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v3.1 weird rpm signal

posted Nov 26, 2017 05:07:28 by ChrisGonzales
So i purchased a prebuilt version recently tested it with the rpm simulator and all works. Tapped in the coil #1 on my car (2016 Mustang GT) and it reads weird. set it too 4ppr and at idle 650ish rpm it reads 8700 on the screen. But when i rev it to approx 1900-2000 rpm and hold it read in the high 200. Not sure if the signal is just a bad location. Doing all this under the hood testing pin locations. I have this connected directly to battery power and ground, i've tried different grounds with no big change. Does this need to be behind 12v switched power and is the a way to read the output from my car without an oscilloscope. I'm just a small tinker and don't have much in regards to tools like that.
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2 replies
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ChrisGonzales said Nov 27, 2017 07:32:07
So found out by a company that makes a single light shift light for my car, they were kind to share some info even though they didn't have to. Anyways. Apparently my car multi fires at low rpms not really sure i understand this if that means it occurs way faster or more ppr but he did mention around 3k it goes back to a single fire. And he mentioned the pulses are 1 pulse per 2 revs. So with that bit of info looks like i'm gonna need some custom code, which i'm a web programmer by nature so i can figure this out.

But what i'm unsure of is how to say hook up an arduino to test this info. I don't own an oscilloscope and would rather not have to purchase one just for this project i'm not truly familiar with all how that works, and if there is a way to accomplish this with an arduino and serial output please post below. Or maybe an inexpensive oscilloscope.
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jon.gulbrandson said Dec 06, 2017 01:04:13
Good info. That sounds like "wasted spark" - it's an emissions thing to burn off any excess fuel (if I recall correctly). Interesting that it turns off at some point, you'd have to create two PPr variables in the code and a cross-over point (probably RPM or throttle-position based). You could monitor this activity with an inexpensive DSO Nano or sound-card oscilliscope (with a laptop, for example). Otherwise it's going to be difficult to find the cross-over point and triggers.

Sounds like you'd probably be better served using the CAN system. There are arduino interfaces to pull the RPM, but if it's fast-enough to be a reliable shift light? I'm not quite sure. I know they've improved baud over the years but I haven't tested it.

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