Hot start running lean [Fixed]

[Twistedmetal]

Ive run into something interesting, when the car is driving the afrs are spot on, when i shut it down for 10 mins or so an go to restart it it will idle at 17:1 for a few mins and then come back down to 14:1 slowly. Coolent it still at 180 and WE is tuned. No logs or msq until this afternoon. I suspect it it AE not correct yet, just wondering if I am thinking about the right thing.

Input?

[techsalvager]

Check in datalogs if GAIR is moving around.
That effects stuff at restart if it is.
if you fully disable gair and still have it then something externally is effecting fuel as well.

[Twistedmetal]

Check in datalogs if GAIR is moving around.
That effects stuff at restart if it is.
if you fully disable gair and still have it then something externally is effecting fuel as well.

Ill check the logs when i get home, it shouldnt be external, I am not running vac to the FPR so the injectors see 40psi full time.

[S.Bretz]

Are the iat's really hot....err, hotter than after it has been running a few minutes and comes back down? If yes, try to adjust the mat based fuel correction or tweak the aggressiveness of the the pv=nrt calculation and see if that helps.

Personally I would start with the mat base fuel correction table and adjust the fuel up a bit.

[Twistedmetal]

Are the iat's really hot....err, hotter than after it has been running a few minutes and comes back down? If yes, try to adjust the mat based fuel correction or tweak the aggressiveness of the the pv=nrt calculation and see if that helps.

Personally I would start with the mat base fuel correction table and adjust the fuel up a bit.

Honestly I didnt really consider MAT playing a part in hot start, I just checked it and it is completely zeroed out, I dont even know what the right values are. It did it to me at the gas station a few hours ago, I had to throttle it to keep it running until the afrs came down low enough to put it in gear. I still havent figured out why it takes 2-3 cranks to get it to kick over and stay running. Once it is running is is perfectly fine. I would post a log but for some reason everytime I attempt to start a log TS loses the link and locks up the comm port.

I posted my MSQ as of the last pull I did today, I would like to start daily driving my old girl again, but I just cant bring myself to do it with the cold/hot start issue. I would appreciate any pointers, and thank you.

[techsalvager]

zero out values mean it will default to the stock ideal gas law which takes fuel out above 80f~ and adds more below
This is one of the issues with lean restarts. If you change this so its never takes any fuel out above or below and still have a lean hot restart issue, then it is something else, most likely external factor in the engine bay

[Twistedmetal]

zero out values mean it will default to the stock ideal gas law which takes fuel out above 80f~ and adds more below
This is one of the issues with lean restarts. If you change this so its never takes any fuel out above or below and still have a lean hot restart issue, then it is something else, most likely external factor in the engine bay

It must be a heat soak thing then. My IAT is located on the underside of my plenum above the hot motor, it is also in the most direct portion of the air stream. When it is running and even under full boost I never see temps above 110f (big @$$ intercooler). I always thought a zero MAT correction table would disable it. How can I correct the lean hot start without affecting normal operation? I also do not want to move the IAT.

[Peter Florance]

zero out values mean it will default to the stock ideal gas law which takes fuel out above 80f~ and adds more below
This is one of the issues with lean restarts. If you change this so its never takes any fuel out above or below and still have a lean hot restart issue, then it is something else, most likely external factor in the engine bay

It must be a heat soak thing then. My IAT is located on the underside of my plenum above the hot motor, it is also in the most direct portion of the air stream. When it is running and even under full boost I never see temps above 110f (big @$$ intercooler). I always thought a zero MAT correction table would disable it. How can I correct the lean hot start without affecting normal operation? I also do not want to move the IAT.

You may not want to move it but it is probably the best solution. Outlet of intercooler would be ideal.
If car was NA I'd be more comfortable tweeking the air density values.

[techsalvager]

under normal driving in your datalogs what does gair show as?

[Twistedmetal]

under normal driving in your datalogs what does gair show as?

Last time I checked the logs yes, 98-102. It does move, but I am not familiar with the function.

[Peter Florance]

please post log of hot start.

[Twistedmetal]

please post log of hot start.

I will do so on my way home from work this afternoon (4:30cst)

[Twistedmetal]

The included files are half an hour old, 6 mile commute.

[Peter Florance]

The included files are half an hour old, 6 mile commute.

Looks like it's about 9% lean on startup. Check Gair. Should 100% at ~ 77 degrees.



At startup MAT is 129.00

It stays heated up the entire time after the restart. Moving it to intercooler outlet should help if it's not heated by radiator.

