Truck seems like sometimes it has good power, and other times it feels like i'm driving a Geo Metro.

In a prior thread I asked about my cat, in this thread I've hooked up my scan tool and graphed my O2 sensors as I drive. In the video below I'm on the highway, at about 65 with a steady throttle until the end when I take the exit.
It looks to me like the entire time I'm cruising it's running rich? I'm a novice when it comes to O2 and Air fuel readings so maybe someone here with more experience can tell me if this graph looks... normal?


And this is sitting in park at about 1500rpm



Edit - I should add it's got factory intake, new air filter, no TB spacers or anything. Copper plugs put in about 15k miles ago

 

Well, the O2 sensor sure thinks it's running rich....... Why the PCM isn't compensating is a mystery to me. Would be interesting to see what short/long term fuel trims look like while cruising.

 

Ill get that info for you a little later today

 

And here's those fuel trims
Down at idle at a red light

And this is following that same highway route I did before

..And for ishts and giggles, here's the B1 S1 volts vs B1 S1 Short Term Fuel Trim on the same highway route (video starts up when I enter the highway)

I also ran a back pressure test using the upstream O2 port and I saw no meaningful pressure. 0 PSI through 3000 RPM with slight fluttering as I let off the gas, maybe 0.25psi worth.

Here's the upstream O2 sensor
https://i.imgur.com/HiYAj3l.jpg

I don't have full history on the truck but I'd bet dollars to doughnuts that's the factory O2 sensor. Maybe I'll drop a couple new ones in and see how she goes.

 

Has the computer been tuned?

 

Hmm unsure, it's an 03 so options are limited for it. If it's tuned it came that way from the seller.

 

I usually also look at vac and map to see more of the picture. And I pick two steady states, like idle and 2000 rpm. Snap shot more or less data, the data logging is usually for things that don't present in the steady state. I'll typically be more concerned about LTFT.

 

I don't have a vacuum gauge on me but here's map and LTFT at idle and 2000 rpm

idle



2000 rpm


Craking event (fuel pump disabled)


And starting event







How can I be drawing more vacuum at 2000rpm? I thought as throttle increased vacuum should decrease?

 

MAP is measuring manifold vacuum. Higher the number, the lower the pressure in the manifold.

 

Our sensors measure pressure in inHg Absolute (inHgA), which makes that statement demonstrably false. So, I'll demonstrate.

Here I've removed my MAP sensor from the manifold and attached it to a vacuum pump with an inHg gauge.


As you can see, the inHg gauge reads zero, no vacuum.


The scan tool confirms that at 0 inHg (physical gauge) the sensor reads 30inHgA (sea level)


I draw 15.5inHg vacuum on the sensor


Map sensor reports pressure has fallen from 30 inHgA to 14 inHgA


Draw the vacuum down to 20 inHg vacuum


And the sensor reports 9 inHgA