Open loop vs Closed loop AFR


Apr 28, 2004
Hi All,

I've been trying to chase down a high AFR reading for some time...initially it was caused by a bad sensor which seemed to fix it...partially. My combo is as follows:
- 60Lb injectors with TT 6.1
- PLX wideband
- PowerLogger
- 3.5 inch MAF and Translator
- Stock intake/heads
- TE 60 Turbo
- Cottons Front mount intercooler

I've noticed that my AFR hovers right around 12.5-13.5 when in open loop (observed at engine startup) and then as soon as it goes to closed loop the AFR jumps to 15, and when I begin to give it throttle the AFR continues to rise to as high into the 17s. The more immediate the throttle I give it the quicker it leans out.

Is there something obvious that is going wrong here? Are there parameters I need to be tweaking in the my TT chip fueling to prevent the rise in AFR?
Is there more information I should be providing in order to diagnose this problem?

One other question, not sure if it is related. I have both the stock O2 sensor and the Wideband O2 sensor installed. Does the stock serve any purpose aside from plugging a hole with this chip?

Stock o2 will be used until 70% throttle, then the wideband will kick in and the chip will use the wideband for fueling correction. The open loop is pre programmed and will run the car richer until the car is warm. Once warm it starts using the closed loop and is using the stock o2 to run the car. The afr readings you posted are identical to my car with a 6.1 chip and plx wideband. What are your scanmaster readings?
I ran the car for a couple minutes to try and recreate the condition while in park. attached are the powerlog files i was able to record...does this help at all? What other readings from the scan master would be helpful...IAC is right around 30, TPS is right at .42...anything else that would be helpful?


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