[Twistedmetal]

The included files are half an hour old, 6 mile commute.

Looks like it's about 9% lean on startup. Check Gair. Should 100% at ~ 77 degrees.



At startup MAT is 129.00

It stays heated up the entire time after the restart. Moving it to intercooler outlet should help if it's not heated by radiator.

What you say "check Gair", what and where am I looking? I see it in the logs but have no Idea what controls it, how it works or how to change it, honest.

I watch MAT do that too in real time which I found puzzling. I am not trying to be stubborn about the IAT sensor relocation but I am resistant for two reasons, one being that I want the measurement as close to the injectors as possible for dead accurate compensation (no lag), the second being that I in no way want to alter the original harness. I will being building a 100% new harness in the future when I install the wheel, cam sensor and COPs for full sequential timing and fuel.

I will be happy if it doesn't shoot past 15:1 on hot start,If there is hot air there I want it to correct for it, but if it is a false reading from heat soak then will have no choice but to move it. What I dont understand is why the sensor isnt picking up the cooler air on restart, it is directly in the most turbulent part of the air stream, it also instantly detects any other MAT changes.

[Peter Florance]

The included files are half an hour old, 6 mile commute.

Looks like it's about 9% lean on startup. Check Gair. Should 100% at ~ 77 degrees.



At startup MAT is 129.00

It stays heated up the entire time after the restart. Moving it to intercooler outlet should help if it's not heated by radiator.

What you say "check Gair", what and where am I looking? I see it in the logs but have no Idea what controls it, how it works or how to change it, honest.

I watch MAT do that too in real time which I found puzzling. I am not trying to be stubborn about the IAT sensor relocation but I am resistant for two reasons, one being that I want the measurement as close to the injectors as possible for dead accurate compensation (no lag), the second being that I in no way want to alter the original harness. I will being building a 100% new harness in the future when I install the wheel, cam sensor and COPs for full sequential timing and fuel.

I will be happy if it doesn't shoot past 15:1 on hot start,If there is hot air there I want it to correct for it, but if it is a false reading from heat soak then will have no choice but to move it. What I dont understand is why the sensor isnt picking up the cooler air on restart, it is directly in the most turbulent part of the air stream, it also instantly detects any other MAT changes.

GAIR is air density compensation. It is a variable in your datalog. It is part of the fueling calculation that the MS2Extra code uses to figure out how much fuel your engine needs.
The commanded fuel is multiplied by that %. In your case the commanded fuel is leaned out by 10% because the MS thinks the air is that hot.
Horribly inaccurate but timely MAT readings are much less valuable than slightly later (probably 100msec) MAT values that are correct. If you don't move it or engineer some effective insulating system (non metallic bung, heat shields etc) be prepared to live with it.

Of course if you get into boost before the sensor cools down, you could be leaning out your boosted mixtures.

[Twistedmetal]

Thank you for that explanation, it is greatly helpful. So basically this can be simply fixed by relocating the IAT. I wondered why VEAL keeps screwing with my VE tables, the false reading has been changing boost mixtures depending on the vehicle run time, idling in traffic has also been screwing with mixures and I have chasing my tail.

The IAT is moving now, thank you.

[Peter Florance]

Thank you for that explanation, it is greatly helpful. So basically this can be simply fixed by relocating the IAT. I wondered why VEAL keeps screwing with my VE tables, the false reading has been changing boost mixtures depending on the vehicle run time, idling in traffic has also been screwing with mixures and I have chasing my tail.

The IAT is moving now, thank you.

It will be nice to get another datapoint showing that the math does work if the data is good.

Really we need an sticky about heatsoak and false readings of MAT. It is a huge problem.

[techsalvager]

I still have lean hot restarts despite having a gair stuck at 100%
so I know there is something external to the ecu effecting fueling.

[Twistedmetal]

I want to thank everyone for their patience and help, I have been fighting this for weeks now. For the first time I was able to cold start my old girl in one crank, not 4. Hot start is no longer and issue and with the low variance in temperature lag will not be an issue. I fired it up and she roared like like an angry beast, no more idle miss and AFRs are rock solid stable, I was starting to think that the AFR dancing around was normal. MAT reads dead ambient with no variation (68F up here in Northern Minnesota right now) and hot start is the same. I dont know why an OEM would put a IAT sensor up on the plenum at all. Thank you, thank you, thank you! Please sticky this thread!


Pics of relocation