P0420 code problem

[Kurtis West]

I've got an 07 1500 5.7 QC 4x4.

She's got roughly 181k miles on her.

For about a year now I've had an intermittent cel for P0420.

I've done a spark plug change, ran system cleaner, reset ecm, used an infrared thermometer and live data feed to try to diagnose it.

Both infared and the LD show the cats to be operating at proper temperature.

LD shows that the 02 sensors seem to be OK. However I did notice that the B1S1 seems to sit a bit higher on voltage indicating higher fuel trim and the B1S2 seems to vary slightly more than the secondary emissions side.

On bank 1 I have a bit of oil that seeped into 2 of the plug chambers from a **** valve cover gasket. I'll be replacing the gasket shortly.

Likewise bank 1 has an exhaust manifold leak.

Is it possible it's simply a bad 02 sensor or is there a chance that the manifold leak is causing an improper AF mixture in which case is causing a 0420 fault code?

 

[LeesEvoX]

I constantly have this code from deleting emissions on my car.

I would start with the manifold leak. This can cause additional air to be brought into the exhaust stream, which would lean out the mixture slightly. Which would make the truck add fuel once it passes the O2 sensor. Resulting I crappy mileage.

Or, the O2 sensor is bad. Have you checked the O2 sensor?

Sent from my SM-G950U using Tapatalk

 

[Kurtis West]

I constantly have this code from deleting emissions on my car.

I would start with the manifold leak. This can cause additional air to be brought into the exhaust stream, which would lean out the mixture slightly. Which would make the truck add fuel once it passes the O2 sensor. Resulting I crappy mileage.

Or, the O2 sensor is bad. Have you checked the O2 sensor?

Sent from my SM-G950U using Tapatalk

I haven't changed out my 02 sensors but visually looking at them and going off the Live Data readings of voltage they seem to be OK.

There's a bit more wiggle on the bank 1 side that has the manifold leak.

Any idea on what the ideal cat temperature is? Both cats are reading around 952 idling at temp.

Since I've got no issues on Bank 2 I figured that its an appropriate temp.

Its one of only 2 problems I have left. The other really has me shaking my head

 

[OCDTech]

Where are your LTFTs at idle and cruise (percentage). How far positive and negative. Also on a different graph (with voltage/time) do the two upstreams switch fast? or are they lazy? The two downstreams should be close to flat, not waving.

 

[Kurtis West]

Where are your LTFTs at idle and cruise (percentage). How far positive and negative. Also on a different graph (with voltage/time) do the two upstreams switch fast? or are they lazy? The two downstreams should be close to flat, not waving.

I'll have to get back in tomorrow to view the ltfts I didn't happen to look at the time.

However voltage wise the upstreams move quick as they should but the "affected" side i never really see drop below .4 v as in going lean.

Also on the affected side there is a bit faster paced movement on downstream vs the other. I've come to understand minor variation on downstream is OK as long as its not fast paced nor jumping erratically.