General Strain Gauge/Load Cell with Stock Ignition

[Black'95]

I'd like to use a load cell shift knob to cut ignition during shifts but I don't want to move to a standalone ECU. A company called Xineering has a gear controller that will open a circuit (typically the 12V on a CoP setup) to cut spark and then PWM it back in for a smoother gear change. It looks like I could break into the PTU wiring and interrupt the 12V (pin 6) or possibly interrupt ground (pin 3) to achieve this, since I have an ARC2 CDI.

Are there any issues with this? It seems like it would work just fine to me... Pic of my current wiring with CDI for reference.

I can't interrupt the 12V to the coils since the CDI intercepts this and turns it into about 500V, according to Scott at Dynatek. The Xineering box is rated for something like 30V.

I can't interrupt the individual signals from the ECU since the Xineering box only has one output.

Thanks!

 

[danl]

The ECU might throw a CEL if it does not see a load on pins 2 and 7. I don't have a 2G to test this though. I don't think my 1G cares.

It looks like if you drop out pin 3 or 6 that removes power to the PTU. The PTU sends the signal to the tachometer on pin 4. So you would lose the tach as the shift is being interrupted.

 

[Black'95]

The CDI wiring is how the plug n play harness connects, I just drew that in so there was accurate info to reference. I assumed the tach would drop out for the shift as well, but the ignition will only be cut for a couple hundred milliseconds, so I’m not concerned with that. I was more wondering if there would be other unforeseen consequences or some reason that this can’t work? I assume the PTU can handle the interruptions and it would just fire the plugs whenever there’s power.

I’ve heard that a strain gauge with stock ecu and such has been attempted but it’s never worked, but I can’t really find any details on what people have tried and what went wrong for them.

 

[DSMPT]

According to your profile, assuming that you have ECMLink and dogbox but don't want to go with a full standalone to use a strain gauge/load cell knob.

I could be wrong since I am not following very well what exactly you are planning here and I don't know about that specific strain gauge/load cell knob you are talking about. But generally a strain gauge/load cell knob output is 0.5-4.5V. Normally outputting approxi 2.5V without load and increase/decrease approxi 2V from the 2.5V depending on how much load on the knob by pulling/pushing. So to use a strain gauge/load cell knob, you would need some ECU or device that can accept this kind of flexible signal or converter that can convert it to a simple on/off signal.

But you say "the controller will open a circuit", does this mean that the shift knob you mentioned comes with a 12V output option or a ground switch option or so? If it does, why don't you use it as a simple shift cut switch to just trigger the NLTS feature and secondary ignition map in ECMLink and control through ECMLink. I think in this way no need to rewire the COP/CDI. Or maybe use a strain gauge/load cell knob with an interface like K-Tuned programmable interface to send the shift cut signal to ECMLink. Don't those work with your case?

Sorry if I am not following and again I could be wrong since I have never used a strain gauge/load cell knob with stock ECU/ECMLink, just sharing ideas.

 

[Black'95]

You're correct; ECMLink with a dogbox! I'm not going to rewire the CDI as that's working just fine; the diagram I posted was just so you can see how it's wired up. I can't use the secondary fuel maps since I'm running flex fuel.

I would be connecting the strain gauge shift knob to a gear controller, which is what will be doing the work of cutting the ignition.

I could wire the output of the gear controller to the clutch switch and do that, but that's a fuel cut, which to my understanding isn't near as fast as an ignition cut and may not work as well with such quick state changes. I currently use the CDI for launch limit since it's a spark cut and use ECMLink for antilag.

I could wire the gear controller to the launch limit input on the CDI and use that, which I have done before with an S1 Sequential load cell gear knob. I had issues with both knobs they sent me so I had to return them. I could do this again but I'd like to PWM the ignition back in to soften the engagement as opposed to slamming it back on all at once. Using the launch limit input on the CDI also limits the ignition cut to only work above the launch limit. Not the end of the world, but if I can interrupt the PTU wiring like I think I can, it will be better.

 

[DSMPT]

You're correct; ECMLink with a dogbox! I'm not going to rewire the CDI as that's working just fine; the diagram I posted was just so you can see how it's wired up. I can't use the secondary fuel maps since I'm running flex fuel.

I would be connecting the strain gauge shift knob to a gear controller, which is what will be doing the work of cutting the ignition.

I could wire the output of the gear controller to the clutch switch and do that, but that's a fuel cut, which to my understanding isn't near as fast as an ignition cut and may not work as well with such quick state changes. I currently use the CDI for launch limit since it's a spark cut and use ECMLink for antilag.

