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RPM feed into Plex Knock Monitor V2

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Hi guys

For those that have a Plex Knock Monitor version 2, can you share some ideas on going about getting engine speed into the unit, particularly on a car that's still running the OEM ECU.

I currently have an innovate inductive clamp wired in to mine but it's not very practical to fit in place and then run the car out on the road with the hood down.

For one the clamp itself is huge and incredibly cumbersome and then the couple times I've got it to fit when I ran the harness out with the hood down it started melting from the heat.

Really looking forward to hear some ideas because not being able to get rpm into the unit is really a deal breaker.


Also interested in this. Hopefully I can contribute when I receive my v3 in a couple of weeks.

Andre mentioned in a webinar that there was an update to v2 that allows CAN integration. Could that work for your application?

Doug I'm really looking for a quick and easy implementation that can work on any car regardless if it's new or old.

Hi Christopher, it's been a long time since I've added rpm to my plex but the easiest/quickest solution for a temporary install is to take rpm from an injector signal. This is covered in detail under 'Step 3' in the instruction manual so I won't go into more detail. It wouldn't be difficult to make yourself up some jumper connectors for common injector plugs like EV14 etc.

Hi Andre, thanks for the insight.

Just one question, if you don't use the rpm input then are you using the device with solely audio? If so, then how are you able to log where you encountered detonation on say a ramp run? Are you listening and looking at the rpm in real time? If you can elaborate on the way you use the device I'd appreciate it.


You use the device when steady-state tuning. So you know the RPM, and the current load, you can adjust the ignition timing directly. If you encounter knock during a ramp run, you immediately stop and adjust the ignition timing (you'll be within a few hundred RPM typically).

I'm not referring to using while steady state tuning...that part is self explanatory.

I am referring to optimizing the ignition advance wot ramp runs on a reflash application. How do you use the tool in that scenario without the rpm input ?

I would stop as soon as I detected knock. Go back to the cells just before you stopped, and take out a few degrees of timing. Reflash and repeat.

Now with an OEM ECU, you may not even detect the knock, the ECU might trigger and retard the ignition -- you can use those clues in your log, to reduce the timing so that knock retard never occurs.

Knock is more common with higher engine temps, so want to make some WOT pulls with a very hot engine to make sure there isn't any knock.

Thanks for that David, my biggest issue with the plex and audio is knowing what to listen for. I am not experienced enough to identify knock via the audio. This is why I'm using the rpm vs load threshold within the plex software to visually see spikes. I run my Plex on 2nd harmonic mode and use the 10k filter but still it's really difficult to pick the knock from the background noise

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