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AFR differences - which to trust?

Understanding AFR

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I've noticed that my dyno AFR readings are a bit different to my AEM UEGO wideband readings.

Now before you assume that it's to do with the location - I loaded the car up on the dyno and noted down the reading on the gauge inside my car. I then disconnected the sensor from the controller in the car, and connected the dyno controller to the sensor mounted in the car.

Now the reading I got from my AEM unit was 11.0, however the dyno showed 11.7. I was also able to test this by using tailpipe sniffers for both the dyno and the AEM units at the same time. Same sensors and same location, yet different AFR readings. I even swapped sensors around between the units to eliminate a faulty sensor.

Dyno manufacturer says that their controllers don't require calibration and customers generally don't question the accuracy of these. As much as I'd like to just accept his answer and move along, I am just feeling slightly unconfident by this situation. Especially when tuning rotaries!

Is there a way of testing these controllers/sensors to determine their accuracy? Has anyone else been in this situation? How have you overcome this?


Wow that is a huge difference. I can understand why you're concerned and I don't blame you.

What controller is fitted to the dyno?

I haven't used the AEM UEGO so can't comment on their accuracy.

Only real way to test is either measure the output voltage of the sensor vs the data sheet and afr reading or possibly get another controller and sensor to test with and see where that reads. Something like a Motec LTC .

Interested to hear anyone else's thoughts, especially if they have used the AEM UEGO

What controller is your dyno using? Which sensors are you using?

I don't tune rotarys but have had it hired out once to allow someone to tune their own, I just operated it and my dyno lambda did read different to their AEM. Unfortunately I can't remember which way it was but I think the AEM did read richer than the dyno in that case too.

I would invest in a secondary lambda controller, I have an innovate LM2 which I use for street/track work and have pulled it out to double check my dyno values compared to an installed gauge a few times just to rule out error.

The dyno has two controllers, both are Techedge. One is using a Bosch 4.0 sensor and the other is a 4.9 sensor. I had the controllers recalibrated to the dyno once again which were tested and working fine. It is only when I'm running the car on the dyno that both sensors are reading different from each other (approx 0.3 AFR), and different again from my two AEM units.

One of the AEM units is mounted in my car, and one as a portable unit. Both read very consistent to each other despite one being mounted in in the exhaust pre-cat and the other was used in a pipe sniffer.

I think that it may be an issue with the cable running from the controller to the sensor. I'll have to check voltages and resistance when I get the chance.

Thanks for your suggestions!

Anyone else had any experience/thoughts on this?

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