Now I see. So the load cell knob that you mentioned actually comes with an external controller that allow you to adjust all the necessary parameters? If so that sounds pretty complete, wouldn't require a standalone if it works. Yeah to use all the parameter you want, you would need something more than ECMLink.
Sorry probably I can't be of much help here, since I don't have experience with this specific setup. But I'm curious how this would work. Do you have the installation manual or guid for that load cell knob?

I could wire the gear controller to the launch limit input on the CDI and use that, which I have done before with an S1 Sequential load cell gear knob

Also I'm curious about this, since I have the S1 Sequential load cell knob, too. Did you directly wire the S1 knob digital output to the CDI box? Or to a relay to activate and then the relay to the CDI box? S1 knob has a digital output besides the analog 5V output that is supposed to be able to activate a relay, so I thought at least you might be able to use it as a shift cut switch for ECMLink or the CDI box.

I'd like to PWM the ignition back in to soften the engagement as opposed to slamming it back on all at once.

Yeah if you want the ignition ramped back, you would need the controller or a standalone ECU.

 

[Black'95]

Yes, it's a complete deal! They use/recommended the PPG strain gauge knob. Here is a link: https://www.xineering.com/gcu.html

I had that S1 gear knob wired directly to the launch limiter input on the ARC2 CDI, and configured the S1 knob to pull its output to ground. The CDI would see that as a clutch in event and would cut the ignition. Here's the instruction manual for that unit: http://www.roadraceengineering.com/instructions/arc2_instructions.htm

That's cool that you have that S1 knob! I had two and they both failed all but immediately. I didn't even get out of the garage with the first one . They both started reading full load at all times and I couldn't get them to reset or anything. This was a couple years ago, so I reached back out to S1 to see if they'd figured out the problem, but I never got a response.

 

[steve]

Why can't this be used instead of the clutch switch for NTLS in ECMLink?

 

[Black'95]

I was looking for a spark cut rather than a fuel cut, that’s all. I was under the impression that fuel cut by itself doesn’t work as well as spark cut for this. Also I’m not sure how that would respond to PWM’ing the power back in.

 

[DSMPT]

I had that S1 gear knob wired directly to the launch limiter input on the ARC2 CDI

I had two and they both failed all but immediately.

They both started reading full load at all times and I couldn't get them to reset or anything

Sounds like you fried the 2 knobs. I am not 100% sure but I think the knob's digital output should have been connected to the CDI launch limiter input through a relay.

That's cool that you have that S1 knob!

Yeah I have had it for 4~5 years and has been working great so far with AEM.

I’m not sure how that would respond to PWM’ing the power back in.

Maybe you shouldn't use it for the fuel cut. I don't know how exactly the gear control box works but I think that's for making the ignition ramped back to soften the shock.

 

[Black'95]

Sounds like you fried the 2 knobs. I am not 100% sure but I think the knob's digital output should have been connected to the CDI launch limiter input through a relay.

I was on the phone with S1 a couple times and told the guy what I was doing and how. He never mentioned any relays or resistors, so I never tried anything. He did say that my knobs were part of a new batch with a firmware upgrade, so they were going to look into that. That would suck if that's all it was! I'd have to double check with Dynatek but I don't think that input on the CDI passes much current. It just waits to be pulled to ground. Maybe that is a problem though. I'll email them and ask.

Maybe you shouldn't use it for the fuel cut. I don't know how exactly the gear control box works but I think that's for making the ignition ramped back to soften the shock.

The factory ECU only uses a fuel cut to control RPM, so that's why I've been using the CDI. It's noticeably faster/more accurate than the fuel cut for launch control.

 

[DSMPT]

He did say that my knobs were part of a new batch with a firmware upgrade, so they were going to look into that.

Oh I see, maybe that firmware had a bug or so.

It's noticeably faster/more accurate than the fuel cut for launch control.

Yes that's true. I am aware and agree about that. I use only ignition control for flat shifting.

I know you have a reason but may I ask why you don't go with a standalone ecu? ECMLink is really good and friendly but when you want to expand your setup, it would be limited since it's still the stock ecu box.
Hope this would work as it should on DSM. Since nowadays the dogbox is one major option for manual guys due to lack of parts. This would be a great option for someone who switch to a dogbox but want to stick with ECMLink.

 

[bastarddsm]

forget the strain gauge. use your left foot, hook the clutch switch to a timing retard. like -70*

 

[Black'95]

I know you have a reason but may I ask why you don't go with a standalone ecu? ECMLink is really good and friendly but when you want to expand your setup, it would be limited since it's still the stock ecu box.
Hope this would work as it should on DSM. Since nowadays the dogbox is one major option for manual guys due to lack of parts. This would be a great option for someone who switch to a dogbox but want to stick with ECMLink.

