Air Temp sensor Relocation Questions
- Thread starter vader87
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You should mount it in the intake tube. But, if you extend it and mount it behind the headlight where it can get a cool fresh breeze, it will dramatically reduce the timing retard that happens from heat soak. Some timing retard is triggered directly from detonation, and some happens as a result of the air temp sensor readings. Its a liability thing thats put into the code of practically every EFI car out there. You can thank the warranty companies for bringing that around...as well as shift retard, tip-in retard, etc. They figure the car is more likely to detonate in high temps, as well as high coolant temps, so they pull the timing when it gets too hot. I actually used a different thermistor (thats what the actual element in the sensor is called). I used one that reads about 30 degrees colder than ambient and stuck it in the plug. Now when my car heats up, it doesnt feel like its lost a bunch of power. On my old car, I spliced a resistor inline with the sensor to make the computer think the incoming air was cooler cause I didnt have another thermistor. A thermistor is a resistor that changes resistance depending on temperature. All the retard that comes from heat soak vanished. In many cases, making the computer think the air is colder can increase timing advance by a few degrees....not just eliminate retard.
VadersV6 said:
Got a link to where the IAT timing table is used in the TR's.
From my reading of the code, the IAT bias, and IAT timing tables are 0'd out.
While the later PCMs use a torque management that use a shift timing correction, I've not seen that in the TR code, same with the tip-in retard.
If you can show me where those items are in the TR it would be appreciated.
The only effect the IAT has, is for fueling. In the N/A applications, the IAT timing stuff is used.
Yup, thats where its supposed to be. If you have cold air induction like that guy, your heat soak timing retard will practically be eliminated. Ive always believed that a good portion of the track gains from a cold air setup can be attributed to keeping the sensor from spitting out high temp readings. Ive tried cold air setups before, and I did feel a slight improvement in power, (but driveability sucked) but I got much better results (dramatic) by just having the filter under the hood, and fooling the air temp sensor to spit out cooler readings. I remember back when I was playing around with different resistor values, and if I got too high with the resistance, and the IAT readings got too cold because of it, my car would develop MAJOR tip-in detonation cause of the added timing. It sounds crazy, but its been proven time and time again with many EFI cars.
Does it ever feel like your car has lost 50 hp after it heats up? Throttle response goes to hell in a handbasket? Engines are supposed to make more power when they heat up. You lose the power because the computer is pulling timing from having high temp readings. And the retard wont show up on the scan tool.
Does it ever feel like your car has lost 50 hp after it heats up? Throttle response goes to hell in a handbasket? Engines are supposed to make more power when they heat up. You lose the power because the computer is pulling timing from having high temp readings. And the retard wont show up on the scan tool.
Good to know. But, for warranty purposes, they have to have some means of pulling timing before detonation even starts. Its usually a value that comes from matching the coolant temp readings with the IAT readings, and the base spark curve is pulled down a few degrees. Then if detonation is sensed, it pulls even more. For GM to not do this would be strange, given that all cars have some means of pulling this off.bruce said:
VadersV6 said:
The IAT timing isn't used in the TR, you can mount the sensor anywhere you want and it won't effect the timing due to anything in the chip.
If you want to doctor the IAT to change the MAF correction, fine, but that's fueling.
The tip-in problem generally is from the chip being off to begin with, typically the *chip gurus* use the same timing table (other then WOT) for EGR, and non-EGR applications, which is a lot less then optimal. Not to mention few folks bother to actually tune the delta TPS AE or MAF AE tables.
As far as what shows on a scanner, mine shows all 255 memory locations for what's going on. So you *won't show* statement is not usiversally true.
Not trying to pick on....
VadersV6 said:
Show me where in the code this ability exists.
I've spent some time on this subject, and there is no way in the TR code for the ecm to *pulling timing before it starts*.
Just to be specific, I've looked at both the PROM, and ROM, in very close detail and just haven't seen what you're claiming exists.
