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Forum nameEngine Management Systems & Controllers
Topic subjectMs2-Extra 420a/Neon Decoder tach issue
Topic URLhttp://forums.2gnt.com/dcboard.php?az=show_topic&forum=54&topic_id=3490&mesg_id=3490
3490, Ms2-Extra 420a/Neon Decoder tach issue
Posted by DirtMegirt, Dec-31-69 06:00 PM
A little background first...

Purchased Ms2 v3.0 back in April or so, and spent a few months on and off constructing the board. Read all I could, which I guess wasn't enough :scratch, and went ahead with a basic install. By basic I mean that I am not running anything with the ms yet. I tapped into TPS, Crank Angle, stock o2(did I even need to?), installed both GM sensors, and wired into power and established ground. I am eventually going to go turbo, as I have already rebuilt for it, and wanted to get the ms installed before doing so. Now the issue...

Everything ms seems to be fine as far as the readings that I am getting while in MT, except the damn tach. My first mistake was when I built the ms, I had read the posts by Corbin, Wicked and Gil about the tach spikes that they experienced with the 3.0 board, so I wired my board with this in mind and followed Corbin's fix for the situation found here:

MSnS V3 Board Tach Spikes Fixed!

No go. I still saw jumps in the tach reading. So I continued searching and came across Wicked/Gil's fix:

Running MSnS v3 Board as FULL Standalone (No Spikes)!

Now with this setup, I was able to get a steady tach signal, however, it seemed too far under what my stock tach was reporting( stock tach was at 950 or so and ms was in the high 600's/low 700's and as I would rev the gap would grow until it was around 1k apart up in the 4000's), so I continued to adjust the pots, and when The tach reading on the ms was VERY close to the stock reading, the spikes were evident again. It would spike from @950 up to @1300. I tried even finer tuning the pots, however to no avail. After searching more indepth on the ms2 site, I stumbled across what I thought was going to be my answer:

MS2-Extra Neon/420A Manual

I followed this setup and now my tach is up in the high 3000's and low 4000's. Also, it is still spiking. I was hoping that some of the ms guru's would have some suggestions?




One quick question about the wiring schematic. In this picture, are D1 and D2 supposed to be open? That is how I have them now. I had them both jumped before. At this point, the only thing that I can think of doing is increasing the value of the c12 capacitor. Thanks for any responses in advance.
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