I have been battling a once intermittent problem that is now repeatable all of the time. Without going on a rant about the vehicle the basic problem I am having is with intermittent STIT demanding unrealistic amounts of air for the conditions.
Example: Car is idling in park , AC off. At operating temp the stit is pulling around 9g/s from my base settings in an attempt to trim the idle down. I have not fully dialed in my BRAF tables and I do have excess air in them at the moment. If a load is applied to the engine at idle, say turning on the AC, or moving the gear selector to Drive. The PCM instantly starts demanding positive STIT at a very fast rate. It will max the stit out at 30g/s until the vehicle stalls ( Iac reaches 310 counts very quickly). The idle desired airflow numbers go from about 10gs at idle to wanting over 25g/s in gear and instantly maxing out the IAC, with no pickup in RPM. Almost as if an absurd load is being placed on the engine. This is now a consistent problem that I can repeat sitting in the parking lot 100% of the time.
The previous day of tuning this problem was intermittent. On the same tune file, I could idle the car in GEAR, with AC ON, electric fans on, and it would trim about -6.5gs out of my stit in gear idle. Meaning on this current tune file, and nothing changed mechanically, this vehicle was able to idle under those same load conditions and the PCM still wanted to trim air OUT.
I am proficient in diagnostics but with this problem I feel like I am not sure which direction to take. What would make the PCM demand insane unrealistic amounts of desired air flow just from turning the AC on, or putting the car in gear one time and not the other? Five minutes later at the next stop light it will start pulling air again and acting normal under those same conditions. I find it hard to believe that my AC compressor, and/or transmission are BOTH applying unruly loads to the engine, as I can replicate these problems without one or the other. Any input would be great. I attached a log file showing the vehicle from cold start in park to hot idle in park. The STIT shit the bed as soon as I put the vehicle in gear. Remember the BRAF tables for in gear are not far off for testing purposes, under normal working conditions it will pull roughly -6 to -7gs out of my airflow with the ac on in gear, except when it decides to shit the bed and add 30+gs for no reason. Has anyone seen this?
I am an entry level tuner but I have since handed over the reigns to a more experienced remote tuner who also has said he has not ran into this problem. Any direction would be amazing.
I attached 2 logs, and the current tune file which is still being worked on but came to a halt with these current issues.
"Problematic Log" - Shows how the vehicle is able to operate with ac on in gear and want negative stit...............this log will also show how it randomly wants to max stit positive under those same conditions.
"Stit ok in park Log" Shows cold start to warmup in park - Soon as the shifter is moved to gear STIT throws a shit fit and maxes itself out.
I have done basic misfire diagnosis, unmetered air leak checking, basic compression and leak down testing, I have swapped throttle body/iac combos and pcms with other units we have in the shop since it was quick and easy checks. I also have ran the car in SD with no MAF to rule that out as well. Anyone?
Doesn't this link refer to ETC Scalar tuning for DBW applications? Excuse me if I am wrong. This application is a GEN3 DBC vehicle and it doesn't look like the same techniques apply?
edit:
Also , my problem does happen with the AC completely out of the equation. Just putting the car in gear A/C off will trigger the STIT to go nuts.
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