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Old 08-17-2008, 11:50 AM   #1
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Default Coolant Corrected Air Density & Hot IAT Idle

So I've been getting this intake temperature related lean condition when my car heat soaks in stop and go traffic. At normal intake temps (80-100F), the car idles well at ~14.0AFR. Once in stop and go, the intake temps rise to 110-120F and the car idles at ~15-16AFR.

I was able to fix this issue by changing the Coolant Corrected Air Density. Go to Megatune -> Advanced -> Coolant-Related Air Density (2nd from bottom). The chart only goes up to an intake temp of 102F, which did not go high enough. I took the temp-correction chart and piped it into Excel, fit a 2nd order polynomial , and extracted to 120F. At this point, I need to enter 173% as the Offset % value, but Megatune won't let me enter values that high in the GUI.

To change it, I opened the MSQ in Notepad and edited it there. Once open, search for a block like this:

<constant name="IATCTemp" rows="7" units="F">
50
55
60
65
70
75
102
</constant>
<constant name="IATCor">&quot;Corrected&quot;</constant>
<constant name="IATCorS" rows="7" units="%">
105
110
115
119
124
129
155
</constant>


and replace with:

<constant name="IATCTemp" rows="7" units="F">
50
60
70
80
90
100
115
</constant>
<constant name="IATCor">"Corrected"</constant>
<constant name="IATCorS" rows="7" units="%">
105
115
124
134
143
153
167
</constant>


Now, my car idles at a consistent AFR whether the intake temps are 80F or 120F.
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Old 08-17-2008, 11:53 AM   #2
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thats a huge differential. when i was using it i only had to enter a value of like 115 at 120F.

I didn't like that as a fix so I moved my IAT sensor out from behind the radiator and now my IAT at idle doesn't move when I come to a stop most of the time. If i sit for 15 mins it'll rise 3-5 degrees.
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Old 08-17-2008, 12:10 PM   #3
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Paul,

I should mention that the values in red are what come with the base map in MSPNP. My motor is also bone stock, so the AFM sees plenty of heat from radiator and header (even though I have the stock heat shield on), especially on hot days.
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Old 08-17-2008, 12:15 PM   #4
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really? mine weren't set like that on my 94MSPNP. I am sure that if I could get my car to heat soak to that temperature again and I threw 167% of the ve value at it it would stall quicker than girls turn down ArtieParty and call the police.
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Old 08-17-2008, 12:47 PM   #5
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I really need to move my sensor...just yesterday I was able to jump the temps to 120*F...simply sat in the sun after driving, car off, had the fan blowing on it. Where did you move yours to?

What I'm confused about is why zzxy couldn't simply type in new temperature & correction values inside MT and be done with it?? Hell the Curve Editor will do the work for you.
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Old 08-17-2008, 12:55 PM   #6
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Paul - my car is a 1990, which might explain the difference.

Braineack - I tried entering a higher value in the correction% area, but MegaTune threw me an error saying the highest correction value I could manually enter was 150% in the GUI. I never tried curve generator, but, heck, if that works for higher values, it sure sounds a lot easier than going into the Wordpad to edit the MSQ.
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Old 08-17-2008, 01:00 PM   #7
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i dont see why you'd need more than 150% correction...**** must get HOT. But then agin you are only correcting to 115*F...so very curious.
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Old 08-17-2008, 01:16 PM   #8
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Highest intake temps I've ever seen was 132F in heavy stop and go in 95F 90% humidity. It was terrible, and I idled at ~16-16.5 afr with lots of lean pops.

The current correction does run a bit rich around 13.5 when it gets really hot, but the idle quality is pretty good at high temps, so I'm satisfied with it.
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Old 08-17-2008, 01:32 PM   #9
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Did you bother even seeing what it might idle at with corrections keeping it closer to 15.0:1? I would not be happy with a 13.5:1 AFR idle.

If it were me, I'd start corrections closer to 90*F. And fine tune it while sitting at idle to keep the AFR consistent.

something like this:

85 100
95 115
100 120
105 125
110 130
120 135
130 140


I dont see any reason to have corrections active doing non-heatsoaked conditions.
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Old 08-18-2008, 12:36 AM   #10
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Scott. moved my IAT sensor to the outlet pipe after the IC. So it's no longer behind the radiator. Shitty cell phone pic coming...
Attached Thumbnails
Coolant Corrected Air Density &amp; Hot IAT Idle-iat_relocated.jpg  

Last edited by paul; 08-18-2008 at 12:43 AM. Reason: added pic
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Old 08-20-2008, 12:22 AM   #11
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Hmm... Yeah, I'll have to play with the values some more. For some reason, when I idle leaner than mid 14's I get a some pops out of the exhaust and motor just doesn't seem quite as smooth. Heck, maybe it's just me.

Paul, any luck with the new IAT sensor location?
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Old 08-20-2008, 12:37 AM   #12
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Quote:
Originally Posted by zzyx7 View Post

Paul, any luck with the new IAT sensor location?
Quote:
Originally Posted by paul View Post

I didn't like that as a fix so I moved my IAT sensor out from behind the radiator and now my IAT at idle doesn't move when I come to a stop most of the time. If i sit for 15 mins it'll rise 3-5 degrees.
.
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Old 08-21-2008, 09:16 PM   #13
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OK, so I got sick of playing with these values and turned the correction off completely. Pretty interesting... Idle got nice 'n steady temp-wise, from cold start to heat soaked. Got up to 125F in traffic today, and it was still steady at ~14.5 AFR.

My guess is the base map from DIY relies rather heavily on coolant correction to get good idle AFR's, but created a good deal of temp based variation.

Base Map w/ base coolant correction values vs. New map below:
Attached Thumbnails
Coolant Corrected Air Density &amp; Hot IAT Idle-mspnp-base-map.jpg   Coolant Corrected Air Density &amp; Hot IAT Idle-newmap.jpg  
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Old 09-28-2008, 10:03 PM   #14
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Quote:
Originally Posted by paul View Post
moved my IAT sensor to the outlet pipe after the IC. So it's no longer behind the radiator.
Paul did the same trick on my MSM this morning. Seems to help a lot with the idle.
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Old 01-01-2009, 07:14 PM   #15
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I know this is a bit old... but here is an alternative to manually editing your msq. You can change the max value in megatune by editing msns-extra.ini:

Find the following lines:
Quote:
; Coolant related correction table for air density
IATCorS = array , U08, 47, [7], "%", 1.0, 0.0, 50, 150, 0
And change the max value (150) to something higher:
Quote:
; Coolant related correction table for air density
IATCorS = array , U08, 47, [7], "%", 1.0, 0.0, 50, 200, 0
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