986 Forum - The Community for Porsche Boxster & Cayman Owners - View Single Post - Please confirm my diagnosis of one bad O2 sensor

Timbert · 11-07-2015, 05:22 PM

So I have now replaced both front O2 sensors with Bosch and eliminated the "resistance limit" warning so my O2 heaters are working. According to the "DME setpoints" pages in the factory manual several values are still out of spec:

Mass Air Flow is between 17.5 and 18.5 when it's supposed to be 15 +/- 1.25.
Ignition Timing is 3.8 to 9, supposed to be 5.3 +/- 0.5
Spec. air mass is 11 to 12, supposed to be 15.5 +/- 0.25
Spec. air adaptation is 0, supposed to be 1.5 +/- 0.05
Injection time is 2.6 to 3.7, supposed to be 2.2 +/- 0.1

But now the 02 sensor voltages no longer swing up and down, and the fuel trims are at the baseline. The idle is smooth, but shouldn't I be seeing O2 sensor voltage swings? I have two different MAF sensors, either of which MIGHT be good or bad.

When I remove the oil cap the fuel trim levels do not change, as the example in the manual indicates they should. I am stumped, can anyone help?

11-07-2015, 05:22 PM	#4
Timbert Registered User Join Date: Sep 2015 Location: Phoenix Posts: 15	Need Durametric MAF/O2 diagnostic help So I have now replaced both front O2 sensors with Bosch and eliminated the "resistance limit" warning so my O2 heaters are working. According to the "DME setpoints" pages in the factory manual several values are still out of spec: Mass Air Flow is between 17.5 and 18.5 when it's supposed to be 15 +/- 1.25. Ignition Timing is 3.8 to 9, supposed to be 5.3 +/- 0.5 Spec. air mass is 11 to 12, supposed to be 15.5 +/- 0.25 Spec. air adaptation is 0, supposed to be 1.5 +/- 0.05 Injection time is 2.6 to 3.7, supposed to be 2.2 +/- 0.1 But now the 02 sensor voltages no longer swing up and down, and the fuel trims are at the baseline. The idle is smooth, but shouldn't I be seeing O2 sensor voltage swings? I have two different MAF sensors, either of which MIGHT be good or bad. When I remove the oil cap the fuel trim levels do not change, as the example in the manual indicates they should. I am stumped, can anyone help?