AEM erratic AFR readings
 

My AEM with the Bosch LSU 4.9 reads erratically, as in the AFR jumps around from, say, 12.x to 14.x almost instantaneously, at steady-state throttle conditions. I know it will go from semi-normal AFR to high AFR when I cut the throttle, which is normal. I have been running in open loop on my SDS EFI. I am on my third LSU 4.9 sensor; they all exhibit the same properties. Engine always seems to run rich, by using the old school farmer methods of checking the tailpipe, plugs, fuel consumption, etc. I changed the injectors from 44# to 30#, got a predictable change in the duty cycle. This did not change the erratic readings.

I am really annoyed by this. These AEM are reputed to be a pretty good gauge. I am having difficulty understanding how the AFR can jump around so much. I realize the EFI will change fuel delivery pretty quickly, but even as I watch the duty cycle stay at a constant value, the AFR changes very quickly. This doesn't make sense to me. It has done this with the turbo engine, and with the NA engine

Tomorrow, I will try running in closed loop, and see if anything changes. I believe that closed loop is user defined over a variable RPM range, so I'll see if I can dial it in and observe from there. I may have to hook up some sort of data logger to analyze this further.

Question is thus: has anyone else seen this behavior? I distrust the AEM gauge and the LSU 4.9 at this point. But, it is all I have at the moment. I may have to break down and bring it to a tuner with a dyno and CO meter.

The early AEM AFR gauges are known to go bad . I think the fixed it in 2018?
FWIW
ian

I've had the same AEM unit in place for 6 years now....not even a lambda change. Works perfectly.
This is the 'analog' type with a needle not a number read out.

Th Ballenger AFR500v2 is the best Lambda sensor I have used....and I have the AEM too:

https://www.bmotorsports.com/shop/product_info.php/products_id/2337

The NTK sensors are better than the Bosch but they are more expensive.

Pat, I have a first-gen handheld AFR meter I can send down to you if you want to get another opinion on your true AFR. It has its own O2 sensor and cable, the meter is powered by the cigarette lighter and you run the cable outside the car through your window and hold the meter on your lap to watch the digital LCD readout while you drive. Worked the last time I used it a few years ago.
LMK if you want to borrow it.

https://www.suprastore.com/inlmwidiaiki.html

Pat,
If you've had the same results with both your turbo and NA cars....it is likely a defective meter.
When tuning up a new engine or EFI system......I often kill the Bosch sensors..............and before they die, they lie.

regards,
al