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Thread: LT4 guys... Notice Intake Air Temp B1S3 yet???

  1. #1
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    LT4 guys... Notice Intake Air Temp B1S3 yet???

    Just curious...

    I'm trying to diagnose a intercooler issue on a LT4 CTSV and have been used to looking at IAT 1, 2, and manifold air temp for GEN 5's. The manifold air temp being the one I assumed was like a LSA IAT2 equivalent but calculated instead of actual. Post blower, post intercooler charge temp. This never really sat well with me though because the IAT spark adders and multipliers do not match up with this value.

    Today I happened to notice Intake Air Temp B1S1..... to B2S3 (6 total). It looks like B1S3 is post blower/cooler IAT. To try to prove this I unplugged the sensor while scanning and observed no change but did get a IAT B1S3 code.


    Anyone else try to log this yet? I'd like to know what is normal. I'd like to see this logged on a bone stock LT4 to see what is appropriate. Manifold air temp was always crazy high compared to what we were seeing on older builds like LSA, magnacharger, etc. I'd assume a normal raw IAT3 for a LT4 would be the same as a LSA IAT2... 100f to maybe 130f normal driving. Would love to know for sure!


    Anyone willing to log IAT B1S3 IAT, IAT2 and manifold air temp? would be appreciated !!!
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  2. #2
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    There has been no real clear agreement on what is what with the LT4. The most sense I have been able to make is that the Base IAT table references MAT PID but the multiplier references actual IAT #2 PID. No other math makes sense whatsoever and I'm not even sure that is right.

    I was datalogging a WOT run the other day and the MAT was 160 degrees. Based on stock tables using MAT for both the base and multiplier, that would be 2.1-2.5 degrees at least of IAT timing pulled. But the car pulled a max of 1.3 degrees. Only MAT as base and IAT2 as multiplier made sense.


    Anyhow, I haven't noticed any new PID's for temps. I'll do an interface re-scan and see if any new PIDs pop up later today or tomorrow.
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  3. #3
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    Quote Originally Posted by TriPinTaZ View Post
    There has been no real clear agreement on what is what with the LT4. The most sense I have been able to make is that the Base IAT table references MAT PID but the multiplier references actual IAT #2 PID. No other math makes sense whatsoever and I'm not even sure that is right.

    I was datalogging a WOT run the other day and the MAT was 160 degrees. Based on stock tables using MAT for both the base and multiplier, that would be 2.1-2.5 degrees at least of IAT timing pulled. But the car pulled a max of 1.3 degrees. Only MAT as base and IAT2 as multiplier made sense.


    Anyhow, I haven't noticed any new PID's for temps. I'll do an interface re-scan and see if any new PIDs pop up later today or tomorrow.

    I agree with all that you said until I found those pids today by chance. Tell me what IAT S3B1 says. It matches up exactly with the IAT spark adder * multipliers on the file I'm working on.. Well maybe off by .4 degrees but that coudl be interpolation error. I'm excited to finally have a true post blower/cooler IAT reading on these things.

    IMHO the intercooler pump/tank/ lack of res on most LT4 platforms is just shamefully underdesigned.
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  4. #4
    Advanced Tuner lt1z350's Avatar
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    I have found the only way to get true manifold temp is to log both that say manifold temp. If you log only one you get the one that isnt reacting to much of anything. If you log both the second one down will react a lot more to what looks to be normal and it is the one that when you unplug the sensor on the back of the blower it will drop so that is taking the reading from there. On my current setup I am seeing it drop to ambient when on the highway at speed or if really hot out like now it will fall to intake air temp read from the maf. I have done a few upgrades including my pump recently and it has really paid off on cooling this small blower with the 9.55/2.30 combo I am currently running on it. I will also look into this pid as going to be doing some more vve tuning shortly now that I got this cool
    First 9 second 6th gen lt4 zl1 stock blower SHC SBE boost only.

    2013 cadillac ats 2.0t Big turbo-gone
    2007 tahoe 5.3 lsa blower on 14 lbs boost 6l80e swap 2009 os
    2017 zl1 a10 big gulp/2 inch headers/ 9.55 lower/ e85/bigger hx /103mm tb / Synergy trunk tank and underhood kit/methanol injection with torqbyte controller and prometh pump / Jokerz performance R&D ported stock blower/ lme cnc heads /GP tuning custom cam. So far 9.30@150

  5. #5
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    If anyone is reading this I'd like to provide an update on what is what. What I have found is 2015-2016 LT4's use Manifold Absolute Temp as the reference point for both the IAT reference and the Multiplier reference. 2017+ LT4's use the Manifold Absolute Temp for the IAT reference table and the actual IAT1 temp for the multiplier table.

    This is the only way I could match them up to make sense. I was tuning a 2016 Z06 and a 2017 Z06 on the same day and was able to verify this. The 2017 DEFINITELY did NOT use MAT for both tables from what I saw.
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