Installed Fuel PSI saftey switch, question

[95gtSTANG]

Hey guys just hooked up my NOS15685 fuel psi safety switch tonight. Overall it was very simple to integrate with my ZEX wet kit (#82023). I spliced the switch into the ground wire for the ZEX unit.

I used a test light hooked up to the fuse block to calibrate the pressure at which the circuit closes (or arms the system). I set the switch such that circuit is closed (nitrous on) with fuel pressure without vac line attached(39-40psi).

While doing this I noticed that when the circuit was not grounded and I had the test light on the ground wire (calibrating fuel psi) the car actually throttled up. Once I adjusted the diaphragm and the light turned On (close circuit) the rpm came down back to normal.

Any ideas why this would happen? I am not sure why adding a 12V test light to a wire that should be grounded caused a throttle response. It was like someone was stepping on the gas lightly. To be clear, the wire that I put the test light on was the NMU ground.

So here is a summary of my questions:
1) Why did I observe a throttle response when I put a 12 V test light on the ungrounded NMU ground wire?
2) I set the fuel cut off switch to kill the NMU ground when fuel psi is below ~39-40 psi. Is this too high? Any memory concerns with the NMU? Since it will almost always be off even when armed?

Thanks!
thanks!

[95gtSTANG]

I was on hold for quite a while yesterday with no answer so I figured I would get a response from the forum.....???

[amick]

The problem you are experiancing is due to the fact that you are breaking ground......breaking the ground causes feedback voltage through the white TPS wire. This is why the engine throttled up, the vehicle's ECU is seeing "floating" voltages fed back to it. Our ground wire must always be connected directly to ground at all times. You can setup your fuel saftey switch on either the power wire or on the white TPS wire but not ground.

Sorry you did not get an immediate reply but that is not the way the forum works. We answer the questions on here as we have time. It typically takes a couple days to get a response on here. As far as calling the tech line if you can just hold on someone will get to you. The calls are answered in the order they are recieved. We get about 1200+ calls a day so our Techs stay extremely busy. Sorry about the hold time on the phones. We do have e-mail and now instant messenger as well as these forums to ask questions.

[95gtSTANG]

The problem you are experiancing is due to the fact that you are breaking ground......breaking the ground causes feedback voltage through the white TPS wire. This is why the engine throttled up, the vehicle's ECU is seeing "floating" voltages fed back to it. Our ground wire must always be connected directly to ground at all times. You can setup your fuel saftey switch on either the power wire or on the white TPS wire but not ground.

Sorry you did not get an immediate reply but that is not the way the forum works. We answer the questions on here as we have time. It typically takes a couple days to get a response on here. As far as calling the tech line if you can just hold on someone will get to you. The calls are answered in the order they are recieved. We get about 1200+ calls a day so our Techs stay extremely busy. Sorry about the hold time on the phones. We do have e-mail and now instant messenger as well as these forums to ask questions.

Thanks for the reply, I figured it was some sort of feed back through the TPS but wanted confirmation. With respect to the ground interupt safety switch- you are recommending using the interrupt circuit on the power/ or signal side..Is this just good practice or is there a particular reason the NMU should stay grounded? I appreciate the advice.

Your recommendation seems to contradict a post I read few threads below this one...any thoughts?

I can't post links yet..
URL-nitrous-management-unit-ground-interrupt-okay-2601.html[/url]

[amick]

Whenever the ground is interupted on the NMU it will allow for voltage fluctuation to come through the white TPS wire so the TPS Sensor will not get a proper reading. Some systems will work fine with ground interupt but our NMU was designed to remain grounded. I checked that thread and the tech B16A2 is incorrect in her statement about that window switch. I will post a correction in that thread. I will also correct that technician to insure that does not happen again. Thank you for pointing it out.

[95gtSTANG]

Whenever the ground is interupted on the NMU it will allow for voltage fluctuation to come through the white TPS wire so the TPS Sensor will not get a proper reading. Some systems will work fine with ground interupt but our NMU was designed to remain grounded. I checked that thread and the tech B16A2 is incorrect in her statement about that window switch. I will post a correction in that thread. I will also correct that technician to insure that does not happen again. Thank you for pointing it out.

I am not sure who B16A2- that name was not in the post I referenceced. But I am glad you cleared this up-hopefully this will be helpful for all of the ZEX units. I also recommend this be updated in the instructions.

[amick]

B16A2 was the screen name of the first person to respond in the post you refferanced. They were the one that said it was ok to use the ground interupt window switch in that post. The post is no longer there because I had it removed to prevent futher confusion.