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

[Alvin]

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 !!!

[TriPinTaZ]

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.

[Alvin]

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.

[lt1z350]

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

[TriPinTaZ]

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.

[TriPinTaZ]

Reviving an old thread. I'm monitoring B1S3 on the newer ZL1's and after two logs, the IAT timing multiplier seems to follow closer to this value than to the MAT value.

[GHuggins]

It's my understanding that IAT 1 & 2 are both in the MAF. It appears to use IAT 2 for MAF accuracy or to keep it in line just like a Ford does "I'm assuming here". Then IAT 3 is the actual supercharger air temp and MAT is calculated from that.

[TriPinTaZ]

It's my understanding that IAT 1 & 2 are both in the MAF. It appears to use IAT 2 for MAF accuracy or to keep it in line just like a Ford does "I'm assuming here". Then IAT 3 is the actual supercharger air temp and MAT is calculated from that.

That seems to be the case. I'm wondering if the sensor just after the snout on the LT4's actually has a temp sensor in it as well. Would make sense that would be IAT2 as well if so. Or maybe IAT2 is a calculated value based off of IAT1? It really does appear that IAT3 (b1s3) is the real temp from the sensor in the back of the blower (post bricks) and that the newer ZL1's and 2017+ Z06's actually use this value for the IAT timing pull and not MAT.

As many LT4's as I've worked on, I always forget to actually test or document unplugging or putting a heat gun on the sensors in the blower. When I put the Goliath Pump and XDI's in my personal ZL1 I'm going to remember to test all of the sensors against a heat source so I can verify what is actually affected.

[Alvin]

My understanding is B1S3 is from the Tmap directly. It throws a IAT B1S3 code if you unplug the Tmap.

I could be wrong.

[GHuggins]

That seems to be the case. I'm wondering if the sensor just after the snout on the LT4's actually has a temp sensor in it as well. Would make sense that would be IAT2 as well if so. Or maybe IAT2 is a calculated value based off of IAT1? It really does appear that IAT3 (b1s3) is the real temp from the sensor in the back of the blower (post bricks) and that the newer ZL1's and 2017+ Z06's actually use this value for the IAT timing pull and not MAT.

As many LT4's as I've worked on, I always forget to actually test or document unplugging or putting a heat gun on the sensors in the blower. When I put the Goliath Pump and XDI's in my personal ZL1 I'm going to remember to test all of the sensors against a heat source so I can verify what is actually affected.

I was just going by the schematics. IAT 1 and 2 are both in the MAF and then IAT 3 is the one in the map. The SCIAP doesn't have one according to the schematics. It's just your usual 1.5 bar map sensor.

Then according to how the ecm needs to calculate airflow and density to control the throttle position for torque control it would need to know pressure and temperature before and after the throttle plate, so it would then be using the iat 3 for the post rotor reading going into the cylinders which like you said should be the one also controlling your iat timing adjustments. GM also uses some sort of 3d iat, ect combination lookup controlling table that I don't have a clue on that also plays into all of that.

[TriPinTaZ]

I was just going by the schematics. IAT 1 and 2 are both in the MAF and then IAT 3 is the one in the map. The SCIAP doesn't have one according to the schematics. It's just your usual 1.5 bar map sensor.

Then according to how the ecm needs to calculate airflow and density to control the throttle position for torque control it would need to know pressure and temperature before and after the throttle plate, so it would then be using the iat 3 for the post rotor reading going into the cylinders which like you said should be the one also controlling your iat timing adjustments. GM also uses some sort of 3d iat, ect combination lookup controlling table that I don't have a clue on that also plays into all of that.

Makes sense. Why would they want two IAT sensors in the MAF and why would they read differently? Just curious regarding GM logic.

[GHuggins]

Makes sense. Why would they want two IAT sensors in the MAF and why would they read differently? Just curious regarding GM logic.

I don't know. I just assumed they were being like Ford using a temperature correction scale for the MAF. As to why they read different, I also don't know that. I was just going by the schematics with where everything was located. IAT 2 specifically is reading MAF temp whereas iat 1 is reading intake air temp. I could be completely wrong about it too. It labels iat2 as the hz reading of the maf, so.... It also looks like the maf signal goes to a different pin of the ecm, so not sure exactly?

[lt1z350]

So what I understand is the iat2 is in the tmap and that is why the magnuson kits break that sensor out of it and add that old style lsa sensor in the front of the supercharger. If you unplug the tmap you get no iat2 reading on the log or its -32 defaut. I was told all this directly from mike at too high psi a while back and why they broke that out to get a more accurate reading on the iat3 sensor. My car a 2300 I have port methanol in the short runners of the 2300 so my meth sprays right on that lsa sensor. My iat2 and my iat3 drop over 20 degrees typically vrs climbing when meth starts to spray. it did in the cooler weather anyway yet to test in 95 degree heat lol. I quit using mat a long time ago really as soon as found the b1s3. On my own car since I do see temp drops and not climbing I have considered adding my timing that way for the meth. Still need to test this in the heat but it was nice on some older cars you had the ability to do that as methanol actually saw charge temp drops when you used it in the past. I found the b1s3 quite a while ago so used that vrs mat as everyone knows there is two of them and one doesnt move while one does and its really scary that some tuners still put the one that doesnt move on the channels list so customer sees that and thinks they have a great cooling system and no need to upgrade as it barely goes up on a pull......


Nice to see you on forums again Greg I know took time away I dont make it here much myself as I hate the fact when I try to help some individual that I might be teaching a shop to do things right also so I dont post much anymore just randomly helping. So many shitty tuners taking money from people that dont know any better because they are local or have a big name and its not my job to help them make more money is my perspective on it. I enjoy working with everyone on this thread though and do miss some of that.
Anyway to my findings the b1s3 is the most accurate and even better broken out of the tmap as magnuson is doing it. would be very curious to see this on the lt4 blower to see how much change is seen in temps. Im sure its probably similar to the boost issue where a mechanical gauge will read more boost then a log shows I guess thats something to do with one of the man map sensors and calculations. I did find that on my own car that a mechanical gauge shows about 2 psi more then my logs but I found that when moved to Tennessee and now at 1200 feet so it might be due to elevation and how the ecm calculates all that. Was just trying to trouble shoot low boost after a new blower port that was claimed to add 2 psi and not lose some. I didnt not think from Fl to Tn was gonna be so drastic on boost loss especially running at bristol the et killer race track

[Ben Charles]

B1S3 is what I log for intake temp for blower… if they have a flow issue or air pocket you’ll see this climb to 180-230 degrees and not recover

[JSH]

I've had odd B1S3 the last few days, the highest ever, with the other two at 60F and MAT 99. It can't be right.

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 !!!