03-30-2013, 10:51 AM
Join Date: Jun 2011
Location: Detroit Burbs
Total Cats: 3
LS coils - Tach Issue
I have done some searching, and some troubleshooting, but can't figure out how to make the stock tach work.
-'90 1.6L car (now has 1.8L VVT engine)
- Custom standalone ECU - uses 0-5V digital outputs for spark control. Stock ECU gone.
- GM LS coils - the badass ones with the heatsink on each coil. Standalone wiring between the ECU and these coils - no stock wiring interaction.
- I have the ECU driving both the stock 1.6L coilpack through the factory wiring and the GM LS coils in parallel. Ignitor and factory wiring harness has not been touched. Jumper harness used for ECU.
-Pin 2I on the ECU side is not connected to anything (BLK-WHT wire Pin E on the ignitor) - Ignition sense?
- I just physically unplug the set of coils I am not using - unplug the 1.6L coils at the 3 pin plug, and the GM coils at the stock GM 16? pin plug. Plug in the coils that I want to use.
- This provides me with the ability to use either ignition source, and no factory wires have been hacked. Yes - it was probably more work than required, but I really dislike hacking the harness if I don't have to.
-The engine runs just fine with either set of coils
-The tach works fine with the 1.6L coil plugged in.
-The tach does not work at all with the GM coils plugged in, and 1.6L coil disconnected.
Based on some reading on here, it looks like I might need a 12V pullup for the ECU pin 2I. But, I put a 1K resistor in the diagnostic connector between B+ and IGN- and no help there. Also, since the tach works fine with the 1.6L coil plugged in - this wire isn't needed??
So, I'm looking for some advice. I understand that I could use the tach out pin on my ECU and run that to the diagnostic connector in order to drive the tach. Maybe I will do that. But, I still don't understand why the tach doesn't work - when the only difference is the fact that the 1.6L coil isn't plugged in...
Why would the coil need to be plugged in if the ignitor is still wired up?