MAT correction issue - leaning out on hot starts - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 06-16-2014, 05:19 PM   #21
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Quote:
Originally Posted by Braineack View Post
does the purge solenoid allow the gas tank to vent on a returnless?
Stock has a relief in the back off the canister that relieves pressure, but I'm not sure at what pressure. My line at engine is plugged, so I am relying on that same relief to control tank pressure. Purge valve has gone missing.
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Old 06-16-2014, 05:49 PM   #22
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Looks like this thread has turned from MAT correction lean to Returnless Lean. So, I'm back in.

I am also, and still, under the impression that I have restart lean due to high fuel or injector temperature. I have attached logs of:
1) Idle after having run
2) A restart in about 1 minute of shutting down
3) A restart after about 30 minutes

Synopsis:

Restart After
Variable Idle 1 min 30 min
MAP 30.9 28.7 26.7
RPM 895 898 900
EGO 90 94.1 110
AFR 15.0 14.9 16.6
PULSE 1.756 1.742 1.886
CLT 198 197 178
MAT 87.2 89.5 87.7

As you can see, a 20% swing in EGO is not enough to control the AFR
Yellow 425cc injectors with dead time set at 0.8mS.

Note: I have large ASE and ASE time at above 130 CLT to allow a rich enough mixture until the EGO takes over on a restart. Kind of works, but not fixing root cause.

End of synopsis. Start of thoughts, assuming that evaluation of the information I have uploaded does not lead someone a cause I am over-looking.

If indeed the issue is injector heat soak causing long dead times, then I see (3) benefits to going to a return system:
1) Removal of damper and loops means less volume of hot fuel to burn before issue goes away at each restart.
2) Manifold reference of regulator means that the idle pulse widths are longer and the dead time variance makes less difference.
3) Fuel pump priming and running pushes some of the hot fuel through the rail and back to the tank.

DNM
Attached Files
File Type: msl stop_and_idle.msl (222.2 KB, 72 views)
File Type: msl immediate_re-start.msl (333.2 KB, 64 views)
File Type: msl 30_min_restart.msl (346.1 KB, 21 views)
File Type: msq DNM_Tune.msq (192.4 KB, 53 views)

Last edited by DNMakinson; 06-16-2014 at 05:53 PM. Reason: Trying to get the table to behave
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Old 06-20-2014, 06:27 PM   #23
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Braineack, JasonC, anyone see anything in my logs or MSQ that shows something I am missing that can be fixed with tune?
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Old 06-21-2014, 02:13 AM   #24
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I have posted this before.

After a hot restart the injectors are much warmer due to heat soak and no fuel flowing in them. This increases their dead time because their resistance increases and the current rises more slowly at the start of the pulse. Much more significant with big high impedance injectors.

If dead time is 1.0 ms, and at idle the car needs 0.2 ms of fuel, then the electrical pulse is 1.2 ms. If the dead time increases to 1.05 ms, then 0.15 ms of fuel is delivered. That's 25% less fuel.

I suspect that the AIT correction complaints claiming that the ideal gas law is wrong, are probably based on observations at light load where the injector pulses are short, not at full load.
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Old 06-21-2014, 06:41 AM   #25
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With ms3 there is a dead time curve you can tune, but it's 2D based on voltage. How would you tune out that behaviour Jason?
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Old 06-21-2014, 11:40 AM   #26
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Quote:
Originally Posted by DNMakinson View Post
Synopsis:

Restart After
Variable Idle 1 min 30 min
MAP 30.9 28.7 26.7
RPM 895 898 900
EGO 90 94.1 110
AFR 15.0 14.9 16.6
PULSE 1.756 1.742 1.886
CLT 198 197 178
MAT 87.2 89.5 87.7

your EGO at idle suggests your fuel map is poorly tuned. Youre leaning it out 10% at idle, but then adding 10% when it's lean.

add 10% to your VE table at idle. then at 110% EGO, that's 20% more fuel.

so try changing your idle cells from 56% VE to 61% and see what effect that has. then at 110% EGO, you'll be at 67%VE instead of 61...



oh wait... no. ****.

Last edited by Braineack; 06-21-2014 at 11:55 AM.
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Old 06-21-2014, 11:57 AM   #27
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Quote:
Originally Posted by JasonC SBB View Post
I suspect that the AIT correction complaints claiming that the ideal gas law is wrong, are probably based on observations at light load where the injector pulses are short, not at full load.

possibly, they change the code because of us from the original implementation, but never did add back in the RPM filter like we wanted to decay the correction back to ideal at higher rpms...
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Old 06-21-2014, 03:36 PM   #28
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Great info in this thread!

