MS1 random cut out while cruising
 

Afternoon folks, I've been having a bit of a problem that I believe is Megasquirt related. While cruising, it often has a misfire that jerks the car, which is incredibly annoying. It seems to be accompanied with a massive RPM spike and the wideband reads a lean spike, also. Here's the specs of the car:


'96 Miata
MS1 3.0 board
T25 running 8 PSI

I've wired in the .1uf capacitor, and think my CAS is good, but I've heard that the CAS can have interference with other high voltage wires? Also, either I'm paranoid or I notice it more often, but it seems to get worse when I have a passenger in the car (MS is behind the passenger seat) or when it rains.

The reason that I suspect it is the Megasquirt is because I've had these symptoms with two different engines.


I've attached a log file with a few of the events. The first time I hit the spacebar in the log I believe was a fluke, but the second two times were definitely misfires. The last one probably being the best representation.

Subscribed. I have looked into this issue before with not real findings. It happens on highway cruise to me quite frequently. Does not happen on the stock ecu. I've played with plugs, coils , grounding , capacitor, etc with no luck. Finally just learned to live with it. I did buy another CAS to try next spring though.

I think I know where you got that CAS.... lol

I'm pretty sure you got the one from my replacement motor, and I swapped my old one over, though.

Haha damn. So so did you try the CAS I have?

Don't think so. I think I swapped it out because I thought it was bad (car wouldn't start), only to find out that I had another problem entirely. (I'm a dingus and had some wires backwards)

bumping with cat pictures to please the miata gods

https://www.miataturbo.net/attachmen...ine=1385073271

Considering going to a crank trigger wheel setup. Looks like Joe Perez has used it to help get rid of his 'misfire' with good success.

https://www.miataturbo.net/megasquir...ss-last-20241/

I understand that I should need a trigger wheel : 2000 Mazda Protege Parts - Online Mazda Parts

and a crank angle sensor from an NB.


Still a bit unsure on what all is needed to take the cam angle sensor completely out of the equation, but still searching.

240 are you using MS1? Would you mind posting your tune? Trying to find some common denominators

You need to make another optoisolator circuit for the 2nd input on the cas. Info is in here:

https://www.miataturbo.net/megasquir...tor-ms2-71250/

I haven't had a single dropout in the past year since doing this mod.

Is this the diagram you used to wire yours?

https://www.miataturbo.net/attachmen...-dscf6117g-jpg

Also, with MS1, how would I know I'm getting sync loss?

Also, after looking at a few logs Ive noticed that the cut out is not always accompanied by an rpm spike or drop. Could this be sync loss?

The diagram of the circuit I used is on page2 which I can't access for some reason. says something like prefetching is not allowed. Tried in another browser with no success.

This one?

MS2-Extra Miata 4g63 Manual

This would be different for a MS1 though, correct?

Like this https://www.miataturbo.net/attachmen...dcas_input-gif But Pin 2 comes in from the IAC1A on the harness If you set your megasquirt up like 99% of the people on here. The output goes to JS10 on MS2 I Dont recall what pin it was on MS1 but its the pin the the .1uf capacitor goes to. EDIT: It appears to be JS8 on MS1.

Yeah MS1.
Ill try to remember to boot up my tuning laptop and grab the latest tonight.

I can understand most of that diagram, but the optoisolator part confuses me a bit (blue circle part) what are pins 1, 4, 2, and 5?

Proof I am a slacker...

https://www.miataturbo.net/megasquir...r-input-70794/

(I did actually try joes input at one point but the car didn't crank. I probably screwed up the circuit so I just said screw it and scrapped that idea)

I should build in the opto circuit this winter.

Is this my answer?

https://www.miataturbo.net/attachmen...ine=1386715987

yea the 4n25 opto like This

I, too, have the same issue.

MS1 v3 DIY built myself following the original thread.

I am getting dropouts around 3.5k RPM, so basically highway cruising.

I was able to follow the instructions pretty well to build the MS board as the picture tutorial was great. I tried to read the schematic but I am not 100% sure as I do not know symbols for everything. I used my mad MSPaint skills to add on to DIY's mod photo to show how I would solder in this 2nd opto circuit.

Can anyone confirm that this is correct?

Gotcha. I ordered a few, and the other components you ordered in that thread from digikey.

Pro tip: apparently the dot on the top of the opto designates the #1 pin

Edit: kero that looks right to me, but my opinion is incredibly uninformed. Maybe someone with better knowledge than I can chime in

Looks good, Just remove the original 2 resistors (Red Lines) that go from IAC1A to 5v and js8. I build my circuit on one of these: Dual General-Purpose IC PC Board : PC Boards | RadioShack.com and mounted it in the case.

Is there a different optoisolator I could use that I could source from Radioshack or Fry's? I tried searching 4N25 on their sites, but nothing came up

I think there is a 4n25 already on the ms3.0 board. Not sure if you could use it or not.

the 4n25 on the ms board is used already for the primary input from the CAS. what you are esentually doing with this mod is duplicating that circuit for the sencondary input from the CAS. Digikey is fairly quick with their orders, I never looks elsewhere for the 4n25.

Is there enough room to mount one of those? (I'm using the stock DIY case)

That seems like a neat way to do it

edit:

https://www.miataturbo.net/attachmen...ine=1386811847

Parts list of what I just ordered

My MS has been changed so much over the years I gave up on my sloppy proto area. I just recently used that radio shack board in an external enclosure and just popped the necessary wires out of my MS enclosure to use for VCCS Sucks, but it was the easiest way.

