I am almost positive its the aem gauge itself. I just junked the one I had because of the same issue. I have had 3 bad units in the past 5 years. Good luck bro.

 

I'm running into the same issue...under WOT WB reads 10.9's- low 11's..datalogging shows AEM reading mid/high 11's. I read the 02 should be in th .96-1.00 range to be set up correctly. I found I had to adjust it as low as .78 to get the AEM and WB AFR's to correlate at idle...then while I start cruising the difference grows as if the AEM isn't getting enough gain to keep up with the WB.

Friday I'm going to measure the voltage at the gauge and set the gain on the AEM to match it...would it be ok if it's not in the .96-1.0 box? I've checked the grounds/connections/wiring...all is good to go. What are ya'lls 02 gain set to? Thanks.

 

Has anyone wire the wideband to battery??? Ground to the battery and power coming from the battery switch with a relay??? You need to do that.

 

Mustang guys have the same issue....

best thing we've found is make sure the wb02 and ems have the same power/ground wires... and run a 10-12ga ground wire from the negative side of the battery directly to the ems ground.

Some guys have used 0-5v potentialometers to "dial in" the gage... they hook it up to the harness on the wb, and go through the voltage range and calibrate the table that way...this way you know it's spot on... I'm starting to think that the voltage cal table aem provides isn't correct..