I'll give it a shot in the AM. Thanks again!!
Regarding the previous code changes - Do I keep them or revert back?
Hi,
A suggested circuit from another thread.
http://forum.arduino.cc/index.php?topic=26678.0
And another.
The second pulse or glitch, is due to oscillation when the equivalent of spark OFF occurs.
The first circuit looks as if it filters the glitch.
Tom... 
Regarding the previous code changes - Do I keep them or revert back?
I've used your original code to add the 2000µs debounce, there's nothing left to do but test.
Looks like TomGeorge has a possible hardware solution.
You scope trace was really helpful!
Yes indeed, very helpful. Everyone has been very helpful as a matter of fact. Everyone's help is greatly appreciated. This project has been going on for quite some time now. This is the last hurdle to get over.
It works!! Thanks for all the help!! I'm attaching a working copy of the code. I had to fix the RPM calculation. Thanks again!!
FreqTach3.ino (14.2 KB)
I just can't find this H11L1M chip anywhere in this country! Could I use some other opto instead??
No, Living currently in Vietnam so post service here is highly unreliable, never know if you will get it or not I did find other link where they did use 4N35 opto.. but it was little different and the guy went with some other design.
Well, let me know if you have any luck. I may be able to send a couple.
Any chance you could post a final drawing of the solution? I'm looking to do the same for couple of projects I have in the works and would like to build a small board to interface with the negative post on my coil.
I was able to connect the digital input directly to the 5 volt square wave signal coming directly from the ECU, which helped a lot. I'll look for any schematics that I might have and post, if that helps. I also received a tip from another follower suggesting to put a 47nf capacitor on the output side of the opto-coupler Schmitt trigger. If you want a good DIY tachometer project to make, I suggest one from Chippernut. It's what my current tachometer design is based off of. TECH - Chippernut Electronic Kits