Idle LT trim high causing a rich AFR
08-14-2016, 03:34 PM
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Idle LT trim high causing a rich AFR I just installed a TSP 224/228 LSA 112 into my 2002 LS1 automatic Camaro. The Camaro is basically stock. I tune the base running airflow, primary VE and the MAF calibration tables. The car is running fine, but I notice the AFR dropping while idling. The AFR with the stock cam was about 14.5 at idle. With this cam, the car’s AFR drops into 13.5 range when it idles. When I drive the car, the AFR is around 14.4 and when I come to a stop the AFR is about 14.3. If I continue to idle it will drop to 13.6. The strange part is the reason for the drop in AFR appears to be an increase in the LT trims. They are about 2 when the initial idle AFR is 14.3 and then over time increase to 12 and the AFR drops to 13.6. I do not know why. I tried recalibrating the MAF at the idle air flow frequency, but it does not appear to have any effect. Any thoughts would be appreciated.
John
John
08-16-2016, 05:31 AM
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Yeah, long tube headers and cams with overlap can make the oxygen sensors read false lean. Then, no matter how much you tune the MAF or VE tables the lean readings will cause the ECU to add fuel.
Here's my method:
In the scanner, run in open loop and command 14.7 AFR. Look at the wideband. If it's reading 14.7, you're basically good in the VE table and MAF. Now, look at your mV readings on your oxygen sensors. Probably around 300-350. Maybe even lower. For this example let's say 300. Now, take note of your mass airflow and dynamic air flows. Now, in the tune, go to the airflow modes table and see what mode you're in. Probably 6,7, or 8. For this example, let's say it's mode 6. Go to your oxygen sensor switch points. Find the airflow mode cell you need and key in the mV readings you observed. In this example, it would be mode 6, 300 mV. Write the tune.
Here's my method:
In the scanner, run in open loop and command 14.7 AFR. Look at the wideband. If it's reading 14.7, you're basically good in the VE table and MAF. Now, look at your mV readings on your oxygen sensors. Probably around 300-350. Maybe even lower. For this example let's say 300. Now, take note of your mass airflow and dynamic air flows. Now, in the tune, go to the airflow modes table and see what mode you're in. Probably 6,7, or 8. For this example, let's say it's mode 6. Go to your oxygen sensor switch points. Find the airflow mode cell you need and key in the mV readings you observed. In this example, it would be mode 6, 300 mV. Write the tune.
08-16-2016, 12:25 PM
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I have come to the same conclusion that the "rich AFR" is the result the overlap of the cam even though it is only 2%. No matter how I adjusted the MAF table up or down, the AFR stays the same. Only the LTFT changed. I can live with this as the car runs fine, but I was happy to learn that I could adjust the narrow O2 switch point. Thanks Darth V8r. I reviewed your method and I understand the procedure and will give it shot.
08-17-2016, 03:08 PM
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I just run open loop full time and keep an eye on my perma-installed WBO2. Fuel trims aren't necessary. Run it a little safe (14.5) when you do your tune and rarely there'll be a day when you see 15:1 (if ever) assuming you tuned it right. Worked just fine for cars with carbs...
