ECU Pin 109 Source

[My1GLaser]

I have a 350 rpm discrepancy between what my tach says and the rpm log on my dsmlink. Does anyone know what the source for ECU pin 109 is on a 1g? (I assume thats the input that dsmlink logs) It says it is for igniton pulse tach input, but I need to check the source and see if I can test it and/or run another source from an accurate sensor. There are obviously multiple sources since there were 2 choices for running my MAFT rpm wire, and I guess there is one from the coils also...

 

[dsm-onster]

Pin 109 = "Ignition pulse detect-Fuel Pump Control"

See 1990-1994 DSM Information for good 1G ecu info. . .

Be careful. I believe there are two sourses too. But I think one is "cleaner" than the other. You may get "glitches". . . where the ecu cannot read the tach if you use a fuzzy or unclean source.

 

[luv2rallye]

On a 90, ECU pin 109 gets it's signal from the "OR" signal output from the coils. You must have the "tach noise filter" installed which outputs a filtered signal for the tach (note the tach noise filter's input is the "OR" signal however).
See: http://www.dsmtuners.com/forums/showthread.php?t=147266

 

[steve]

Good posts guys.

The signal on pin 109 isn't used for the ECU's RPM input. It's used by the ECU to verify that that the power transistor worked and that the coils have power. The ECU has a much better source for RPM information from the CAS. So the ECU RPM is correct since it uses the CAS signals to time everything and fire the injectors and ignition where the factory tach is off the other end connected to pin 109.

Steve

 

[My1GLaser]

What is the "OR" signal output? What does this noise filter look like? My dash tach works, but there is a discrepency with what the ECU sees.(according to my DSMlink) I would be more than happy to replace this noise filter if I knew what it looked like. Both of my harnesses were out of the engine bay so I could clean, prep & paint, then they were rerouted. So, I do not know if the noise filter made it back to its original location. I did not own the car when the harnesses were in the original position, and the motor was already out when I got it. As far as the coil... on the coil front there is a small black thing bolted to it (about the size of a tootsie roll--noise filter?) and on the back of the coil there is a flat black square (I assume its the ign. module though I can't really read what is says.)
Here is a question (I know I am full of them...first DSM) When I replaced my fuel system from the filter to the AFPR I wanted to prime the system to check for leaks. I hooked up the bat + to the fuel pump test connector on the firewall to power it up... well I found out that I really hooked up to the tach connector for a handheld tach tool. Could that have caused problems in this circuit? I don't know where that "tach connector" goes and I am assuming it is an output signal and wasn't too happy about my 12v input. (I guess it wouldn't have caused a problem if there isn't a ground in that tach connector circuit, right? )

Thanks for your help.

 

[My1GLaser]

Steve,
As far as the ECU being right, if DSMlink is logging what the ECU sees from the CAS then I think it is wrong. My car was bogging down badly at idle, 475 rpm (bad o2 sens & TPS needs adj) according to the tach and my Link was logging 800+ rpm. It definitely felt like it was idling well below 800 at that time. I have an RPM signal to my MAFT tapped into one of the CAS wires. Could that be causing a disruption? Boy am I a mess

Edit: I just logged a run shifting at 3000 rpm in 1st-3rd and DSMLink has me at about 4000 rpms. I don't think there is any way I was at 4000 rpms. If so, I should have hit full boost 7-800 rpm earlier and I was still at about 7psi. (I'm running 12psi for now) I have leak tested and fixed them all.

Any ideas as to the discrepency? I swear my tach is right!