Lagontinas

Hi guys,

I'm running a strange issue with my MS on my 96 1.8 NA.
For reasons I can't figure out, it's starting to misfire a lot on idle.

Here's the setup, I will try to make it as detailed as possible:

- MS2 with V3.0 PCB and adapter harness, built by myself (3.4.2 MSExtra firmware)
- MSPnP basemap from DIYAutotune
- Innovate LC-2 wideband controller (directly wired on adapter harness)
- stock NA 96 1.8 engine, injectors & ignition
- injectors running batch, not sequential

I've been reading lots of documentation on how megasquirt works, tried to check every important parameter in tunerstudio, with the help of tunerstudio and MS manuals.
But, I'm stuck, and I couldn't find someone with a similar problem by searching on the forum or the whole interwebz.

Timing has been set and rechecked many times with the trigger wizard and timing lamp.
Req_fuel at 12.2ms calculated with TS (1840cc engine and 254cc tan-top injectors)
Initial value of injector dead-time was at 1.2ms, lowered at 0.9 (recommended by TS) after reading carefully tons of posts.
Standard 1.8 coils, dwell setting at 4.5ms running and 7.5ms cranking (thanks to DIYautotune tutorial).

Engine is running fine with no misfire at around 12:1 AFR during warmup.
MAP is around 28kpa during idle.
And then, at running temp, it starts misfiring if the AFR is higher than 13:1, exhaust smells unburnt fuel in any case.
I tried to follow idle tuning tutorials found here and there : unplug the IAC valve, adjust idle valve screw at around 900rpm and tune the idle cells on the VE table. But every time my AFR is higher than 13, it misfires again.
Timing is set at 12 on idle cells.
No EGO correction.

I saw someone having the same issue because of a pinched vacuum hose going to the map sensor. Checked it, hose is ok.
I also went back to stock ECU/O2 sensor to check anything related to engine components, worked fine, no misfire. Then reinstalled everything and re-calibrated the LC-2, misfiring again.
I checked the AFR offset between the MS and the LC-2 with its dedicated software, everything is okay, no offset.

I hope it's only a matter of some parameters, I'm sure I'm missing something.
Because of the bad idle, I don't want to try to tune the rest of the VE table and mess everything up.

You can find attached an idle log and my .msq tune file

Thank's for the help, feel free to ask if you need more information !

Bronson M

iTrader: (1)

You didn't say how pronounced the misfire was, if it's relatively mild and just something you can hear but not necessarily somthing you feel then it's probably the fact you're running batch. Since the fuel is sitting on the back of the valve atomization is poor. The fix is to simply richen it up till the missfire goes away. I find I need to be richer than 12.5 to 1 to quite a slight misfire at idle.

They say you can run both of 14 to 1 with sequential, I'm about to convert so I'll let you know.

Lagontinas

Thank's for your answer.

Indeed, at around 12 AFR car is running okay, a very few "pops" (not in the exhaust though, you can see the engine bumping), but smells unburnt gas.
If I go above 13, engines starts to misfire more and more, it vibrates and sounds like hitting the rev limiter. Above 14, AFR gets very unstable and jumps to 15, so definitely too lean.
Is it okay to run idle at 12 AFR ? Sounds super rich to me...All tutorials I've been reading were talking more about 13-13.5 afr at idle, not lower.
If 12 is okay, i'll run 12. All I want is a smooth idle so I can continue on tuning, why not switching to sequential later though...

Bronson M

iTrader: (1)

The miss I'm talking about is just an audible random pop through the exhaust, no visible shaking of felt vibration. Yours sounds more ignition related, the hardest thing for your ignition system is idling and wot. I've seen a lot of ignition issues sure up at idle and be fine otherwise.

I'd keep digging...... Sorry

Lagontinas

Hi,

Don't be sorry, I will keep on investigating ! I also took your advice and checked the ignition.
I first checked on table if the spark output system in the megasquirt was running okay, it was. (I built it as presented on the miataturbo tutorial Megasquirt 2 Intro - Miata Turbo FAQ ) Output was visualized with an oscilloscope, pulses were ok.
Then, I ran the same test on the car, engine running, once with the megasquirt, the other time with the stock ECU. Measurements were performed directly on one of the coils connector.
I noticed a big difference between signals : spark outputs on the megasquirt were very noisy.

Here is a capture of a "noisy" pulse (they weren't all like this, but there was enough to sabotage my ignition) :



And to compare, a pulse generated by the stock ECU :



I also checked grounds, I could find only one ground post on the engine, next to the throttle body, and I already cleaned it up few moths ago. I don't have the two ground connectors next to the coils and the back of the intake manifold.

I checked the same signal on the adapter harness, pulses are looking the same as on the coil connector but signal is far less noisy (sorry, no picture).

Here is a comparison between the megasquirt signal vs stock ecu signal :

Megasquirt : (peak voltage 2.5v)



Stock (peak voltage around 3.2v) :



All measurements are performed at idle, with warm engine.

Now I know that it's definitely spark related, I know where to look at. Lots of people have modified their megasquirt the way I did, hopefully I can find someone who had the same issue and solved it.

Thanks !

Adrian