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Old 04-18-2010, 06:45 PM   #1
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Default IAT correction follow-up

A few months ago (October last) I started adjusting my IAT correction settings but before I got very far the engine was pulled (unrelated issue). It's five months later, new block, head, Wiseco pistons/rings, Carrillo rods... and I am back to tuning (mostly treading until the break-in phase is finished and I can take it for dyno tuning).

On the IAT Correction: My AFR stability over temp has always been poor and I finally resorted to using the EGO correction at idle. I would love to optimize this and I suspect my IAT settings need adjustment. Right now I run the MSPNP defaults:
temp - IAT correction
50 - 105
55 - 110
60 - 115
65 - 119
70 - 124
75 - 129
102 - 155

I have a few options and if anyone has insight I would love to hear your take (in case the specific configuration helps - It's a turbo 91, MSPNP(rev C w/ Mapdaddy 400kpa sensor), no afm, GM IAT mounted at the intake manifold inlet, LC1 O2, 550 RC eng injectors):

Option 1) Switch to Normal Correction (same as setting all the Corrections to 100?)

Option 2) set my corrections at 100(no correction) and use the higher temp bins for warm start IAT heat soak management (if you think this is optimal, what temperature bins/corrections would you use?).

Option 3) Use the IAT corrections and tune for all temps (if so, what bins/temps would you recommend as the starting point, what start/stop rpm thresholds would you set?)

Option 4) Anything I have not thought of?

Any thoughts or links would be great (I have been reading much discussion of this over years of posts if anyone has a definitive post to point me to, feel free).

Last edited by aseer; 04-18-2010 at 07:13 PM.
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Old 04-18-2010, 07:12 PM   #2
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It looks like you're having similar issues as me... My problem was that i'd tune the car at 50*F and it would be nice & steady... THen the season would change and we'd be seeing 70*F or 80*F ... Invariably, the car would run lean. Re-tuning at this temperature would be OK for a while, but too lean when temps hit near 100... Then repeat the same in reverse when temps cooled down for winter time.

I've been wrestling with this problem for a while...

I'm not an MS genius but i think there's something wrong w/the way my MS was interpreting temperatures..

My 'check' for this is as follows: Go into your iat correction table, and change the corretion % to 150 for 1 degree higher and 1 degree lower than the IAT currently displayed in megatune. IN other words, if megatune says IAT is 60*F,

do

0 - 100
58 - 100
59 - 150
61 - 150
62 - 100
100 -100

The idea is to create a big spike right at the 'current' temperature... FOr *ME* it never would... i would have to make the spike off by 10 or 20*F for it to register. THis told me that megasquirt thought it was actually a different temp then megatune did.

let me know what happens for you!

My config is a braineack-built MS, gm-iat, no afm, turbo, 305CC w/rrfpr, intercooler, iat sensor on IC piping right before tb.

-tomaj
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Old 04-18-2010, 07:33 PM   #3
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I am a step behind you I think and am just trying to figure what my starting point should be for IAT correction management (which I am pretty sure should be changed from the MSPNP defaults, at least I think so). If the MSPNP is not interpreting the IAT properly then I have other more serious issues (Megatune reads it perfectly, I have checked that with a calibrated TC).

So I guess I should add the disclaimer, which of the options I listed would you choose from the above assuming the IAT is being properly read by the MSPNP?
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Old 04-18-2010, 08:57 PM   #4
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i may be wrong here but i think that you shouldn't ever really NEED the IAT correction table provided everything is in order. (some here may disagree)

All that table does (and i may be wrong once again) is adjust fuel based on temperature. X temp, Y adjustment... the question i always have is -- why do you need to adjust fuel based on temp? Shouldn't the airdenfactor be doing that?

Some people say it is to combat heatsoak of the IAT sensor. To me that doesn't really make sense -- because the IAT (if properly placed) will only get heatsoaked if you're standing still and/or if you shut off the car and then turn it back on again a few minutes later. I think that using after-start-enrichment would be a better way to ward off those few seconds of iat-caused false leanness rather than altering your iat correction table.

The reason being that lets say it's really 80 degrees outside, but your iat sensor reads 100 degrees because you let your car sit for 10 minutes while you went to the bank... now when you get back in, your car will be artificially lean for a few seconds while your sensor cools down due to the fresh air going by it. BUT if you were to adjust your iat correction table to compensate at 100* by adding 10% fuel lets say, then when it really IS 100*F outside, then you'll end up being 10% too rich... right?

