its either they are leaking or you have completely bogus cranking settings.

Hi all, digging up an old thread I know, but I have been trying to fault find the popping fault on ECU power on, with my MS2 V3, 1.8 1994, standard coils, wasted spark.

Came across this thread, full of hope, opened my MS2 V3 to already find Joe's circuit in place on the two ignition circuits. Spark invert is on (going high). Car runs fine, just intake manifold backfires on turn of key. Not all of the time, but regularly. Normally worse on hot days. Can happen with engine cold or hot though.

I have previously changed my injectors, still popping. I notice that when I turn the key to ign the tach needle does one small bounce, so the coils are still firing for some reason. Going from this thread, with Joe's circuit, this should not be happening.

Electronics is my weakness, so I have a couple of questions to people more knowledgeable about the Miata's ignition system.

1) Are the coils able to hold charge in them when the car is off? i.e I turn car off but unluckily I have turned it off during the charge phase in the cycle for one of the coils, but before discharge. This charge is then held in the coil until the ign switch is turned, MS boot time means 0v signal is provided to coil, and it fires the coil. Extreme long shot but I am starting to clutch at straws.

2) Is this possibly a symptom of my coil pack starting to die? Seems a bit odd as I would expect to see other symptoms, rough running etc, but I have heard they can fail in weird and wonderful ways.

The issue happened very occasionally last summer, but is a lot worse this summer. The car now regularly blows the vacuum line off the FPR, so I am anxious to solve this issue to avoid any further damage. The fact that it seems to have got worse is swaying me towards the failure of a component, rather than the initial setup issue.

Any help welcome!

Tom

Hi Everyone, i know this is a stupid question but I need to ask.

This whole inverted signal then uninvert (double inverted?) and then set CPU to invert/uninvert output has my brain all conjumbled. I am not a smart man.

Can someone please tell me: if running an ms2, stock coils, and the Joe Perez spark output circuit from this thread, in Tunerstudio should the "Spark Output" setting be set to "Going High" or "Going Low"?

I'm not sure if the software has been updated with time and the verbiage has changed, but this option in Tunerstudio is no longer "spark output inverted = yes" and my dumb brain can't translate the old to the new. A simple "yes use going high" or "no you idiot use going low" will suffice.

Please halp me.

are you trying to run a MS1 unit or something?


inverted = yes = going high

He says MS2 in his question.

Yes it's a DIY MS2 unit. And thanks for the clear cut answer, this stuff is very confusing to me. From what I can understand, the stock ms2 spark output is already inverted but Joe's circuit then un-inverts said signal but the ECU would still see that as "inverted". At the same time with the new nomenclature, technically the coils don't fire when the spark output is "Going High" but that is what we need to tell the ECU as we have inverted the signal. Am I understanding that correctly?

If you'll bear with me, I am currently working on installing the ms2 unit into my car now that I have a few weeks off of work (in between jobs atm). The car is a '99 all stock (nb everything) that i'm attempting a ms2 parallel install with the stock ECU. As of now I have the system configured so that the stock ECU retains control of the tach, alternator voltage and IAC. I've now installed the system into the car and it is running however, the car idles very high, like 2000rpm. Because of this I haven't officially synced the ignition timing as i can't get the car down to proper idle range though from what I can tell, at 2000rpm the timing matches what the ms is commanding.

My question is, what would cause the idle to be so high? if the stock ECU is controlling the idle valve and receiving all required sensor inputs from the vehicle, shouldn't it retain the same idle as full standalone stock ECU? When I revert back to the standard ECU the idle is fine, around 800rpm. The other oddity is that the AFR is very high, high 19s or so though I don't know how trust worthy those numbers are as I'm still using the stock narrowband (wideband on order). Any ideas how to get the idle down? I'm wondering if it has something to do with a gunked up throttle plate not closing all the way. The stock ECU may have learned around it but the ms is seeing my throttle position as closed and offering less fuel to the system when there's a huge vacuum leak through throttle plate, which would also explain the very lean conditions. I will pull the throttle body off and have a look. If anyone else has any ideas please let me know. Thanks!

Timing has a huge amount to do with idle, as well as the IAC. You can still lock your timing at 10 degrees and sync timing at 2000rpm.

Hi Curly, you're right, timing does seem to have a huge effect on idle. I did as you suggested and synced the ignition timing at 2000rpm and in locking the timing to 10°, the idle dropped about 300rpm. However that did not resolve the problem.

I did pop off and clean up the throttle body, nothing too excessive as far as build up. It also seems my parallel install may not be fully functioning, i am not getting a tach output and I think the alternator is no longer charging the battery. The battery voltage seems to fall fairly quickly from 12.4v to ~11.2v or so while the car is running and It seems like the idle is increasing in speed as the battery drains. I wonder if this is then affecting the ignition dwell from the dwell battery correction settings?

Just random thoughts, appreciate the input.