I said "it's good to know" that it doesnt exist in the TR programming. It does exist with other EFI late model cars though. Practically all of them. It would only seem logical that GM would have created a base timing retard when things heat up, unless warranty claims didnt concern them. It sure concerned everyone else...or maybe it was just too early on in the EFI world for them to have thought of doing that. Would they have any means of doing this other than coolant temp readings and IAT readings? So the IAT readings alter MAF correction? Could that have an effect on timing? Ive seen timing change via altered MAF readings. Could that be how its done?bruce said:
Why is it that I'm getting KR at lower boost levels ever since I put in the different thermistor? My BLM's havent changed. O2 readings at WOT havent changed. Too bad I have no means of looking at my timing so I can see first hand, although I do take your word for it.
VadersV6 said:
*Base timing Retard*?.
Geesh, are you asking now, or stating things as fact.
There is a IAT/MAT timing table. It's easy enough to populate and experiment with if you want.
The IAT fueling correction has no effect on timing.
If you want to know what your car is doing, then get the equiment to do that. While rather simplistic, Direct Scan will allow you to log and review what your engine is doing. If you really want to understand what's going on, then building an ecm bench, and using something like lockers is the way to go. Then you can accurately see the difference from *theory* (what looks to be happening) to actual.
BTW, this is a TR Board, so what other ecms and brands do is immaterial for this Tech Section.
fontana said:
None that I've found.
There's no timing code related to TPS, other then the WOT timing. It's enable is generally about 60% TPS, when it's used. Most folks disable it like they did in the TTA code by setting the enable to 99%.
The *tip-in* problems are generally (if not always), AE (Accleration Enrichment) related (if not maintance related). Too lean can generate detonation, and that can generate some timing being pulled out.
Again, it can get back to the spark table, ie without EGR less total advance is needed, and thus the initial off idle timing would be effected by a redo of the timing. ie, with less low load timing, it would also in effect be ramped out quicker as the LV8 increases. (LV8= the way a MAF system, creates a load related air flow to RPM calculation).
My interpretation from other posts AND from viewing IAT/airflow adjustment tables is that the IAT on the TR is used only for MAF correction. By it's design, the original MAF is a temperature sensitive device (airflow is measured by a cooling effect). Extreme ambient temperatures will cause the MAF to read incorrectly, therefore the IAT is used to adjust the MAF reading for correction. Newer MAF sensors (LS1, etc) have an internal correction - newer design.
Tip-in timing retard is known as Burst Knock Retard or BKR. You can see the parameters for its operation starting at $3384.
$3384 BRR active time (the active time in a stock chip is .1 sec)
$3385 TPS delta threshold to activate BKR (this is 9.8%)
$3386 BKR retard for active mode (this is set to 7 degrees)
$3387 if coolant less than 40 C skip BKR
$3388 if MPH > 50 skip BKR
The code to process this starts at $E5C3
HTH
Wayne
$3384 BRR active time (the active time in a stock chip is .1 sec)
$3385 TPS delta threshold to activate BKR (this is 9.8%)
$3386 BKR retard for active mode (this is set to 7 degrees)
$3387 if coolant less than 40 C skip BKR
$3388 if MPH > 50 skip BKR
The code to process this starts at $E5C3
HTH
Wayne
Bruce- its possible that there are some aspects of EFI tuning that you havent seen firsthand. Because you havent seen some particular ECM strategy, it doesnt mean it doesnt exist. Its very possible that there is no retard that comes from heat soak on the TR's. You didnt think there was any tip-in retard, and apparantly there is. The same could go for heat soak. An engine is far more likely to detonate at high air and coolant temps. The GM engineers knew this. They knew that this is a turbocharged motor, which increases the need for such a feature. They knew that decreasing detonation makes warranty guys happy. Its makes the EPA happy. I didnt say this feature "has to" exist on the TR's. I said its common among EFI cars, and if its not on these ones, then it would be surprising...but it would be possible. Scottyb makes a good point, and does it without any condescending tone. I'm not slamming your knowledge. I just think that there are features hidden way in there that alot of people may not know about.
