IAT effecting IAC steps. How?
09-19-2007, 03:40 AM
#1
TECH Resident
Thread Starter
IAT effecting IAC steps. How? I've put new heads and cam on the car and doing an SD tune, the normal driving cells are almost spot on now.
Fuel trims are off, OL enabled.
I parked up, my idle AFR = 14.0:1, IAT = 60deg, RPM = 900, IAC = 40, InjDuty = 2.0msec, ECT = 178, MAF = 10g/sec
so I'm okay with that, just need to tweak that idle cell on the VE map.
I leave the car ticking over for a few mins, IAT rising.
Looking at the readings I now have.
AFR = 16.5:1, IAT = 100deg, RPM = 900, IAC = 70, InjDuty = 2.0msec, ECT = 178, MAF = 11g/sec
Why does the Idle Air control open up when the Intake Air Temperature rises?
I have looked at the tables, many fueling and Air tables depend on the ECT, but ECT has remained static during the test. It must be in the PCM somewhere to open up the IAC when IAT rises.
Havn't got the logs with me, will post them later, its a 20min or so log, which about a 5 mins idle in the middle, you can see the IAT, AFR and IAC rise together.
Fuel trims are off, OL enabled.
I parked up, my idle AFR = 14.0:1, IAT = 60deg, RPM = 900, IAC = 40, InjDuty = 2.0msec, ECT = 178, MAF = 10g/sec
so I'm okay with that, just need to tweak that idle cell on the VE map.
I leave the car ticking over for a few mins, IAT rising.
Looking at the readings I now have.
AFR = 16.5:1, IAT = 100deg, RPM = 900, IAC = 70, InjDuty = 2.0msec, ECT = 178, MAF = 11g/sec
Why does the Idle Air control open up when the Intake Air Temperature rises?
I have looked at the tables, many fueling and Air tables depend on the ECT, but ECT has remained static during the test. It must be in the PCM somewhere to open up the IAC when IAT rises.
Havn't got the logs with me, will post them later, its a 20min or so log, which about a 5 mins idle in the middle, you can see the IAT, AFR and IAC rise together.
Last edited by RedWS6 00; 09-19-2007 at 07:37 AM.
09-19-2007, 09:22 AM
#2
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You have some engine load factors that are indexed by IAT
(A/C compressor torque, for example). Your motor gets tighter
with temperature (piston expands to sleeve, etc.) and may
have higher real operating drag torque when hot. But seeing
the mixture swing to that degree may be the more important
thing, maybe that lean is off your "peak efficiency" torque-
per-cylinder-air-charge and you make up weakness with air
volume.
Since you see this strong IAT sensitivity you might be a good
candidate for relocating the IAT (more into the air stream, or
out of it in the ambient entirely, try stuff out) to see what
gives the greatest consistency of fueling across weather
conditions. Open loop speed density has a high dependence
on incoming air temperature (in calculations and in fact, the
question being how to get the two to maximum agreement).
(A/C compressor torque, for example). Your motor gets tighter
with temperature (piston expands to sleeve, etc.) and may
have higher real operating drag torque when hot. But seeing
the mixture swing to that degree may be the more important
thing, maybe that lean is off your "peak efficiency" torque-
per-cylinder-air-charge and you make up weakness with air
volume.
Since you see this strong IAT sensitivity you might be a good
candidate for relocating the IAT (more into the air stream, or
out of it in the ambient entirely, try stuff out) to see what
gives the greatest consistency of fueling across weather
conditions. Open loop speed density has a high dependence
on incoming air temperature (in calculations and in fact, the
question being how to get the two to maximum agreement).
09-19-2007, 01:25 PM
#3
TECH Resident
Thread Starter
Thanks Jimmy, I think relocating the IAT sensor may be a good idea, it sits abovt the radiator in the Whisper Lid, perhaps moving it to the MAF housing may be a good idea.
Attached is the HP Tuners log, config and the bin.
Had to rename the .CFG file to HPL so I could attached it, you will need to renamed WB_SD_TuneC.HPL back to .CFG. YOu only need the CFG as its got the WB formula in it.
At frame 3100. I park up and the AFR is around 13.9:1, IAT is 66. Left on idle till frame 5500. AFR is over 17:1, and IAT is 122. The ECT is always 178 throughout this period, and idel is stable.
Attached is the HP Tuners log, config and the bin.
Had to rename the .CFG file to HPL so I could attached it, you will need to renamed WB_SD_TuneC.HPL back to .CFG. YOu only need the CFG as its got the WB formula in it.
At frame 3100. I park up and the AFR is around 13.9:1, IAT is 66. Left on idle till frame 5500. AFR is over 17:1, and IAT is 122. The ECT is always 178 throughout this period, and idel is stable.