Last year I had a new LS1 short block installed. I never needed an emissions test then, but now I do. The car failed saying it was running 20% to lean. I checked for vacuum leaks as best I could. Replaced MAF sensor, no help. I bought a BlueDriver code reader to see live data. I’m still learning to understand it.

After warming up, STFT BANK 1 and 2 is typically less than 5%, LTFT FOR BOTH banks at idle is 16.5% to 19.5%. Increase RPM to 3500, LTFT jumps to 25%.

No error codes but, Oxygen sensor constantly reads “vehicle has not completed testing, and Catalyst reports the same thing. I think I have an issue with an upstream Oxygen sensor, but I’m not sure. While trouble shooting, I found the bolts on the left side of the intake manifold much looser than the right. I snugged them all up, not wanting to over torque them.

any thoughts?

Tom

 

With a vacuum leak your LTFT will DECREASE as RPM is increased...with a LTFT increase with RPM it’s usually a fuel delivery issue (fuel pump or filter) or MAF sensor...if you want to increase your knowledge of fuel trims here is a great YouTube video !!

 

1st to check to see if your front 02's are working properly any one with a good scanner can read your "average front 02 voltages" Ideally they should be between .400 and .500 milivolts
Do you have long tube headrs ? if so this creates a whole other senario
You will get a lean code or rich code if your LTFT's go beyond about 20% Any postive fuel trim means your engine is running LEAN and the ECM is tryng to correct it back to 14.68-1
A cold air intake normally will make the engine go lean with the stock tune but only like 10-12%
So something else is creating such a lean reading
1 Check to see what your front 02 averages are
2 check to see if you have any air intake leaks POST MAF
3 make sure your engine switches to "closed loop " after warmed past 150* coolant temp
4 an intake manifold leak is post MAF and is un metered air and could also be the issue
If it does not switch to closed loop that is a whole other issue Start your engine let it warm up to closed loop and spray Brake cleaner around all the intake manifold ports and T-Body connections IF you have a vacumm leak the engine will stumble and try to die------
if your front 02 volatges average is lower than .400 the 02's may be fouled a higher average would create a rich mixture and a negative LTFT
Finally it is rare on a stock engine to have such a positive LTFT unless there is an 02 sensor issue
You can correct the LTFT mismatch with tuning your MAF table via data logging with HP or EFILIVE and re tuning
but normally changes in the 20% range indicate another issue
With HP or EFILIVE you can "RESET" your fuel trims to start over and they will go back to "0" Sometimes they just get stuck and re setting them works But if you re set them and they go back to 20% you have an issue as i decribed above

 

Thank you!

 

Was the MAF sensor replaced with an OEM or aftermarket ??...sometimes aftermarket aren’t the best choice !!...what is your MAF reading at idle ??....4-7 grams/second is good...mine runs around 6.5.

 

Ok, I’m just posting some of my findings as I go, in case something turns out to be the smoking gun.

Came me out this morning to try some of the things suggested, let car fully warm up and sprayed brake cleaner around the intake, engine never stumbled. I checked the live data and the fuel trims were much better! LTFT was now at about 10%. Decided on a test drive, LTFT,s jumped back up.

Short tube headers and scanner says system A Closed Loop, system B Open Loop. Apparently my scanner won’t let me read O2 voltages.

Thanks!

Tom

 

6.0 to 6.5

 

Sounds like your left side 02's are working and swithching to CL but the right side is not and stuck in OL
You really need to find a way to watch your 02 voltages as I described --sounds like to me you have a fault on the right side
PS typically 02's are classified as #1 ( pre cats) and #2 (post cats) I have never heard of them classified as A or B--
Front 02's should be " sensor 1 bank 1 ( left side)
sensor 1 bank 2 ( right side
The rear 02's should be
sensor 2 bank 1 (left side)
sensor 2 bank 2 (right side)

 

1. Don't spray brake cleaner on your engine.
2. When you sprayed and got better fuel trims you probably temperarilly plugged the leak(s). Then when you drove the car the liquid got sucked in and the leaks re-appeared.
3. I'm not confident about 1 or 2 but hope it helps.