I found this on a site discussing old FI F-body cars:
Q: Why and how should I relocate my idle air temperature (IAT) sensor?
A: The stock position of the IAT sensor (in the rubber intake elbow just before the throttle body) causes it to pick up a lot of intake manifold heat. This can be an extra 10 degrees F at highway speeds and 30 degrees F (or more) at idle. This causes the computer to retard the timing (zapping power) and causes the engine to run overly rich (since the MAF thinks there's more air going through it than there really is due to artificially high temperatures). By moving the IAT towards the air filter (away from the hot manifold), the ECM will get a more accurate reading of the actual intake temperature and will properly adjust the timing and fuel/air ratio. There's no need to worry about the air heating up more as it passes beyond the new location of the IAT since at wide open throttle, it takes the air 15/1000 of a second to travel from the air filter into the engine.
Q: Why and how should I relocate my idle air temperature (IAT) sensor?
A: The stock position of the IAT sensor (in the rubber intake elbow just before the throttle body) causes it to pick up a lot of intake manifold heat. This can be an extra 10 degrees F at highway speeds and 30 degrees F (or more) at idle. This causes the computer to retard the timing (zapping power) and causes the engine to run overly rich (since the MAF thinks there's more air going through it than there really is due to artificially high temperatures). By moving the IAT towards the air filter (away from the hot manifold), the ECM will get a more accurate reading of the actual intake temperature and will properly adjust the timing and fuel/air ratio. There's no need to worry about the air heating up more as it passes beyond the new location of the IAT since at wide open throttle, it takes the air 15/1000 of a second to travel from the air filter into the engine.
The old F body cars my have had a different ECM from the early Buicks, and a different MAF, I believe. It's risky to try to extrapolate things from other cars to the turbo Buicks, because they were pretty unique, and the team that put them together did NOT work on Corvettes or Camaros or Mustangs. The "tip in" timing that Fonatana mentions is the rate at which detonation induced retard is removed. Once knock is sensed, and knock retard is used, then it is removed at a rate controlled by these parameters. And, as Scotty b mentions, the Buick MAF is not temperature compensated, unlike the later MAFs, and depends on the MAT (or Inlet Air Temp, if you prefer) sensor to adjust the readings for extremely hot or cold air into the MAF.
The "look up" tables for the ECM are pretty small, and readily available, to it's pretty easy to look through them, from end to end, and see whether there are, or are not, timing changes based on the IAT/MAT. I haven't looked, but Bruce has, and until somebody else answers his question as to "where", I am going to believe what Bruce has told us.
The "look up" tables for the ECM are pretty small, and readily available, to it's pretty easy to look through them, from end to end, and see whether there are, or are not, timing changes based on the IAT/MAT. I haven't looked, but Bruce has, and until somebody else answers his question as to "where", I am going to believe what Bruce has told us.
Tip-in timing retard is strictly a function of delta TPS threshold. I think you think that knock is sensed and then the timing is retarded using the tables I presented? This is not the case. Or maybe I didn't understand your post. Just trying to be clear 
Wayne
Wayne
Ive continued to look around on the net for some sort of strategy like this on older GM cars, and it seems like everywhere I look, they mention some means of pulling timing based on temperature. But, given that I have no real solid data to back it up, I humbly concede, until I find something real. It seems like it would be a major oversight to not do something like this, since it would add an extra layer of insurance against detonation and warranty claims for blown motors. Maybe GM simply made the most out of what they had at the time.
Wayne- do you live in Fontana, Ca.? Or is it something else? I had a GN cruising next to me going from the 15 to the 60 a couple weeks ago at night, and given there arent a whole lot of GN's in that area, maybe this could be you. Its a long shot but had to ask.
Wayne- do you live in Fontana, Ca.? Or is it something else? I had a GN cruising next to me going from the 15 to the 60 a couple weeks ago at night, and given there arent a whole lot of GN's in that area, maybe this could be you. Its a long shot but had to ask.
