random "hickup"
 

i really dont know what to think about this. my car has a completly random hickup, enough to see it come up on the tach, but i havent been able to notice anything in a datalog. it is completly random, will happen partial throttle and also at WOT. any ideas on what what to look for? i will go over all of the ground, but besides that, im clueless.

also, i have the solid MMR motor mounts, ever sence i put them in, the guages shake a ton, the tach is by far the worse, speedo is the least. is there anyfix for this?

So the MS isn't spontaneously resetting then, correct? (Shows up as a horizontal red line in the log)

Install softer motor mounts.

nope, the MS is not resetting.

i need to hop on getting this thing in tune better anyway, i will post a datalog and my MSQ here in a day or two

MSPNP or DIY MS?

its a DIY, i built it

Although it seemed to affect primarily HR users, there was a fault recently discovered in the CMP (secondary) CAS input which caused noise on the input and resulted in exactly this problem.

The solution was to lay a .1uf capacitor between pins 11 of the CPU socket and ground. Read all 'bout it: http://www.msextra.com/viewtopic.php?t=26727

Might be worth a shot.

It's very likely noise on the 2nd trigger causing an occasional misfire. Check out this thread for more info: https://www.miataturbo.net/forum/sho...t=14871&page=2

Or this thread for all the technical details- http://www.msextra.com/viewtopic.php?t=26727&highlight=

But if this is it, to fix it, put a .1uf capacitor between JS8 and GND. That's it!

heh... I took to long to dig up those links ;)

BTW-- it helps non-HR users too... the 90-95 cars aren't as bad about this, the 96-97 cars had a noisier signal, but this solves it across the board...

Curiously- everything I've read indicates that the early cars primarily used an optical CAS and that the hall-effect unit was not introduced until later. My '92 has a hall-effect sensor, so perhaps the correlation has less to do with year of car than with sensor type.

I can't say whether this mod solved any particular problem for me as I did it prior to installing my MS.

did a little tunning this weekend and its completly random, it has no pattern at all. here is my MSQ. i will also try out that cap mod

My 90 with a MSPNP had this and "random hiccup" describes it perfectly. I fitted the extra capacitor and it cured it completely and also seems to have helped crear up a light throttle hesitancy. It's well worth doing for the 12 pence it cost me.

Folks, This is great info! My 94 has been suffering with the same problem...

I'm in the same boat... guess I'm heading to radio shack this week.

got the .1uf cap, put it in, went for a quick 5 minute drive and NO HICCUPS!!! thanks a ton guys

thank god that problem is fixed... no more hick-up... now people don't make fun of my car. As much.

Sorry to bring a thread back from the dead, but I just wanted to add that the .1uf cap works great!!! I was having problems with a big miss at idle and every so often it would miss under WOT BAD. I put the cap in and like magic it all went away.

Thanks for the info
:bowdown:

Any reason why adding a .1uf cap where you describe would harm an AEM EMS? I don't know what adding a cap to ground does electronically, but could the AEM EMS have some sort of wiring that would go ::FIZZZ:: if a cap was wired there?

My AEM does this too. Tach drops for a split second, ~0.1sec spike shows up on the RPM datalog. Mostly fixed when I went to the 1.8 but still there a little. If 12cents CAN'T HURT i'll try it. Any ideas?

its really just a filter, you could even try a .01 or .001uf cap if it filters the tach signal completely.

The circuit is more than just a cap though... it's just in our case, the resistor that was needed was already there.....

Here's the full circuit. Ignore the one on the left as it's just an example of what didn't work. The circuit on the right does work... You'd want to make sure there is a resistor in between the CAS 2nd trigger input and the processor, and right in between those two put the .1uf cap to ground.

http://www.diyautotune.com/images/fo.../fix_schem.gif

Note you shouldn't need to worry with the pullup to 5v as that should be taken care of already...

Scott, is this something i should do?
you know im clueless when it comes to this stuff
thanks