Tuning out rear O2 / lambda sensors on 2006 Corvette

[teamzr1]

In doing a compare of a pure GM calibration you obtained and your latest tune with those DTCs off
I am not thrilled in what parameters were changed and what values were used

Compare shows on right what changes are
I suggest you at least get done what is needed in scanner testrun to determine if you're ready to go get tested and check again before going that the I/M ON_BOARD tests are in a complete state

Compare shows this tables and values changed in your tune versus GM stock calibration

Name	Description
VE Initial Correction Factor	Initial value of the VE correction factor, the ratio of the MAF airmass to the VE airmass.
Power Enrich Delay RPM	PE mode is delayed if RPM is below this value.
Power Enrich EQ Ratio	This is the main table that is used to tune WOT fuel. The values in this table are Fuel/Air multipliers (or Equivalence Ratio) ie. values greater than 1 are richer, values less than one are leaner. The values relate directly to the Stoich AFR and the resulting commanded AFR is Stoich divided by this PE multiplier. Eg. if the multiplier is 1.1 then the commanded AFR will be 14.7/1.1 or 13.36.
Catalyst Over-Temp Enable	Master enable/disable for catalyst over temperature protection.
Main Spark vs. Airmass vs. RPM Open Throttle, High Octane	This is the High Octane spark advance versus RPM and Cylinder Airmass.
Main Spark vs. Airmass vs. RPM Open Throttle, Low Octane	This is the Low Octane spark advance versus RPM and Cylinder Airmass.
IAT Spark Advance Correction - Add	This table is used to modify spark advance based on inlet air temperature. It adds to the current spark advance.
IAT Spark Advance Correction 2	This table is used to modify spark advance based on inlet air temperature.
IAT Spark Advance Correction - Mult	The multiplier is used to proportionally enable or disable this feature.
ECT Spark Advance Correction - Add	This table is used to modify spark advance based on engine coolant temperature. It adds to the current spark advance.
Knock Sensor Threshold Init	Initial learned threshold for knock detection. If knock sensor exceeds this learned value then the engine is considered knocking..
Knock Sensor Threshold Min	Minimum learned threshold for knock detection. If knock sensor exceeds this learned value then the engine is considered knocking..
Master DTC List	Tampering with emissions control devices can be illegal. Please check your local laws as well as EPA rules and regulations for legal modification. Disabling emissions controls should be used on off road use only vehicles. It is illegal to modify diagnostic test results in order to pass emissions testing. FOR OFF ROAD USE ONLY!
Shift Speed vs. TPS vs. Shift - Normal	Normal Mode Shift Speeds.
Shift Speed vs. %TPS - Normal 6th	Normal Mode Shift Speeds 6th Gear.
Shift Speed vs. TPS vs. Shift - Pattern B	Pattern B Mode Shift Speeds, selector in Drive.
Shift Speed vs. %TPS vs. Shift - Pattern B 6th	Pattern B Mode Shift Speeds, selector in Drive, 6th gear.
WOT Shift Speed vs. Shift - Normal	Normal Mode WOT Shift Speeds.
WOT Shift Speed - Pattern B	Pattern B Mode WOT Shift Speed.
Base Shift Pressure 5-4	The base line pressure (main line feed pressure solenoid) during a shift.
Shift Time Input Torque Adder PD 4-2	Adds to desired shift time for 4-2 shift based on input torque and turbine RPM.
TCC Apply/Release Speed vs. TPS vs. Gear - Pattern B	Pattern B Mode TCC Apply/Release Speeds.
Tip-In TqMgt Method - Garage Shift	Torque management method for Tip-In control torque reduction on garage shifts.

After your county/state ? Is passed, then I suggest you get like one long scanner recording testrun and clean the tune up

 

[GlosterVette]

Hi JR, thanks again for all the work you've put into analysing this data. I agree with you that I'll need to get the tune refined again, and I also agree with you that I need to get more data in order to do it. I mentioned that the idle isn't as smooth as I would normally expect, and the analysis that you've done could explain it.

By the way, I love that phrase "got their tits caught in the ringer"... I'm definitely using that one myself in future! Ha ha ha.

I'm really nervous about driving the car without a valid MoT certificate (our equivalent to the smog certificate). The police are really hot on that and it pings up on the ANPR cameras (license plate reading cameras) that are in police cars. It's one of those cases of being an easy crime to solve, so the police hammer people for it!

I think that what I'm going to have to do, is take the car for the test, and see how it goes. If it passes, then that's great news and I'm clear to do longer drives, collect more data and refine that tune. If the test fails, I'll have to figure out a plan to put it right.

Thanks so much for all your help, I really appreciate it.

 

[teamzr1]

Richer the fuel trims are, the timing is a bit too low, RPMs bit low
would cause sluggish engine at idle

Might help get those onboard smog tests into a complete state at the least
Valid drivecycle is when starting engine when ECT is less than 120 F degrees and ECT gets to at least 160 F deg
You could idle in between that temp window, shut down cool engine below the 120 F deg and then idle again
doing that 2–3 times might help speed up those smog tests getting completed

But if all they do is look for the CEL being off than no need to do the above
but you need a retune for sure overall

 

[GlosterVette]

Thanks JR. I’ll tweak the fuel trims to make them richer, add a little bit of timing and set the idle to about 650 rpm instead of being about 600 rpm, and see how the car runs. Then I’ll book in the test and keep my fingers crossed!

 

[teamzr1]

Just remember when you flash the PCM
All the on-board SMOG tests are flushed out and will be back to incomplete state
and drivecycles may be needed for tests to get back to complete/passed states, but as long as CEL does not come on would be fine
You can check the status of I/M states with your scanner

 

[teamzr1]

Looking at your existing tune in PCM now as ECT come up PCM is commanding 575 RPMs when in gear
and 600 RPM in park/neutral
Up that a bit and try a bit more timing before working on fuel trims

 

[GlosterVette]

Great advice. Thank you very much

 

[teamzr1]

Great advice. Thank you very much

Just remember, you cannot do any tuning until you get a good testrun recorded and have added the PIDs I mentioned in another post

All you know now is what the fuel trim values are when idling in park with ECT up over 200 F deg with the A/C off

The engine conditions as the PCM is broken down with at least 23 fuel trim cells and your idle recording just one of those cells, idle
Could be rich there, but other areas too lean

Example recorded testrun. Cells having no values below as those conditions were not reached for that drivecycle
and as can be seen some engine conditions show fuel trims rich where others are lean so
each cell have to be treated on its own merits

 

[GlosterVette]

Thanks for the advice. I’ve booked the car in for the test, then I’ll be able to run a full set of cycles. I can also give the car a good thrash to help clear its throat!

The earliest appointment is 24th April, so let’s see how it goes.

Fingers crossed!

 

[GlosterVette]

Good news… the car passed the MoT check. I haven’t had a check engine light. I added 50 rev/min to the idle speed, but the idle is still a bit rough.

Before adjusting the fuel trims, I’m going to check for any vacuum leaks.