I know this has been talked about before. I wanted to bring what I thnk is more support to this out. The fact that it appears there is files we do not have acess to in HPT. I tuned a 99 Sunfire GT with a built 2.4 N/A. After the tune the guy started having issues with it stalling when coming to a stop. He insisted it was the tune (I did not feel it was). He ended up unplugging the O2 sensor and the car stopped stalling. Yesterday we got back together. I hooked HPT up and did some datalogging. Car would not stall (did get close a couple times), but never stalled. After playing around for a while got the car to start stalling, and also noticed the IAT's were off. I switched IAT's and they then seemed normal, and it stopped stalling. hmmmm. Switch IAT's back to orginal, also seemed to be normal and fine. After a while IAT's would get stuck, and stalling would come back. Checked the wiring on the IAT (it had a section replaced at one time, but was connected nicely). You could mess with the wiring/connection and temps would start moving.
So it appears this car has a issue with the IAT sensor wiring, or connection. When the IAT's get stuck it wants to stall when coming to a stop. If you force the car into Open Loop and runs fine no issues.
So my point in the post is it appears that IAT temps play a part in more than just the timing table (or timing retard on high temps we see). Maybe a fueling table with IAT's we can't see????
Also in the process of messing with the wiring I touched the bare wire of the IAT to metal. This caused the IAT to jump to 304F. When this happened the car's RPM's bogged down. Even holding the idle at 2k doing this the RPM's bogged down.
Any thoughts? Maybe I'm reading this wrong?
Also wanted to add. I know that with auto cars if the IAT is not connected it caused a bad/hard shifting of the tranny, which also leads me to think more files we do not see.
FU Tuning
I agree that the IAT likely has more effect than just timing. My reasoning behind it is that it doesn't seem to matter what temperature it is outside (-25C or +25C) the AFRs in open loop (start up, etc.) are much the same. You'd think the colder the air the leaner the AFR. I think the IAT compensates for the temperature change by use or some sort of multiplier that's applied to the fuel tables. I haven't compared logs but I suspect its much the same if you look at the AFRs in PE mode as well. I know in closed loop the O2 sensor makes the adjustments but what about open loop situations? I just don't see how the car can run equally well in winter without adding fuel based on air temperature.
Sorry guys HPT already has your money. No extra tables exist, and a 1000 megawatt nuclear reactor does not exist a under the Pentagon!
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HP Tuners | Innovate WB02 | Spec Stage 3 | Team Green LSD | TurboTech Upper | Full Addco Sways | Sportlines & Yellows |
Will be watching this thread John
I would think (with the GM reflash) there would be some iat affected fuel tables. The air temps get way above ambient, so there would have to be some measure of control using the iat sensor.
You bring up a important topic. I've noticed temp reading of any sorts at least on some GM cars is crucial in order to run right. A little off the car in question but same track but a Saturn (automatic) I fixed that love to stumble every corner or stop light was fixed when I changed the water temp sensor. Odd in IMO.
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-----The orginal Mr.Goodwrench on the JBO since 11/99-----
Well AFR is affected by coolant temp. That is a file we can see and adjust. SO I see and understand that.
It use to be a old saying to put your IAT in colder air to dump more fuel in the motor for power. That was in the early days of JBody modding. now we know GM runs our cars rich, but yet there target AFR is very lean.
FU Tuning
There at the very least is an IAT multiplier for fueling. Otherwise, as mentioned, summer and winter would require different tunes. So far from about 20*F-60*F, my car holds PE AFRs within 0.3:1 from 3000-7000rpm. The table/timer i'm most interested to see is the one that causes the commanded AFR to drop after a certain period of WOT. I've already corrected the RPM multiplier to 1.0000 across the range, and it still drops inconsistently...
IAT is use to calculate the mass of the air entering the engine. There is no room for arguement there. It has to be that woy or the engine cannot run properly
Cold air at 10% throttle and 2000 rpm has more oxygen (denser) than hot air at 10% throttle and 2000rpm (less dense). The IAT is the correction factor to keep it fueled right in both extremes..
HP will never give access to those tables because they really never change much, so 99.999% of their customers would not use them anyway or at least not need to use them.
The biggest issue for us with that is forced induction. FI raises IATs while also increasing air density (pressure) while the PCM is only programmed that higher air temp = less dense air. Although it is even unlikely that access to those tables could even help you in that situation anyway since the application is NA so GM didn't likely reference those tables to MAP so that the trend could even be programmed to reverse itself as pressure went up. Instead, a singel 1bar correction factor would be hard programmed into the cal.
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