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P0420 CEL and cruise flashing on new rebuild. with AP datalog

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Let me start by saying I just finished my YNANSB. rebuild thead can be found here.




To give you a quick summery of my car I am running Cobb AP economy tune for breakin. Cobb SF intake/box, GS TMIC, rebuilt Custom VF40 by JMP, GS uppipe, Cobb DP, 3" Magnaflow exhaust, GS crank pulley, rebuilt oem injectors, original fuel pump, original o2 sensors...


I am currently trying to figure out a new problem that has come to light. I clocked up 500 issue free miles using the cobb economy tune but then something happened.


I was driving down the highway and messing with the cruise control (accelerating then decelerating) 3-4 times over a ~1k range. I was mesmerized how hard the cruise accelerated . All of a sudden the CEL comes on the the cruise starts flashing. I quickly pulled over to check the code which was P0420 Catalyst System Efficiency Below Threshold (Bank 1). oh yeah this also occurred on 4/20, oh the irony. The car seemed to run fine so i drove to home. probably 4 miles


I thought my fidgeting with the cruise caused the CEL and limp mode. I ended up resetting the ECU (COBB economy tune) and the CEL, code and flashing cruise all went away. I guess cobb doesnt disable the P0420 code in the economy tune.


I went on a short drive and everything seemed good. the DAM worked itself up form .5 to 1 and I didn't see any abnormal feedback knock or fine knock learning.


The next day I was driving home from work. I was accelerating when I felt a loss of throttle almost like the fuel cut out. I pulled over and used the AccessPort to scan for codes but nothing came up. everything felt normal during idle and i figured my car was just in limp mode. I turned on the fuel pump duty just to see if there was any correlation. Interestingly whenever I accelerating harder and the fuel pump duty hit 100 the throttle would cut out.


Ive done a few more short drives to capture this event on the AccessPort.


I just notice today my A/F learning 1 is coming in at -8.59. This is outside the +-8 recommended range according to COBB and so this also raises concern. not sure exactly when the AF left the acceptable range but before 4/20 the A/F learning 1 never went past -7.



Ive also tested the cruise control which now works (I think this means im not in limp mode)



Also at 1 point while reproducing the thottle cut event, I swear I heard a small backfire.


I only have 1 cat which is in the downpipe so this setup might be contributing to the issues. the Cobb DP is new so its not clogged.


I have done a decent amount of research and have some things i plan to try but wanted to see if anybody has any suggestions.


I need to call/email cobb and see what they think. my breakin tune is scheduled for 1 month from now.


Things that might be causing the problem

1)o2 sensor - can a bad o2 sensor lead to the throttle cut events like im experiencing?


2)fuel pump


3)some sort of leak (vacuum or exhaust)


4)electrical something dealing with the cruise. <dont think this is the issue


If you have any other suggestions or advice it would be greatly appreciated


4.6 seconds is where the throttle cut occured, the log was taken in 3ed gear.


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Today I flashed to the Stage 2 and drove down the street, the AF Learning 1 decreased even more, now its ~-11.


Also the fuel cut issue still persist when Fuel Pump Duty hits 100


After the short drive (~.2miles) I flashed back to the Economy tune. I idled the car. during idle I watched the AF Learning 1 A drop form 2.2 to 0.1 over about 2 minutes.


As the AF learning drops the engine runs richer and fuel is being reduced to compensate. this is my understanding atleast.


Im going to plug the intake, pressurize (blow into) the bpv return hose and listen for a leak.


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