I'll post up when I get mine in...btw...all the guys in our local club run without it because of it's erratic nature.
Thread Starter
11 Second Club
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From: NE PA
Well, I'm looking into an A/F ratio nitrous shutoff switch now as a possible replacement for the FPSS. If I do get one of them, it will hopefully be more reliable than the fuel pressure switch.
I'd also like to see someone use my idea of incorporating a fuel pressure gauge into the FPSS so we could know exactly where it was set at and easily be able to adjust it. As I said earlier, I'd be happy to pay the difference in cost for this convenience.
2001 Red Coupe Bandit: It doesn't really matter who you got the FPSS from as all the nitrous vendors I'm aware of use the same source for them.
I'd also like to see someone use my idea of incorporating a fuel pressure gauge into the FPSS so we could know exactly where it was set at and easily be able to adjust it. As I said earlier, I'd be happy to pay the difference in cost for this convenience.
2001 Red Coupe Bandit: It doesn't really matter who you got the FPSS from as all the nitrous vendors I'm aware of use the same source for them.
Last edited by XTrooper; Sep 29, 2005 at 06:14 AM.
