Inductive tach pickup on coil-on-plug?

My favorite and most-often used motorcycle doesn't have a tachometer from the factory, which is a shame, but it has many other upsides, so for years I have shifted by ear, played it safe with the revs, and moved on. It is a 2016 Husqvarna 701 Enduro.

I finally splurged for the TrailTech Voyager Pro GPS plus instruments, and by most accounts it is awesome. I generally love all the functionality, but the tach doesn't work reliably.

TrailTech says oh...you don't have a separate coil? Well, just wrap the wire several times around the tip of the coil at the spark plug end (jam/wedge it under the rubber boot) and then play around with the number of wraps and the pulse setting until it seems to work.

I've done that, and landed on a setting that has it sort-of working, with a notable delay when at its best, but then as soon as it gets hot it flips out and starts rhythmically spiking, even when rpm is steady, and shortly thereafter starts reading 20,000rpm plus.

The erroneous readings start when it is hot out, and/or riding at low-speed, and/or heading uphill, and/or using larger throttle openings. Very frustrating, and makes it such that the tach function is borderline useless.

Anyone had success with getting an inductive 'wrap-it-around-the-coil-lead' aftermarket tachometer working with an integrated coil on plug? If so, what did you do?

Anyone have any ideas for a rock-solid aftermarket tachometer that integrates easily with COP setups?

This bike is a single-cylinder four-stroke and has a dual plug setup for complete combustion, but both plugs fire every combustion cycle, only the exact timing is fine-tuned. Both plugs have the coil integrated on the plug.

Im just about to tear into it again, so any input is appreciated!

Is there no tach output from the ECM to the gauge cluster? My 690 had a factory tach that I removed, I wonder if there's a pin that's just unused in the ECM connector since the bikes with the newer engines don't have a tach. On my 990 I was able to pick up that signal, and I also ended up using a fairly large resistor in line with that with my Voyager Pro. It still jumps around at times, but usually it is okay and there's no lag. It does seem like the noise suppression circuitry in the Voyager Pro isn't very good. Make sure the ground on the gauge is very good as well, ground noise was also part of my issue.

My 690 is a fairly dedicated rally race bike, so all the stock gauges have been removed. I wouldn't worry too much about playing it safe with the revs - every time I go from racing the FX450 (11700 rev limit) to the 690 (something like 8500 rev limit) the first half hour of a stage I'm constantly in the rev limiter because it takes a minute to recalibrate my ears. The rev limit on these bigger thumpers is super low, they pull right up to the limiter, and 8000 rpm is right where the power is on the FX. It has held up just fine to the abuse. I'm not saying you should go pound the limiter all the time, but it's very unlikely that you'd hurt it if you went out and accelerated through a gear until you tapped the limiter just to see where it is every once in a while.

I agree with gearheadE30 - I'd think an RPM signal should be coming off the ECU somewhere and would be much more reliable than an inductive pickup wrapped around the coil and shoved down into the head. 

Did any versions of this bike come with a factory tach? if so, I'd look into how the factory tach got its signal. 

a lot of times an inductive pickup around the coil trigger wire from the ecu still works. Good call though if a version of this bike has a tach the output wire from the ecu is still probably there just unused/unpinned.

Thanks for the input. It would be awesome if there was a tach output from the ECU, but I don't know how to go about figuring it out. I'm not aware of any Husqvarna 701 Enduros or Supermotos that came with a factory tach. My Husky is 2016. The repair manual I have has wiring diagrams that are system-specific. Here's an example:

One grey box is the ECU, and the other is the combination meter, with specific pins called out for this subsystem. Then there are sensors, IAT, CLT, Lambda, and the sidestand switch. Of course there are other pages of similar diagrams, but it isn't like some manuals I've had with a complete vehicle schematic and/or complete pinouts for connectors. If a component doesn't exist on my bike, I don't think I can find any information on which pin from the repair manual, unfortunately.

