I started troubleshooting an overheating in my '87 F-250 7.5l which I thought was because of a lean condition. I purchased an Auto Meter O2 sensor and it is showing that I am at an A/F of 18 (after the self calibrating and heating procedure that keeps the needle between 8 and 9).

I put new needles in the carb one step richer and the gauge again pegged out at 18. Went up another needle and this time I can smell fuel which is telling me that the engine is too rich. However, the gauge pegged out at 18.

So my question is this: Is this an acceptible place to mount the O2 sensor? I am short on locations and believe that there are no air leaks in the exhaust upstream from this gauge.

 

Uhh, are you actually running an open pipe two inches behind the sensor?

 

Yep. Would that lead to bad values? Recently rebuilt the engine I have not had a chance to get the exhaust done yet. I figured the flow of exhaust over the sensor would keep the fresh air away from the sensor and still read in the ballpark.

 

Having the sensor that close to the end will cause it to read very lean, which it is.

Do you have a couple of feet of any sort of pipe that you can temporarily put on the end? Even if it kind of "hangs" on the end, it will help. So long as it is "closed" on the end closest to the sensor, it should let you know that the sensor and gauge are working even if they aren't completely accurate yet.

 

Reporting Back:

24" of pipe after the sensor did the trick. Thanks!

 

Excellent! I'm glad to hear it.