Paul scanner Video

Dear Paul,

Thank you very much for teaching us how to diagnose. Personally, I learned too much from you and I do thank you from the bottom of my heart.

Regarding one of your video on youtube

when you do WOT, I see too much lean and rich activity on your O2 sensors but the fuel trims are ok....Time on video 14:35.


Is there any clarification for this?
I have been hunting for this answer long time ago but I have not got any answer.



Hope you reply to me.


Have a great day.

hi could we get more precise info on your problem with scope shot maybe lacking a little info

The way I interpret this is that the job of the short term fuel trim is to keep that o2 sensor oscillating above and below a half a volt at any rpm range. (Or fuel cell).
Also remember, that this wasn't a WOT pull. This was in park, @ 2500rpm (at the time marker you referenced), so there wasn't any call from the PCM for enrichment like there might be if you were passing a truck on the highway.

I think you're thinking of some other MAF tests where on a wot pull, Paul looks for the upstream to stay rich.
A lot of the time, at wot, the pcm will go into open loop or open loop drive mode. That's when you'll see enrichment for power, the fuel trims won't be relevant because of open loop status, and the up stream sensor would hold rich.