Some older KTM 690s came with tachs, but they also had quite a few differences to my bike, such as carbs, or EFI but no drive-by-wire throttle, single plug, plus a totally different dashboard, so I doubt that they are similar enough to crossover. Some newer street bikes come with tachometers, such as the 690 Duke or Husky Svartpilen/Vitpilen 701, but those have the newer version of the engine/ECU, with lots of stuff I don't have like dual balance shafts, traction-control, lean-angle-sensitive ABS, totally different TFT display, etc. 2019 and newer 690/701 Enduro has some spendy European aftermarket options for tachometers, but it is a different ECU, so I can't imagine it is compatible.

What I need to know to move forward is was there a 690 Enduro with EFI, drive-by-wire throttle, dual spark plugs/coils, ABS, and a factory tach? The ballpark year range would be 2014-2018 I think? If so, it seems like to be the case, but the next step is to confirm if the ECU is the same as the Husky?

My Google-fu has lead me to threads of people wondering and musing about the same things I am wondering about, but no real conclusions.

Did some more digging and some more searching this evening, and found evidence of KTM 690s from the same date range as my bike with a tach...a very traditional analog tach...in orange.  Furthermore, my searching found many complaints about failures on the stock instrument cluster!

I also found that some aftermarket units like the Cumpan use the crank position sensor output for the tach. Hmm...

If the crank sensor is hall style with a regular tooth pattern that can work decently.

If you can get a digital tach output signal, you can use a spike signal converter made from a relay to generate something that looks like a coil kickback spike. That's how I drove the stock tach from the Megasquirt digital signal on my AE92. In your case I suppose you'd need to ground the spike signal and then put your inductive pickup on that wire...

In reply to ae86andkp61 (Forum Supporter) :

My 690 is a 2014, and is the first year of ABS, electronic throttle, dual plugs, etc. I believe it's fundamentally similar to the 701, but the 701 I think got a slightly different version of the engine and they became the same in 2019. But the ECU may be the same. 

I have all the wiring diagrams for the 2014 bike at home, I'll take a look and see if there's a specific callout for the tach in there. Unfortunately I seem to remember it being a random bundle of wires shown between the ECU and the cluster with no functional callout, but it might be possible to check which wires are common and which are not since I think everything except the tach signal would be the same.

GameboyRMH said:

If you can get a digital tach output signal, you can use a spike signal converter made from a relay to generate something that looks like a coil kickback spike. That's how I drove the stock tach from the Megasquirt digital signal on my AE92. In your case I suppose you'd need to ground the spike signal and then put your inductive pickup on that wire...

That only works if the tach out transistor has a high enough output limit, otherwise it clips it before it can trigger the tach. It will be very circuit dependent. 

In reply to gearheadE30 :

Awesome; thanks for the confirmation that such a beast exists on the KTM side! The part number for the ECU showing on AOMC's online parts fiche is the same for the KTM and Husky, FWIW.

Any information you can share from your wiring diagrams is much appreciated!

In reply to ae86andkp61 (Forum Supporter) :

After looking at the diagram for a bit, most of the signals to the cluster are pretty easy to account for because things like indicators are triggered by discrete components like the neutral switch or the oil pressure switch. The only wires that go to my stock tach-equipped cluster that don't come from a specific switch/sensor or CAN are:

• white: ECM pin 28 to gauge pin 11
• White/Green: ECM pin 14 to gauge pin 4
• Black/Green: ECM pin 43 to gauge pin 12

The 690 does some unexpected stuff with CAN and relays some stuff through the ABS module, but my tach still worked without the ABS module connected so I don't think it's a CAN signal.

My notes aren't as good as they should be, but either white or white/green was the FI light, because I know I kept that wire. I'm leaning towards white/green but it's been a while since I built that wiring harness.

I was hoping there would be some color standardization, but my 990 used blue/white for the tacho output, and that's not even a color combo that shows up on the 690 diagram.