CAM input circuit for MS2, 4G63
 

I recently built two MS-IIs on V3 boards for two different Miatas, both 90-93 1.6s. Both displayed the same problem, sync loss with sync loss reason = 38. Using the diagnostic in TunerStudio, both units in both cars showed noise in the cam signal. After many, many tests and board alterations, I was able to solve it by using a second optoisolator (4N25) on the cam input circuit as well. I completely removed the suggested circuit (IAC1A to JS10 with a 470 pullup to 5V) and replaced that circuit with a copy of the circuit used for the crank input.

Both cars work flawlessly now, when one car would lose sync every 5 or so minutes, and the other every 20 minutes. So I suggest that everyone uses this on their builds.

A datapoint -- I've been running with dual optos since I built my MS2 in fall '08 and have never had a sync loss issue on either the 1990 or 1996 engine/CAS.

I (obviously) think that running the dual optoisolators is a good idea as well.

Im running dual optos on mine, but never had 1 issue with the standard single opto input on any of the CAS MS2-MS3 setups I've done.

I had sync issues with just 1 opto too, have always run 2 optos since and zero issues

Anyone care to update the stickies?

Did you guys have to do anything out of the ordinary to get the opto on the second trigger to work? I tried running a second opto on mine but could never get it to sync. I installed the basic trigger, it synced, fired right up and ran perfect. I'm wondering if I ended up with a bad opto isolator from Digikey.

you just duplicate the circuit that's built in.

http://msextra.com/doc/ms2extra/Igni...V_V3_Input.GIF

http://msextra.com/doc/ms2extra/Igni...dCAS_Input.GIF

http://www.boostedmiata.com/gallery2...2/DSC_0117.JPG


I run the second trigger opto, but like I said, I never had an issue without it. I installed it trying to tract down a misfire I having on MS3.

Ive probably done 20 or so v3.0 boards with MS2 on 90-97 cars without any sync issues without the second.

Yep, that's how I had it hooked up. Double checked it 3 times too. Input to the opto was good (power and ground) but it didn't ever seem to output a signal. Wierd. I must have gotten a bad one. I'll have to get another and try it out.

Thanks!

Reverant,

Did your original build include the cap mod? The cap is too large for MS2, which triggers off both edges.

Ah yes. The few MSPNPs I've custom converted to MS2, I've removed the 2nd trigger cap. So far, I haven't seen any sync loss issues without it, though it's possible it might need a small cap.

The 2nd opto method should work well too.

I tried with and without cap, with cap it lost sync above IIRC 4k, without cap it never sync'd

No. Just the 470R pullup to 5V.

How was the crank input set up? It needs to be inverted with that particular cam input setup.