Where are the N2O electronics experts? Need help.

[TT5.9mag]

Gentleman, I installed an NOS 2 stage window switch (only using one stage) on the D100 over the weekend and got it all wired up. The instructions with regards to rpm signal were vague and the unit I am using is primarily designed for efi stuff so typically you tap in to a single coil on a COP setup. The instructions say “coil trigger” wire. Now, I am using it on a carbureted application with a TPS (already had it for my trans) and a single MSD coil and mopar electronic distributor fired by a 4 pin HEI module. I have the rpm signal wired to the neg side of my coil with my tach and the “c” terminal of the hei. The RPM on the unit at idle is correct and tracks exactly with my tach. As I rev the engine slowly the displayed rpm goes erratic and jumps all over the place (while the tach continues to be accurate) rendering the unit basically useless as the function of a window switch is to trigger the nitrous at a preset RPM. I’ve read about maybe needing a resistor inline (what value?) or maybe needing an MSD tach adapter to clean up the coil signal. Anyone have any words of wisdom? Thanks in advance.

This is the window switch
https://www.holley.com/products/nitrous/controllers_and_accessories/controllers/parts/15982NOS
These are the instructions
https://documents.holley.com/d0323b6734a254e5eb0279950d473fc3af8651e0.pdf

 

[MadScientistMat]

I'd first try grounding the unit directly to the battery. Also, where's it getting 12v power? These tend to be very common noise sources.

If that doesn't work, I would only then try filtering the input signal. You can try a 1k, 1/2 watt resistor inline first, they're pretty cheap
If that doesn't work, this module might. I designed that one when I worked there, but I no longer have any affiliation with them other than knowing what's inside the box.

 

[TT5.9mag]

I'd first try grounding the unit directly to the battery. Also, where's it getting 12v power? These tend to be very common noise sources.

If that doesn't work, I would only then try filtering the input signal. You can try a 1k, 1/2 watt resistor inline first, they're pretty cheap
If that doesn't work, this module might. I designed that one when I worked there, but I no longer have any affiliation with them other than knowing what's inside the box.

Thank you. I was hoping you’d chime in and I’m glad you did. I am powering the unit from an unused key on fuse location on the original fuse block of the truck. The ground is currently to bare metal on the firewall shared by 3 other grounds. I will move that directly to battery neg and see if there is any change. Also, Holley tech said 500-600 ohm resistor in line “should” work. I’m more inclined to listen to you. I’ll try the 1kohm 1/2 watt first. And if that doesn’t work I’ll try the isolator module you built.

 

[TT5.9mag]

Ordered these.
McMaster-Carr
I’ll have them later today and I’ll give your suggestions a try tonight and report back.

 

[MadScientistMat]

The 1k value was more of a starting point without full info on what's in the box. If you lose the signal, try a lower valve.

But I'd move the ground first. The power point sounds OK - typical trouble spots are things like the coil positive wire.

 

[TT5.9mag]

Have to apologize, worked late last night and didn’t mess with the truck. Hopefully today I’ll get a little time.

 

[TT5.9mag]

Ran home on lunch because it was bothering me. Hooked up a 4ga ground straight to battery negative. That did nothing. Hooked up a 500 ohm resistor in line, that did nothing. Cut that out and hooked up a 1k ohm resistor in line and that did nothing. The issue is the exact same regardless. Video is uploading now. I’ll post it soon.

 

[TT5.9mag]

 

[MadScientistMat]

This is just a garden variety HEI, no multi spark feature or anything?

If there isn't anything exotic about this ignition, I would try checking it with some other source - maybe another car, maybe an Arduino or frequency generator. If it passes there, I'd try the AXM-110.

 

[TT5.9mag]

This is just a garden variety HEI, no multi spark feature or anything?

If there isn't anything exotic about this ignition, I would try checking it with some other source - maybe another car, maybe an Arduino or frequency generator. If it passes there, I'd try the AXM-110.

Yes sir, just an over the counter 4 pin hei module from Napa triggered by a stock mopar electronic distributor.

 

[Bobzilla]

The instructions you posted says it can be connected to coil trigger wire and then unit can be adjusted to the correct number of times per engine revolution that the wire is triggered. So it should work on your setup.

So, maybe it's getting EMI from another nearby wire. I like the idea of trying to run a tach wire from another vehicle parked next to this one, or using a signal generator if you have access to one. Maybe even just wrapping a shield wire along the length of your trigger wire and grounding one end of it.

 

[TT5.9mag]

The instructions you posted says it can be connected to coil trigger wire and then unit can be adjusted to the correct number of times per engine revolution that the wire is triggered.

I did try all of the available settings in the unit to see if there were any changes. None of them matched rpm at any engine speed. Only the “V8 single coil” setting matched rpm and that’s where I have it set. I do believe it is directly related to the tach signal generated by the hei module. I’ve read that the hei tach pulse has its own special intricacies that have to be filtered around for electronics. Analog devices seem to not have a problem.

 

[RustyRatRod]

What they'd say down in my neck of the woods... "Mah, you thankin to mech. Just put the nitrogen on it and hode on, yo"

 

[TT5.9mag]

What they'd say down in my neck of the woods... "Mah, you thankin to mech. Just put the nitrogen on it and hode on, yo"

That’s funny a bit ago a friend asked me what I’m going to do for this weekend (we’re supposed to be making passes on Saturday). I said set all this **** to zero and turn the nitrous on at full throttle and send it. So…….thats the plan. I ordered some different value resistors and a couple capacitors. I’m going build a filter from plans I found on some GM hei sites. If that don’t work its going back on a button.

 

[Bewy]

Below is another HEI amp that I have used & it works. I would also keep the trigger wires going to the G & W terminals twisted & away from the coil [-ve] wire. I use Co-axial microphone cable for the trigger wires, with co-ax braiding earthed.

 

[TT5.9mag]

Below is another HEI amp that I have used & it works. I would also keep the trigger wires going to the G & W terminals twisted & away from the coil [-ve] wire. I use Co-axial microphone cable for the trigger wires, with co-ax braiding earthed.

View attachment 1716490001

Thank you! What did you use that for? A tach or some other device? I do have that pair of wires twisted and separated from anything else.