Is it normal for fuel trims to be complete opposites? Should I be looking for an exhaust leak?

LTFT B1 +18.8
STFT B1 -3.9
LTFT B2 -18.8
STFT B2 -3.9

 

Are you using HPTuner?

Does the o2 oscillate like it should?

I’d start with looking for leaks.

Cats acting up?

 

Yes. I am using HP Tuners. Someone in that forum suggested swapping the sensors. Great idea, it'll help rule them out, but they are so much fun to get out of there. Attached is the scan, more experienced eyes will see what mine do not see.

 

I would say something is up with Bank 1. At times it doesn't oscillate at all. Either you've got a cat that is on it's way to being plugged or the o2 is bad.

You can also disable LTFTs without it causing issues. You don't really need them anyway.

 

That is normal. The long term moves to get the short term to be near a plus or minus 3 percent range. Not 100% exact but that's cliff notes. Basically if you had no long term there you'd be seeing plus 15 on the short term, but your short term should be swinging up and down with the 02 sensors.. Don't get too caught up in it, they look fine.

You have 15 percent positive correction though using the numbers you posted, but again the short term should be swinging up and down, most likely it is swinging from negative 3 to positive 3.... The 15% total positive means it's adding fuel. I would check all vacuum lines and intake manifold gaskets for a leak.

Also check your maf reading at idle around 600 rpm. If you have a 5.3 you should see around 4.8 or so maybe 5.0 grams per second. That's in park, a/c off, engine fully warm, right around 550-600 rpm.

For good measure clean the maf and throttle body and clear codes and run it for a minute and recheck the fuel trims..

Also.. if the fuel trims are high like that as the engine is warming up, then get better once it's really fully hot, swap intake gaskets. Don't usually see this with GM LS motors but I do on other vehicles quite a bit.

 

I'm not on my tuning laptop, but I've seen opposite trims result from the harness being switched.

You can disconnect one and it should go to 450mv.

 

Fuel trims don't read in volts. I think you're talking about oxygen sensors.

 

I meant to disconnect an O2 sensor and it should go to 450mv. No way to disconnect a trim. :-)