Mine fit fine in the stock case. I cut the wafer in half though as you only need 6 slots of it for the 4n25.

How did you mount it? screws? doube sided tape?

On the back side of the board using one of the leftover holes on the heatsink, using one bolt and a little bit of hot glue to keep it from vibrating around.

Wired mine in the proto area using kero's picture. just took it for a (short) drive down the road. Too soon to report no problems, but it runs, which is good.

Nice. I will do mine this winter. I moved to a new shop last night. Driving on the highway @ 3400 for 20 minutes in 20*f weather it happened about 4 times.

Sweet. My optoisolator should be here Monday, hopefully I can do mine on Tuesday.

I just installed my circuit. Still had the same issue occur on the highway. Could my igniter just be taking a shit?

I've noticed that I'm still getting the misfire as well. I took a log and haven't seen an rpm spike but still had the stutter, albeit seemingly less often. I'll post my log up soon.

Mine still shows in logs. I've read somewhere that a failing ignitor can cause this. Do you have a spare to test? I don't have another to try. I'm kinda dumbfounded

I don't think 1.8s use igniters like 1.6s do. Correct me if I'm wrong. I'm going to try to post my log up tonight.

Yes and no. They are just built into the coilpack. I wonder if coils themselves could be weak. I think I will try upgrading to Toyota COPs

Here's my log

I did that with no success. Still had misfire after.

So what's left then? lol

CAS going intermittent?

My plan is to do the second opto isolator like you guys did. If that fails, I'll swap CAS, If that fails I have exhausted all my options other than swapping out my ms1 or changing to a trigger wheel.

Wanted to add to this thread. I have suffered from this issue on my fathers 95 from day 1.

I have built the optoisolator circuit to no avail.

It is an extremely long story but when the car had MS2 on it, it had no issues. After I converted to MS1 this is when the symptoms showed themselves. I feel the optoisolator circuit did indeed "help", but not cure the issue.

Seriously though, with how easy it truly is to change to MS2, it doesn't make much sense to continue to run MS1. Unless you already have a spare CAS, spend the money on MS2 and upgrade what you have.

While that might work, it's more of a workaround than a fix. To me, I don't need an MS2 just yet, so I'm not too eager to upgrade.

I've considered going MS2. what all is needed to convert?

swap in the daughterboard and redo the inputs?

Bringing this back.

I cleaned all grounds and ran new one to the ecu from head.
Upgraded to Toyota COP setup.

Problem still persists, though it seemed like it was not as severe/often, though I only drove it today.

So I suppose the only thing left is the CAS?

CAS or upgrade to MS2. I may upgrade to MS2 with my income tax refund. I'll be sure to report back if I do.

Is the CAS known to go bad at all? (i haven't really seen much info on them going bad)

Is there anything to clean in them?

Did you try Joe's circuit?

https://www.miataturbo.net/attachmen...-schematic-gif

No I have not, I did try the 2nd opto circuit posted in the 1st page.

I tried Joe's circuit and the car didnt start, but I probably messed something up. That was 2 years ago and I just swapped everything back over immediately.

I am going MS2 in the spring, using the standard inputs. If I have issues after that I will continue investigating.

I wonder if switching to a trigger wheel setup would fix this

I think that is what Joe ended up doing. For me that is an ugly option as I need to be able to swap back to the stock ECU easily for OBD2 emissions here in CT. I don't want to have a secondary harness and a bunch of shit to change.

It was, back on my first Miata and my first MS1. I now know more than I did then, and I would not recommend this as a fix for a finicky CAS.

In my case, the CAS worked fine on the stock ECU, but not the MS. That alone tells you that the MS was the problem, but I really wanted to build something on my new lathe, do I solved the problem the extremely hard way.

I would use a 2000 protege 36 to 1 wheel and fit an NB (99+) crank sensor (do those bolt straight onto 1.6 oil pump?)

So I don't think it would be too hard nor crazy expensive

Swapped the CAS for another one I got with a used engine. Still no change. Also soaked the board in alcohol to clean all the flux off (i never did the first time around as it was supposedly no clean flux wire). Still no change. I'm at a a loss here.

It sucks this didn't work out for you. It worked out great for the 2 MS2's I tried it on. Maybe having MS2 made the difference...

Switched to 36-1 and a Hall sensor and have more noise than before.

If I rev the engine and hold it around 5k it will have RPM spikes in logs to 10k.

Activates rev limited/retard resulting in flames lol.

Installed a shielded wire on the sensor, improved things but still spikes.

So basically I've tried:
Switched to COPs to eliminate coils/igniter
Switched to a new CAS
Built second opto isolator
Cleaned the board
Added more grounds/cleaned existing
Switched to 36-1 with a Hall sensor

So the only thing left original/unchanged is the MS1.

Will an MS2 card do it or is something else inside my MS messed up? Ahhh such a headache

edit:
said fuck it, summer is near, ordered MS2 daughter board

I hope upgrading to MS2 works for you, I know from experience how annoying it is to drive acting up like that.

Any luck, Kero? I just freed up some money and am considering moving to an MS2

Not that it would make a difference at this point but the capacitor you have show is .1uF, but looks like you ordered a 399-4326-nd which is 10,000PF or .01uF. .01uF is also what's shown in the msextra docs. I'm looking to cure the sync problem myself :)