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Discussion Starter #1
Hi:
I'm trying to solve a problem in which my engine refuses to rev beyond 4250RPM and as part of the diagnostic process, I'm considering building up a homebrew datalogger for my 24 Hours of Lemons track car -- a 95 Tbird 3.8L w/ Splitport swap.

Initially, it will be to confirm that my ECU is not cutting out the spark and the injectors at the problem RPM. I will document this further in a separate thread (along with how I pieced together this datalogger).

For now though, I could use some data on the characteristics of the diagnostic signal generated by the Ignition Control Module and sent back to the Program Control Module (the PCM aka the ECU).

Q: What is the voltage and characteristics of this Ignition Diagnostic Monitor signal? Is it a straight 12V PWM signal? I figure it's PWM as that's the most logical signal BUT I have no clue as to if it's 12V or 5V.

Thanks in advance for your advice.
Regards,
-g

FYI:
For Debug, I'm planning to capture the following signals:
RPM (12V PWM), Spark Signal (12V PWM?), and Injector Duty Cycle (12V PWM).

Longer Term, I'm thinking of capturing: RPM, MAF Voltage, and O2 signals to aid in tuning...

Again, I don't want this to be a tuning thread. I'll open another one for that. If one of you knows what the IDM signal looks like though, you'd be a great help.
 

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Discussion Starter #3
I want to know what this signal is and I figured this was the most appropriate forum (as opposed to general tech, transmission, suspension, etc). Feel free to move it if you know of a better sub-forum.

By Tuning, I didn't want this thread to devolve into "oh, you should be logging this signal or that signal" or "hey, have you looked at xxx as why your engine won't rev beyond 4K". I will open up a separate thread once I have tracked down some additional info.

Thanks,
-g
 

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Discussion Starter #4
From this URL, it appears that the Ignition Diagnostic Monitor is indeed a 12V Signal PWM signal... at least for the the 4cyl ESCORT engine found in Spec Racer Fords. I can't imagine that it will be very different for other ford applications.. unless one of you folks know otherwise.

http://www.mummbrothers.com/SRF_Stuff/SRF_WiringChart.xls

It appears that i can grab the data I need to figure out my problem. The next step will be figuring out how to integrate this into my Lemons Car.
http://www.dataq.com/products/startkit/di149.htm

-g
 

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The ignition is ground side controlled from a 12 volt source. Just like the oldschool distributors had points that closed (dwell time ) to induce voltage in the coil, when the ground is turned off the spark occurs - except it is done by a transistor in the ICM instead.

Shouldnt you be busy watching the game ??? :tongue:
 

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The ignition is ground side controlled from a 12 volt source. Just like the oldschool distributors had points that closed (dwell time ) to induce voltage in the coil, when the ground is turned off the spark occurs - except it is done by a transistor in the ICM instead.

Shouldnt you be busy watching the game ??? :tongue:

So that's the ignition control (ECU -> Ignition Module); from the EVTM, it sounds like there's a second wire going from the Ignition Module BACK to the ECU.
Is this the same signal?

Yes, I'm here watching it with my friends. Since SF is getting it's butt handed to it, I've got time to spare.

I just hope that the Mission doesn't burn down. I'd rather not have my dollars pay for another bus :)

-g
 

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Ugh .. terrible game.

The IDM is the diagnostics monitor back to the PCM if there is a problem.

The Spout connector is what the PCM uses to provide the timing advance to the ICM, this is a good place to tap into to check the spark output the PCM provides.
 
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