Change in afr reading | AEM
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Graham
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Last seen: 5 years 11 months ago
Joined: 07/19/2014 - 17:59
Change in afr reading

4 or 5 years ago, I installed an AEM analog afr meter on my 72 V-8 Mercedes. It has worked well and allowed me to adjust and tune the electronic fuel injection system. 

The gauge readings have always been consistent. However, this year I noticed that the afr readings had changed and are now high by about 0.7 to 1.1. This is true at both idle and under load and these conditions are controlled by separate circuits and have separate adjustment methods. In other words, it is unlikely that an engine mixture adjustment has changed.

Before I spend more time trying to find the cause, I wondered if this could be a gauge or sensor problem? Is there any way to do a check short of buying new parts?

 

AEM_PT
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Last seen: 2 months 2 weeks ago
Joined: 05/22/2014 - 08:13
Hi Graham,

Hi Graham,

The issue you may be having is likely related to the sensor. The life expectancy is 50-80,000 km. You can do a rag test on the sensor to check if it still sweeps between rich and lean mixtures normally. Key On Engine OFF, Remove the sensor from the O2 bung and let it warm up. Get a rag, spray some brake cleaner or put fuel on it. Cover the sensor with the rag and the "---" reading on your gauge should go from full lean to full rich. Should the sensor not respond as intended, it may need to be replaced.

Graham
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Last seen: 5 years 11 months ago
Joined: 07/19/2014 - 17:59
The sensor is in kind of a

The sensor is in kind of a tight position under the car, so I will only do that if under for some other reason!

But the sensor does respond to changes in AFR. For example, on cold start up, the car always is rich (~9-10) and because there is a fuel cutoff when coasting, it swings to full lean if I take my foot off pedal. Same, if I allow meter to warm up but don't start car, it will read full scale lean.

The problem appears to be that the meter is either reading higher than it once did. OR, my car is running leaner. I will do some more checking.

By the way, mileage on car is likely only about 8000 miles since meter was installed.