MSII to HEI RPM value 1/3 actual

[Jnewcomb]

Hey Guys, I am slowly getting things to work on a SB Chevy fuel only set-up and using TS to test before installing TBI unit. The RPM consistently shows a value approx. 1/3 actual RPM (285 RPM). This messes up everything as it thinks it is cranking off and on. I have fooled around with cylinder count thinking it would half/double based on this setting, still no change. This is a large top early HEI, connected to the "TACH" terminal on the side next to the "+". I have wired the MSII for optical input by TachSel- Optoin, OptoOut-Tsel, and XG2-XG1.
I have been attempting to view input from distributor on portable oscilloscope, but seems to be a square wave with a leading high spike. Does this seem normal? My next attempt will be to inject signal on relay board "Tach" terminal and try and find how it triggers with different frequencies.
Any pointers would be greatly apreciated,
Thanks,
jnewcomb

MSII V3.0 board
FW V2.891
TunerStudio MS 0.999.7
Inovative WB LC-1

[Matt Cramer]

Please post a copy of your MSQ file - this will let me check all your settings at once.

[Jnewcomb]

Matt, thanks for responding. I am including my .msq for your review. Hopefully you can spot a dumb mistake in my settings.

[Matt Cramer]

No obvious mistakes in the configuration. What do you have in the D1 and D2 slots?

[Jnewcomb]

Matt, both D1 & D2 have jumpers installed. Of course I did not go with the shorted D2, so if it is needed I will need to remove the jumper and solder in D2. Should I give this a try? This is a stock 4 pin with shielded cable back to relay board with shield to TPS return.
Thanks,

[Matt Cramer]

Yeah, you may need the diode as you're triggering off the negative terminal of the coil. That might help.

[Jnewcomb]

Matt, I am heating up the iron tonight and installing one of the diodes. I guess I did not understand, I thought the 4 pin HEI was a nice clean 12 volt square wave and not the same as triggering of coil from points. I will post back later with results.
Thanks again,
Joel

[Matt Cramer]

The 7 pin HEI is a square wave signal. The 4 pin HEI is the same as points.

[Jnewcomb]

Matt, the diode did not make any difference to the RPM displayed in TunerStudio. If you are saying the 4 pin HEI is same as points, should I try the instructions for reverse biased zener in D2 position? Do I want to go down the path in instructions for 50B "triggering off coil negative"? Will I have to reverse this when going to the small cap HEI 8 pin MS ignition control later? I do not remember these details in your Nova project car with fuel only.
Thanks,
Joel

[Matt Cramer]

Matt, the diode did not make any difference to the RPM displayed in TunerStudio. If you are saying the 4 pin HEI is same as points, should I try the instructions for reverse biased zener in D2 position? Do I want to go down the path in instructions for 50B "triggering off coil negative"?

Yes.

Will I have to reverse this when going to the small cap HEI 8 pin MS ignition control later? I do not remember these details in your Nova project car with fuel only.
Thanks,
Joel

Different coils have different amounts of noise. The V3.57 has a setup that "splits the difference" - it has two diodes in the circuit but not a reversed zener.

[Jnewcomb]

Matt, over the weekend I tried the Ed capacitor and the backwards 22V Zener diode. The RPM is still hovering around 300 and can not be correct. I am beginning to think I have a bad combination of module and coil. Viewed on a scope the signal has steps before the high voltage spike, not a good looking square wave.
I did not want to go this route until I had the injection working, but I have ordered a pigtail for a 8 pin HEI distributor from DIY-Autotune. I will take out the zener and place 1N4001 in it's place. Then add a pull-up resistor to tach input, so as to look like the 3.57 board. At this point I will be ready for MS timing control only on a HEI8 small cap distributor.
Unless you can think of another modification, this is the route I will take to avoid this battle. The 8 pin should be easier from a trigger pulse stand point and would have to be done eventually for complete system. I was just trying to follow your lead with the Nova project and start with the fuel only.
Thanks for your help so far.

[Jnewcomb]

Matt, I installed the small cap HEI8 distributor and modified my circuit for inverted input using 1K pull-up resistor. Started it right up without the "B" wire on Vref. However, still had 1/3 RPM reading that it should have. Pulled it back out and fixed it until it broke. Evidently I shorted something or static got to the Daughter card, as I had nothing for RPM any longer. Bit the bullet and purchased another daughter card. Installed and flashed to 2.891 again, started up and RPM now looking proper. When I tried computer timing it would not run for more than a couple of seconds. I watched your HEI Nova video and noticed my dwell and skip tachometer pulses were different than yours. Modified to correct values and I now have a computer controlled ignition system.
So it looks like I had a bad MSII daughter card from the begining, it looked good through all the tests on the simulator, but for some reason it was dividing pulses improperly.
Thank you for your support so far and I hope Santa brings you that twin turbo for the Nova Project.
Joel