Strange lean condition

[ostrich]

I was tuning the car yesterday for full throttle and some part throttle driving. Everything was going well as I was tuning using the AFR Error. I pulled in the driveway, re-flashed the PCM with my new VE table and the car then started to run really lean even at Idle. This happened once before as well. I then re-flashed the PCM with my previous Bin and it still ran lean whereas it didn't the previous drive. Not sure what happened? Can someone take a look at my logs & Bin, can't figure this one out.

383 SBC
EFI Connections LS1 conversion
Heads
CompuCam
Exhaust etc

[DSteck]

Heat soak. Go drive it and you'll see it come back in line.

[ostrich]

Will do. That would explain things, I was on it for about 1hr tuning. Just surprised heat soak would cause that. I will post back with results. Thanks

[flame]

To avoid heatsoak scewing my logs I always pop the hood open when I am reviewing/changing the tune. Then start driving and get the IAT back to where it was in the previous log before I start the next log. Otherwise you will continue to chase your tail.

[DSteck]

To avoid heatsoak scewing my logs I always pop the hood open when I am reviewing/changing the tune. Then start driving and get the IAT back to where it was in the previous log before I start the next log. Otherwise you will continue to chase your tail.

Yep. This is good advice.

[BigMike42]

I noticed this even with maf tuning...I guess the PCM still uses IAT in the calculation even in maf only mode.

[JamesLinder]

You may want to make certain you did not defeat the purpose of the table that retards timing for various IAT values on the SPARK tab. GM was a little over protective with the values they entered into this table, however you should not zero this table out because it does protect against knock when your engine is heat soaked and this happens all the time when at stop lights during the summer.

[ostrich]

Bingo, heatsoak. That's what it was. I let the car cool down and everything is back to normal. My IAT sensor is a little different than an LS1 one. Basically I have a screw in one that goes into my aluminum intake (basically an LT1 intake). Looks very close to an ECT sensor. It sits half way back in the intake, takes a lot of heat. I have read alot of posts for heatsoak problems, so I'm going to relocate the sensor into the air intake track. Should be easy I have aluminum piping coming up to the throttle body. Also looking at the Cylinder Charge Temp Bias table. Looks like people are having success changes it's value to 1 across the board. May try this as well.

Thanks to every one who responded.
Appreciate the help from all the 'Senior' tuners.