MS3X Timing / CAS Issue
 

I have an MS3X I used on my old NB Miata. Now I'm trying to use it on my 94. I created a new patch harness following Braineack's diagram. My MS3X is fully assembled so I have R52 maxed to 100k and I manually added the 5v pullup for the crank by jumping a 5v near the proto area to VRIN with a 1k resistor. I also have the 12v pullup (s12c to JS9) jumper in place and the flyback mod setup. I'm using Braineack's base tune with no changes other than setting the timing to fixed and turning off the wideband EGO control (don't have it setup yet).

I'm getting a weird issue. The composite log looks good. Testing with a Jimstim looks good. The car starts but idles and revs poorly and dies (or nearly dies) when the revs drop after blipping the throttle. I get quite a bit of fuel smell (no surprise with the way it seems to be running). I don't seem to get any sync errors though. When watching with a timing light the timing seems to jump around a few degrees and when revving the timing starts to jump extremely far off. Just out of curiosity I threw the timing light on plug 2 and would frequently see the it fire just before TDC (same place as plug 1). I have no idea what's happening and I'm wondering if my patch harness or something else maybe has some interference or something?

Below is a bad timing light video. Here's some crappy pictures of the composite log idling and in log crank&cam mode. Attached is log starting and revving a little bit and also a composite log from the same time I think.

I've been trying to figure this thing out forever and wanted to see if there's something I'm missing before I try remaking my patch harness or just folding and buying a PNP setup...

Timing jitter. It happens, only so much mechanical rigidity in a timing belt. But it's also not likely the cause of your problem. My guess is either acceleration enrichment or idle dashpot, but tuning idle is usually done after you've got a halfway close fuel map.

I've seen similar timing shift issues on VR sensors with incorrect settings. Why did you go this far and not attach your tune?

I don't understand what you're saying about the composite log screen caps. The bottom one is littered with sync loss AFAIK.

I think it’s beyond typical timing jitter. It’s certainly much more stable with the factory ECU in place.

AFAIK it always shows sync errors when in “log crank and cam” mode. When in 4G63 mode and actually running it does not have sync errors. Here’s a direct link to the tune. As I said, I’m using Braineack’s base tune with no changes other then turning off EGO control and setting it to fixed timing.

https://trubokitty.com/assets/tunes/...4-97_1.4.1.msq

If we could trust you've done everything right to this point then you probably wouldn't be here asking for help. Please attach the actual tune you're using to run the car.

I would try switching input capture mode to falling edge.

Added actual tune to OP. The car will not start with falling edge. Rising is correct AFAIK and the composite logs look correct from others that I've seen.

Your composite logs don't look right to me. Look at the timing of the cam and crank signals. They don't line up correctly. Here's a log from mine.

https://cimg0.ibsrv.net/gimg/www.mia...ef6f99d7c9.png

You're definitely right. Looks like the downside of the larger cam signal lines up perfectly with the downside of the crank signal on yours. My downside of the larger cam signal comes just a bit before the drop of the crank signal. Now the question is what could cause that? The CAS sends both signals, correct? What would cause them to get slightly askew like that?

So in the meantime, I was leaning toward the slight difference in the cam/crank signal being the issue and went back and manually set all the variable resistors using a volt meter, where previously I just followed steps and did it by number of turns and I think I ended up changing a few quite a bit.

So then I went back and looked at the log and the MAP reading is constant the whole time. So I verified I had a good spot on the manifold and even remember, when initially setting it up, verifying the line I ran had vacuum with my finger. I then checked the MS and tuner studio to make sure it was properly reading vacuum and pressure and it was.

I hooked everything back up and now it has no issues and is running fine with no timing issues. I was troubleshooting this issue on/off for months across and even tried it in two identical cars and I can't imagine it wasn't reading MAP every time. Whatever the case it is working now. Now to get my wideband back in and then throw my turbo bits back on later.

Thanks!