** all of the above may be refuted by someone who actually knows what they're talking about **
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Old 04-18-2010, 11:32 PM   #5
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im gonna just subscribe to this thread, i hate my heat soak issue, im getting about the same problems as you guys..... i need some more info on how to get rid of this .....
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Old 04-19-2010, 10:26 AM   #6
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my table in MS-II, with my AIT sensor just after the IC is, IIRC:

40.5 -3.0%
42.5 -2.0%
50.0 -1.0%
60.0 0%
100 2.0%
150 5.0%

The best thing you can ever do is keep the AIT outside of the engine bay.
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Old 04-19-2010, 11:32 AM   #7
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Quote:
Originally Posted by Braineack View Post
The best thing you can ever do is keep the AIT outside of the engine bay.
Cold side intercooler tank is win.
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Old 04-22-2010, 02:06 AM   #8
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At some point I'll think about moving the IAT sensor if I need to (right now it is where DIYAutotune suggested I stick it, at the TB inlet). Moving it in the short term will cause other problems.

I think I'll try Option 1) for a bit and go to Normal Correction. Can anyone suggest a graceful way to transition from my current IAT correction to Normal? (It is a pretty aggressive correction so pulling it out will screw up the tune big time - I would be nervous about just running VE Analyzer on it and remapping)
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Old 04-25-2010, 03:20 PM   #9
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Where exactly can these settings be found in Megatune or Tunerstudio? My car does the same thing always changing the tune with changing temps, it hasn't been to far off yet fortunately.
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Old 04-25-2010, 04:25 PM   #10
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coolant related air-density correction table.
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Old 05-07-2010, 02:40 PM   #11
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Red face wrong sensor?

Quote:
Originally Posted by Braineack View Post
coolant related air-density correction table.
Hi

In my air-density correction table it looks like the CLT sensor is active instead of the IAT sensor. How can I fix this problem?

regards: citat
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Old 05-07-2010, 02:42 PM   #12
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go to advanced settings and change it from CLT to AIT.
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Old 05-07-2010, 03:09 PM   #13
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Quote:
Originally Posted by Braineack View Post
go to advanced settings and change it from CLT to AIT.
The settings in the advanced settings is on IAT corrected, but the table still use CLT sensorn for density correction.

Regards: cittat
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Old 05-07-2010, 03:18 PM   #14
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it shouldn't. are you using MegaTune? the gauge will always display the CLT temps.
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Old 05-07-2010, 03:34 PM   #15
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Quote:
Originally Posted by Braineack View Post
it shouldn't. are you using MegaTune? the gauge will always display the CLT temps.
I use TS and I have tested MT on this isue but no different.

citat
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Old 05-07-2010, 04:38 PM   #16
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Quote:
Originally Posted by citat View Post
The settings in the advanced settings is on IAT corrected, but the table still use CLT sensorn for density correction.

Regards: cittat
The live graph will still show you CLT, but if you changed the setting, the MegaSquirt will actually be using IAT.
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Old 05-07-2010, 04:57 PM   #17
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I don't understand why one would want to have steadily more fuel as air temps go up .. ?
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Old 05-07-2010, 05:01 PM   #18
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we use that to battle heat soak on warm starts. else it reports false high temps and the system leans out.
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Old 05-07-2010, 05:57 PM   #19
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The MAT correction on most MS firmware is overly aggressive. It leans out too much at temps over 70F and richens too much at temps below 70F.

The "correction" curves in the MS correct the original curves. So since the original curves lean things out too much at higher temps for most engines, you must increase the amount of fuel a little bit at higher temperatures.

Ken
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Old 05-09-2010, 12:18 AM   #20
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Quote:
Originally Posted by muythaibxr View Post
The MAT correction on most MS firmware is overly aggressive. It leans out too much at temps over 70F and richens too much at temps below 70F.

The "correction" curves in the MS correct the original curves. So since the original curves lean things out too much at higher temps for most engines, you must increase the amount of fuel a little bit at higher temperatures.

Ken
I had the same hypothesis as you... so i found the formula for the density of air online and spot checked a few of the points on the airdenfactor file. From what i saw, their calculations were spot-on. For example (numbers not real), if at 50*F air is 115% as dense as at 68*F, the corresponding fuel multiplier was 15%..

I personally wish that the MS would output the gamma air-density, that would make things a bit easier to diagnose.
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