Those of you with returnless fuel systems, I would not expect changing to a return type fuel setup to magically clear up all of your lean on hot restart issues.

I have a NB2 VVT engine, but am running the NA "return type" system with NA pressure regulator and return line to tank. During an "open" track day (drifting) with the return type fuel system, my Miata was going lean on hot restarts until driven around the pit area. Idling in place eventually corrected the problem, but it took quite a while. I am taking 5+ minutes to clear up during the heat of the day. I also had a lot of pressure build up in the gas tank, so I believe that the fuel temp in the tank had risen to the point that it wasn't helping cool the injectors much at all.

When I was having this lean on restart problem, I compared map and injector pw at different AFR's with the engine idling (~950rpm). The map and pw were very close, yet AFR was extremely lean (17+). This supports the theory/claim that there is a mechanical/fuel problem related to heat soak. The increase in injector deadtimes makes sense. However, I also wonder if the very hot gas had become aerated, further reducing the density beyond the reduction from the temp increase. It could even be a combination of the two...

This has to be a larger problem than just Miatas with Megasquirt ECUs.... Do AEM, Motec, etc ECU's have an injector deadtime compensation curve based on CLT and maybe other factors like run time? How about the Miata OEM ECU's?
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Old 06-21-2014, 04:29 PM   #29
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I have posted this before.
Yes, but thanks for responding here. As I recall, you were working with Reverant on a possible solution to the issue. Any progress?

I think I am doing about the best I can with my situation, and it appears that scot was going to recommend exactly that solution.

My questions:
1) Is there a better, preferably tuning, solution?
2) Any other comments on potential improvement by going to a return, referenced regulator system? NoName suggests not. Are there any other data points from guys who have run the same car both ways?
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Old 06-21-2014, 09:17 PM   #30
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I have a circuit idea to drive hi-impedance injectors similarly to lo-impedance injectors to reduce the problem. Seems a bit overkill. No progress.

Other possible solutions include:
1) A deadtime correction curve vs. CLT or intake manifold temperature (lol). Some OEs I think, do have intake manifold temperature sensors.

2) Have a feedback loop recognize that the dead-time is wrong by seeing the behavior of the AFR and correct it with a dead-time offset variable. Or simply bump the dead time when the short term fuel trim hits -15%.

3) Have a model of heatsoak and do the same as (2)

4) have a circuit measure the current waveform and determine the temperature of the injectors and adjust the dead time accordingly.

All of the above seem complicated but...

I have an uninstalled Adaptronic e1280s with its infinite programmability. I can implement either #1 or #2.
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Old 06-22-2014, 11:00 AM   #31
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Quote:
Originally Posted by Braineack View Post
i will explain:

the ideal gas law code of the MS is aggressive at best.

If you're reporting intake temps higher than 80F, real or not, the MS is going to pull a lot of fuel and the only way to counter the effect is to tune out the ideal gas law algorithm by using the MAT corrections table to zero them out and then fine tune them yourself.
My setup is currently naturally aspirated and running on E-85.

I was totally lost on this until I asked Reverent what the hell was going on. I would tune on a cool evening (65F ambient) and get the tune damn near perfect A/F ratios (15.5 at cruise at anywhere from 2000 to 5000 RPM, 13:1 at WOT) and the next day in the heat (85F ambient) I would be running 16.5:1 at cruise and 14:1 at WOT! So I would think I messed up my tune, redo it until it was once again correct... and then at night in the cool evening air I was running 14:1 at cruise and 11:1 WOT! It was driving me nuts until I asked Rev what was going on. Now I am in the process or correcting my IAT table.

I was planning on having my AIT post intercooler after installing my turbo system (Step promises next week ) but I was wondering if we would be better off with it in the intake track near the air filter? Any reading over 150F isn't going to have any correct "at cruise" tuning to have a AIT correction applied to it... we will always be WOT to get those temperatures post intercooler. With the AIT in the pre-turbo intake track your tune would look very different than someone with the AIT post intercooler... but which one would be better for drivability, hot starts, changes in weather etc.?