Simply because I don't want to go through the hassle of a standalone. I'd more than likely pull the entire harness out and make a new one if I went that route, and DSMLink is doing everything else I need it to, so it seems a bit much to go to all that just for a strain gauge setup... It would also be really nice to figure this out so I can make a thread about it and others can follow suit!

forget the strain gauge. use your left foot, hook the clutch switch to a timing retard. like -70*

I just thought it would be nice to get away from all the body movement to minimize the chance of missed shifts and such. Concentrate on other things, you know? Not that my car is THAT fast, but it should easily do 150+ in the quarter mile and I like to maximize the chances of my parts living a long life!

Do you happen to know if interrupting pin 3 of the PTU will work as an ignition cut?

 

[steve]

Do you happen to know if interrupting pin 3 of the PTU will work as an ignition cut?

It will certainly cut the ignition but I don't think the PTU is going to like it much. It might even cause engine failure if it accidentally coincides with a cylinder on the compression stroke firing early cause you just cut the charging current flow off.

I'll let you do the math to see how likely and at what RPM the coil dwells tend to overlap so that cutting the PTU off will cause an early ignition event.

 

[Black'95]

It will certainly cut the ignition but I don't think the PTU is going to like it much.

Will it damage the PTU? Does the PTU have to "boot up" or is there some kind of "startup" delay? I don't see why there would be anything of the sort, but I'm here to learn! I have random misfire detection turned off so we don't have to worry about that.

It might even cause engine failure if it accidentally coincides with a cylinder on the compression stroke firing early cause you just cut the charging current flow off.

That's exactly what I was afraid of, but I have two thoughts on that:

1: the normal operation of at least this particular ignition cut is to cut 12V to the coils, which I assume (just like you said) would fire that coil, no??? If I didn't have this CDI, apparently, I could do exactly that in my car, just interrupt the 12V to the coils and away we go, according to this company. Either way, a ton of vehicles are using this product without any issues so I'm not sure what we're missing.

I Just thought, even if the 12V gets cut, maybe the field won't collapse fast enough to fire the plug if the ECU isn't grounding that coil right then? I guess the voltage potential will just disappear rather than rushing to ground.

After thinking some more and a little Google, I think there needs to be current flowing through the primary coil in order to build the field that collapses to fire the secondary coil. So no ground, no current flow, nothing to fire the plug.

2: In my car, the CDI is looking for the ECU/PTU to pull an input to ground in order to fire a coil. If we're lifting that ground, it will never receive that signal to fire, right?

 

[steve]

I Just thought, even if the 12V gets cut, maybe the field won't collapse fast enough to fire the plug if the ECU isn't grounding that coil right then? I guess the voltage potential will just disappear rather than rushing to ground.

What happens in either case when you have a current in an inductor and you stop it, the voltage rises trying to keep the same current flowing. (Inductors resist the change in current). Doesn't matter too much if it's the high or low side that opens. The voltage across the inductor rises until the stored energy in the magnetic field is released. The release can happen in either the primary or secondary.

After thinking some more and a little Google, I think there needs to be current flowing through the primary coil in order to build the field that collapses to fire the secondary coil. So no ground, no current flow, nothing to fire the plug.

The CDI may (will) change the timing of when current is flowing through the PTU and also how much. Normal Kettering inductive ignition requires time to charge up the coil which is large vs the length of the discharge and was what I was thinking about when I posted.

The stock ECU uses fuel cut because it's easier on the engine and exhaust than spark cut which pumps unburnt fuel out the cylinders that ignites later. But some people like pop and bang tunes.

FYI, I'm not trying to keep you from trying this, only pointing out that there may be factors you haven't considered.

 

[Black'95]

The stock ECU uses fuel cut because it's easier on the engine and exhaust than spark cut which pumps unburnt fuel out the cylinders that ignites later. But some people like pop and bang tunes.

Emissions reasons and clogging the cat as well, I assume. This is definitely not being done for pops and bangs !

FYI, I'm not trying to keep you from trying this, only pointing out that there may be factors you haven't considered.

Yeah man, that's why I'm here, so thank you!

Are you thinking the PTU will be damaged by voltage spikes due to the ground being lifted?

 

[steve]

Are you thinking the PTU will be damaged by voltage spikes due to the ground being lifted?

Yes, that's my worry.

 

[Black'95]

Gotcha. I think I might have a spare, so if that’s the only apparent risk maybe I’ll see how this all works out. I can always fall back on using the launch control input on my CDI if I have to, so the strain gauge and GCU purchase won’t be a waste. Thanks for your insight!