I've been getting the random tach signal dropoffs that some other people have complained about:

https://www.miataturbo.net/megasquirt-18/ms-issue-question-cas-going-bad-42483/
https://www.miataturbo.net/megasquirt-18/ms-missing-issues-43989/

It only seems to happen while cruising and the longer I've been driving the more often it happens. I believe it started about the same time I put in my Toyota COPs. Though after I took the COPs off, it still happens. Wtf. I have a Braineack MS build from a year or so ago, so I believe it should have the capacitor that is supposed to smooth out the CAS signal.

Here's my checklist of **** to try/already tried, and some screenshots of the events. Am I on the right track?

[x] Problem with the ignitor? -- Reverted back from COPs to stock. Always careful when flashing firmware
[x] New plugs (gapped down to 40) and wires
[x] Reflashed firmware
[x] Over Run only starts under 28 KPa, events happen >40
[x] Put the hotter plugs back in
[x] Replace connectors at the battery and comb the car for loose/disconnected grounds
[x] Check for the .1uf cap between JS8 and ground on the MS http://www.boostedmiata.com/MS/1uf_cap.jpg
[x] Unhook FMU and run no boost, see if anything changes
[x] Turn overrun off
[ ] Check for ghost of Hitler haunting CAS
[ ] Cuss and urinate indiscriminately, buy a Prius

 

Well I put the old plugs back in, since I started getting the symptom at about the time I replaced them. No luck. I'm dyin' here.

Since I'm getting a tach spike, I think I can assume that it's not my ignition system acting weird, it's got to either be the CAS signal or something weirder in the MS. If I crack open the case and see that Braineack did put that extra capacitor on my MS build, I guess my next step is to either clip the CAS wire from my harness and run it shielded through the firewall, or try to learn wth is up with Joe Perez' 36-1 wheel mentioned here: https://www.miataturbo.net/megasquirt-18/losing-spark-tach-5000rpm-under-load-36299/ . My symptoms seem different though, since it happens when I'm easy on the throttle (usually rolling gently back onto it), and I haven't noticed it on WOT.

 

Updated my checklist in the original post.

I checked and the .1uf cap is indeed installed on the MS, so that ain't the problem. Bought some shielded wire to run a tach signal through the firewall, so I'm hoping the noise is from somewhere in the harness and not near the CAS itself, but I know exactly jack and **** about electronics in general, so maybe I'm on the wrong track, yeehaw.

I'm so depressed. I haven't actually enjoyed driving a Miata in about two years, and been owning them for 10.

 

Try adding more grounds, or clean up your grounds. A faulty CAS could be a problem too.

or

Try abe's NB crank circuit. You have the ability to change the capacitors on the signals, and the NB's crank circuit is a lot better than the MS's stock one.

EDIT: Just realized you live in the bay area. WHere? PM me, you could come by my place and I could try to take a look at it.

 

I have the a similar problem, mine is very random it can happen anytime. I'm looking forward to your end result with the shielded wiring.

 

I have a similar problem. It usually only happens on highway cruise. Logs say the same thing. Ive ignored it. I want to see your results!

 

I wussed out on the wiring, since it seems like it will be a big PITA and might not help. I want to try Abe's NB crank input, but I haven't been able to find enough info on how to wire it in, or what the latest version is, etc. The big thread for it is here: https://www.miataturbo.net/megasquirt-18/abe-jasoncs-nb-cam-crank-input-circuits-25789/

Marc D is a local and I've been trying to hook up with him for some advice, but we're both busy dudes.

 

If it was a misfire due to things like the spark plugs, coil, etc., then the logs would still show a normal RPM reading, and maybe the only way you could see the misfire was a spike in AFR.

The spikes on your RPM log are acutally a sign that the CAS might be starting to go out, or in the least it's getting signal noise and getting the MS confused. Whatever the fault, the fact that the MS is logging the spike tells me that that's the signal it acutally received from the CAS and it logged it.

 

I still have this issue and I have built the circuit for Abes mod but I haven't installed it. Hopefully I will do it this weekend and report the results

 

I never had a problem on the stock ECU, but maybe the MS is more sensitive. I have a friend who has another 1.6, so I'll swap CASes with him and see if that helps.

Did you build it into a little case outside of the MS, or did you squeeze it onto the proto area? I am a total hamfist when it comes to electronics, plus I have just enough knowledge to be a hazard.

 

Watching to get a fix for mine too. I've always had this problem and its getting worse to the point. I've chased wires and grounds with no success. I guess its time to replace the CAS.

 

I built it on a separate bored... I am going to try to mount the board to the inside of the case if there is room.

As other people mentioned, I have ZERO issues with the stock ecu. I recently had it in to pass emissions. I also tracked down grounds, added a bunch, and cleaned up the wiring to the CAS all with no luck... I think this circuit is needed rather than a new CAS in my case... CAS is plan B

OH and FYI mine has gotten so bad I cant even autox. It will randomly get bad signals and activate my rev limiter when I am beating on it... Logs said 10,000 RPM +... Frustrating to say the least.

 

what is abe's mode? his tach input circuit?

 

Yea look at the link the op posted.

I think brain just needs to make us all free ms3x's lol

 

I had similar problems and the datalog showed some noise in the battery voltage, clt temp and MAT. I then did some searching and found this link link very useful. I did the capacitor on the boot jumper mod and it fixed all my misfiring issue. The noise in battery voltage logs also were mostly gone. Hope this helps.

-Raj

p.s. I am running Abe's NB input circuit.

 

are you running lowz injectors? Did you have this problem even after you did the input circuit?

 

Yes, I am running low-z injectors. I started with Abe's input circuit. I used his 99-00 adapter board and modded it to work with my car. I have never used any other input circuit. You can see from the discussion on msextra that people using high z injectors have also seen this noise problem.

 

WOW. Looking at my log that I took of the problem I see HUGE fluctiation in my CLT. ... like 140 to 180 back and forth. My battery voltage has noise too but it only fluctuates .2V either way.

Time to do the cap mod!

Can you please explain exactly what you did to stabalize your signals? IK you have MS2, we are all running MS1

 

Any updates on this? I've been having similar problems

 

low ohm injectors?