Road Trip, now have CEL with P0420

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RoverTide

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So, I took a trip in the LR4 this weekend (about 200 miles in each direction), and on the homebound leg of the trip, I got a CEL with code P0420 - Catalyst System Efficiency Below Threshold (Bank 1). Based on my research, it could be any number of things and will be pretty tricky to ultimately diagnose the root cause. I don't really want to throw a new cat at it yet, mainly because as I look through the receipts from the previous owner, its clearly had quite a few problems with the exhaust system.

- I currently have 127k miles on the vehicle
- PO replaced drivers side exhaust camshaft, cam follower - tappett, timing chain tensioner, timing cover at 112k miles
- PO replaced both cats and 2 oxygen sensors at 107k miles
- PO replaced both cats, all oxygen sensors, and air/fuel ratio sensor at 105k miles

Currently, the gas mileage is pretty bad and there is a rattle noise in the exhaust on the drivers side... kind of makes a sound like the cat internals are rattling around. I also think I have an exhaust manifold tick, which may be the root cause. My questions for the LR brain trust:

1. Why would a vehicle eat cats like this? Constant rich condition? Exhaust manifold leak? Looking for any other ideas.
2. What PIDS should I monitor with the GAP tool to narrow down the root cause? I will check the before/aft O2 sensor voltages, but more asking about engine running conditions I should monitor?
 

djkaosone

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1. Why would a vehicle eat cats like this? Constant rich condition? Exhaust manifold leak? Looking for any other ideas.
2. What PIDS should I monitor with the GAP tool to narrow down the root cause? I will check the before/aft O2 sensor voltages, but more asking about engine running conditions I should monitor?
1. Mine turned out to be an exhaust leak between the exhaust manifold and downpipes on both sides. I used a cheap smoke tester and plugged it through the tail pipes(s) to find the leak between the up stream and down stream O2 sensors. After I fixed it, I cleared the adapations on GAP to let it relearn the fuel trims over the next few days (a week?).
2. As far as live values go, check stft1, stft2, ltft1, and ltft2 to check the live values at idle and under load (driving up hill).
 

RoverTide

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1. Mine turned out to be an exhaust leak between the exhaust manifold and downpipes on both sides. I used a cheap smoke tester and plugged it through the tail pipes(s) to find the leak between the up stream and down stream O2 sensors. After I fixed it, I cleared the adapations on GAP to let it relearn the fuel trims over the next few days (a week?).
2. As far as live values go, check stft1, stft2, ltft1, and ltft2 to check the live values at idle and under load (driving up hill).
Thanks @djkaosone. I'll give a smoke test a try. Curious, what the fix was for yours, and how did you access that area to fix it? The fuel trims seemed ok, +/- 3% for the most part, but I probably need to better educate myself on what is normal vs. abnormal and pay closer attention to any spikes in either direction.
 

RoverTide

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Or a misbehaving injector?? Are the O2 sensors oem, or cheap aftermarket?? Are the MAFs clean??
Possibly an injector... No misfires, but would I be able to tell if there is an injector problem using the GAP tool? O2 sensors are OEM, and I just cleaned the MAF's and MAP.
 

djkaosone

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You can check the injector pulse-width live values. They should all be very close together and if one is off you'll know it pretty quickly.
 

powershift

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I'd get some data logging and check your air fuel mixture. I think uburnt fuel can damage cats over time and if your mpg is down that would also lean towards a too rich mixture problem.
 

RoverTide

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Ok, I took it for a quick spin tonight to autozone and grabbed a bottle of Cataclean. After a bunch of research, I figured, what the hell... Poured it in the tank (had about 1/8th of a tank of gas), and within 2 miles, the CEL went off. Not even kidding. Drove for another 20 minutes, pretty aggressively, and CEL is still off. I also cleared the 0420 code and it did not come back within that period of driving. Seems to be the best $27 I have spent in a long time... and I will be very impressed if the CEL stays off. Not hopeful, but enjoying it while it lasts.

Regarding sensor readings, I need someone smarter than me to tell me what they think about the GAP tool screenshot I took while driving it. Mass Air Flow sensor in bank one is showing 33.4 volts... that can't be good, right? The other Mass air flow sensor is showing 1.05 volts, which seems to be more in line with the sensor voltage range I should expect. However, one of the descriptions is "Mass air flow sensor 2".. I assume that means bank 2, right?

Also, the g/hr readings fluctuated quite a bit, and definitely weren't in sync. I am not sure this screenshot is helpful for those readings as bank 1 and 2 would bounce all over the place and be similar at times and very dissimilar at times.

Edit: I also looked at the injector pulse widths, and they were all good. Nothing abnormal with any of them.

Any thoughts will be helpful.
 

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itsaguything

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Yes, Kat Kleen does work. Surprises me really. I use it before my spring time italian tune up on the xkr. It keeps away the dreaded check engine light.

Good luck on the root cause analysis. But I thought both air ducts feed into a common intake into the engine. And that the ECM did analysis across both MAFs to assist with a common fuel mixture requirements. There is no Bank 1/Bank 2 unique fuel mixture setting.
 

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