Chromeshadow

Technically this is very good, but this is exactly what I would not do. What you are doing is running the pulse to the injector to an antenna ( the wire you use to tap into it). It may work fine, or it may cause intermittent problems that would be nearly impossible to track down. This tapped wire will also change the shape of the pulse. The shape of the pulse (fast rising and falling edges) are crucial to the level of the spark.
Decreasing the slopes will decrease the voltage going to the plug. It may be fine, but it may be enough to cause a misfire at some point.

NELS GT

As a software engineer by day that sounds very appealing. So my one question comes from this part:

"Grab an engine pulse off one of the injectors, just tap a wire."

Truly just tap any wire from any injector? And I'll be able to find a discernible pulse pattern that matches the RPMs?

NELS GT

@Chromeshadow - our posts crossed. I'd love the ardunio route cause like I said I'm a coder but I'd like to make sure whatever I do on the electrical side / tapping any wires is all good.

Is there another place I could tap to get these pulses and feed it to an arduino chip?

Chromeshadow

RPM is available on the OBD II port, but reading it and converting to 0-5V it might be a big project. I don't know much about the ardunio unit, if it can read the OBD II info that would be really safe.
If I were going to tap of an injector, I would make a voltage divider to a ground near the injector and run shielded wire to the ardunio input. I'd start with a 10K ohm/50 ohm and take the signal from the middle. This should reduce the current pulse in the wire to the ardunio.
Still, if it were my car, I'd start from scratch and build something independent of the car electronics.

NELS GT

Yeah OBDII latency is bad though. On an automatic transmission it might be passable, but when you hit those gears and see the delay it would be bad.

Would this help me at all? Curious if it reads the pulses and spits out an analog voltage.
http://www.americanmuscle.com/autome...pter-9612.html

EDIT: from what I'm reading in the manual I think this could be a start for me... Now the question is how I can easily and effectively divide that 12V signal to a 5V maximum.
http://www.autometer.com/download_instruction/0561B.pdf

The reason I'm stuck on 5V is because I already have the lighting & dimming controller and that's what it takes - 5V full brightness, 0V no light.

Chromeshadow

Interesting! btw, our computers should have a tach output, you might be able to run it to the ardunio unit.

I'm not sure using the Autometer adapter will give you an analog signal, I think all tachs are actually frequency counters, they count the number of ignition pulses and convert them internally for the dial indicator.

Ford-a-tude

You are mixing two different concepts. I said injector, fuel injector. You start with injector and in the same sentence switch to spark. I wouldn't mess with the inputs to the spark plug coils. I suppose you could end up with a misfire by doing that, which is why I did not suggest that. I know it will work fine because when I installed my alarm and remote start I did exactly what I suggested. This is how the unit knows the remote start has successfully started the engine.

Chromeshadow

Ford-a-tude you are correct, I did jump from injectors to ignition coils. Glad to see you have tried this successfully.
Autometer also taps into the injectors, I'm sure they would get complaints if this was a problem.

jz78817

it's quite likely the cluster operates the tach off of CAN messages and not a direct signal.

NELS GT

Thanks a lot guys.

I'm going to grab an Arduino and try what Ford-a-Tude advised.