Just some more salt to add to the wound of dealing with the MS3 air temperature compensation

Keith
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Old 06-22-2014, 11:13 AM   #32
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I was planning on having my AIT post intercooler after installing my turbo system (Step promises next week ) but I was wondering if we would be better off with it in the intake track near the air filter? Any reading over 150F isn't going to have any correct "at cruise" tuning to have a AIT correction applied to it... we will always be WOT to get those temperatures post intercooler. With the AIT in the pre-turbo intake track your tune would look very different than someone with the AIT post intercooler... but which one would be better for drivability, hot starts, changes in weather etc.?
no. think about it...
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Old 06-22-2014, 11:22 AM   #33
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Quote:
Originally Posted by JasonC SBB View Post
I have a circuit idea to drive hi-impedance injectors similarly to lo-impedance injectors to reduce the problem. Seems a bit overkill. No progress.

Other possible solutions include:
1) A deadtime correction curve vs. CLT or intake manifold temperature (lol). Some OEs I think, do have intake manifold temperature sensors.
Would a coolant temperature sensor surface mounted to the metal of the fuel rail be a good measure of heat soak for the fuel injectors? If so, would the MS3 have any way of using this information to affect injector dead times or would we need a new version of the code?

Keith
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Old 06-22-2014, 11:37 AM   #34
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Originally Posted by Braineack View Post
no. think about it...
I get dangerous when I start thinking

What I am getting at is that any AIT correction we have above 120F or so is just numbers pulled out of our ***, and then we do the actual tuning based on what our A/F ratio is in the real world. So, I can have the AIT sensor down stream of the intercooler and have compensation based on numbers in the AIT correction table that I pulled out of my ***.... or have an AIT correction table that is correct at the intake pre-turbo and have my tune based on that. I know that under boost the curve is very non-linear, where raising pre-turbo intake temp by 10F will raise manifold temperature by 15F or more... but as long as it is consistent you will still end up with a good tune. My question was will this make any difference in daily driving / weather compensation.

In summery, already did the dangerous part (thinking) and I don't see how it would make much difference in daily driving / weather change compensation but I was wondering if there was something I missed

Keith

PS: I am a data junkie, I have the canbus 20 channel data box from Reverent that I will be using for temperature at the air filter, pre-intercooler, and post intercooler. If I go to an air to water system (drag racing with ice tank, NOT road courses) I will add ice tank temperature, pre and post IC core, and pre / post intercooler radiator core temperatures to my logging. I may add a coolant temp sensor surface mounted to my fuel rail just for giggles.
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Old 06-22-2014, 11:50 AM   #35
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well this is why i wanted a MAP or RPM filter to remove AIT corrections, but no one listened to me.

I like to zero out the AIT corrections, then fine tune them based on real life data to keep AFR where they should be based on real conditions; never had an issue after that.

Last edited by Braineack; 06-22-2014 at 12:06 PM.
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Old 06-22-2014, 12:26 PM   #36
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well this is why i wanted a MAP or RPM filter to remove AIT corrections, but no one listened to me.

I like to zero out the AIT corrections, then fine tune them based on real life data to keep AFR where they should be based on real conditions; never had an issue after that.
But the corrections will be wrong in a newly warmed up motor vs. a heatsoaked newly started one.

I can see the approximate deadtime when I put a current probe on the injectors. Indeed it lengthens when heatsoaked. And increasing the deadtime made it idle and act properly. Changing the VE or AIT corrections was a kludge.
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Old 06-22-2014, 12:54 PM   #37
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There is actually a 2nd, smaller effect that screws up fuel calcs at hot idle, and this is what what Braineack's suggested fixes attempt to address (and which Reverant AFAIK already does).

The AIT sensor does not track the actual air temperature at the valves at low airflows. This is because the air will heat up somewhat as it flows past the hot intake manifold runners.

One other ECU solves this by "blending" the CLT temperature with the IAT temperature as a function of RPM (which really should be a function of airflow which is RPM * VE). i.e. at say 5% power (or 1000 RPM if RPM is the X axis), realIAT = 80% CLT + 20% IAT.
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Old 06-22-2014, 01:57 PM   #38
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Ms has this function iirc, but its not documented.
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Old 06-22-2014, 05:57 PM   #39
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Ms has this function iirc, but its not documented.
Quelle surprise
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Old 06-22-2014, 07:08 PM   #40
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Quelle surprise
It's the %CLT used in MAT vs. Airflow table.

Where airflow = load*rpm
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