Slight misfire after throttle is pressed

[Reverant]

Hi,

I (and a LOT of Miata owners) have this issue, where usually after decel and then resuming the throttle, you can feel a small misfire/stumble 0.5-2 seconds after the throttle has been pressed.

It doesn't happen every time, so there's a bit of a randomness to it.
It doesn't happen to steady-state cruising or when you are WOT.
It is there in both 4G63 and Miata 99-00 wheel patterns.
It is there in both MS2/V3 boards and Microsquirt modules (ie DIYPNP)
All of the units affected are running TPSdot, not MAPdot.
It happens a lot less if I increase the TPSdot threshold to values greater than 120 or so, but then the car is bucking and hesitating when trying to get the car moving in 1st gear - ie low TPSdot areas.
All of the units affected are running sequential injection - one unit that I tuned that was running batch did NOT exhibit this problem in some 100 miles that I did while tuning, the owner also didn't complain.
All of the units are running 3.0.3u and 3.0.3v.
It still happens with EGO turned off.
It's significant enough to actually feel it either as a driver or as a passenger, yet when I look at the logs, I can't see it in the logs, even if I mark it a couple of seconds after it happens by pressing the spacebar.

Any ideas?

Thanks,
Dimitris

[richyvrlimited]

Just chiming in to confirm I'm suffering too.

[jsmcortina]

As a wild guess - injector timing?

James

[ol boy]

You say after decel? How much decel? My own car has the same stumble but I'm running a wet intake so all the fuel that was on the intake runner walls gets stripped and once the over run turns off (injectors back on) I run really lean for a few seconds as the walls re-wet. I've wondered how much affect over run would have if I was running the motor hard at a road course or something being on and off the throttle so much and having to re-wet the intake every time I'm back on the gas.

Just an idea. Later Ryan

[Zaphod]

I have the exact problem - I even get the stumbles at very steady cruising conditions sometimes.

I already had made a thread about that here:

http://www.msextra.com/forums/viewtopic ... 70&start=0

I also have the stumbles when simply accelarating after an deccel event - no big stump on the throttle just normal steady increase.

[CRAIGO]

Just chiming in to report that I have the exact same issue. Mine can also occur during steady-state low rpm/load cruise too as Zaphod stated.

As mentioned on other boards, my occurance is usually 3 times per week MAX. Some weeks it doesn't occur at all. Pressing space and analysing the logs after the occurance shows nothing unusual.

The feeling is of a slight misfire/ECU burn command and only occurs when lightly on the throttle. I've never had it happen while WOT or at high RPM.

[Reverant]

As a wild guess - injector timing?

James

It's set to fixed timing and -350*. What exactly are your suspicions?

[racingmini_mtl]

If all of you who have this issue can post an msq and a log showing where this is happening then it might be possible to see some pattern. Without this and without being able to reproduce this on the bench, it would be very difficult to see if there is something in the code that can cause it.

As for injection timing, it may be that you simply need a different timing for those conditions. A fixed value will likely not be the best for all conditions so you could try changing it to see if it has an impact. And use the table if it causes issues with normal operations so that the changed value only covers the region where you have the stumble.

Jean

[jsmcortina]

As a wild guess - injector timing?

James

It's set to fixed timing and -350*. What exactly are your suspicions?

I was wondering if that was the "worst" injection angle for those conditions. With batch-fire some cylinders are "right" and some are "wrong". With sequential you can configure them all to be wrong...

Varying injection angle has a big impact on idle smoothness on my V8 (with MS3) so it could easily have a negative impact as you are seeing.

James

[richyvrlimited]

I don't think it's that, mine is set with the timing table populated based on a method of tuning posted on here and I still get this 'missfire'

[jsmcortina]

I don't think it's that, mine is set with the timing table populated based on a method of tuning posted on here and I still get this 'missfire'

If you've eliminated that, then good. As I originally posted, it was a wild guess that was at least _possible_.

James

[muythaibxr]

Have you tried using EAE instead of or in addition to normal AE?

Braineack reported success with EAE on an ms3.

Ken

[richyvrlimited]

Me personally, no though I do want to as overlaying AFR target and actual traces in TunerStudio doesn't look great ;)

Unfortunately my laptop died so unless I have an issue and can borrow the missus PhD laptop I'm running blind

The above is also why I've not posted a log yet

[Reverant]

Varying injection angle has a big impact on idle smoothness on my V8 (with MS3) so it could easily have a negative impact as you are seeing.

James

Idle quality is GREAT. And as I've said, it does randomly.

[jsmcortina]

Here's an idea to capture this.

Someone get a soundcard scope or similar device that can record "forever" and hook it up to two of the injector channels. (Sound card input can be recorded in Audacity of programme of your choice.)
If it happens, stop the recording, SAVE IT! and remember approximately how long before the end it happened. Send the recording to me for review.

James

[richyvrlimited]

I've not had this missfire occour as yet on the RC1 firmware.

I've only one 30 or so miles mind.

[Reverant]

I upgraded to 3.0.3y the other day and it hasn't happened since as well. I want to test it more to be sure, but so far it looks promising.

[richyvrlimited]

I'm wondering if the code optomisations that Robbs has been dilligently working on has fixed it, like the missfire was due to the CPU runing out of time to do something? I dunno I'm not nearly bright enough to understand.

My idle quality is much improved, it's just smoother somehow I can't put my finger on it, but it is.

[Reverant]

Sam here, re: idle quality. It feels smoother.

[jsmcortina]

There are two recent speedup
- using new assembler divide (~25% improvement in mainloop time)
- Robs tweak (~1% improvement observed in mainloop at high interrupt rate)

The first has no impact on interrupts. The second is a few microseconds perhaps.
I would not _expect_ either to have any impact on what has been reported. Perhaps something else was changed at the same time or perhaps you got lucky?

James