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Discussion Starter · #1 ·
Hi Guys,

As mentioned in another post of mine (clutch issues) I had my valve clearance checked the same visit I had my clutch replaced.

Some of the valves needed shims, 7 in total.
After all work done I drive home (approx. 15min. build-up area & 10min. motorway).
Next day I go to work and as soon as I am at speed on the motorway, my engine light comes on. Went back to garage, check of sensors, reset and back to home all normal.
Next day, same place; at speed on the motorway, light on.
Garage did (for free of course) extensive check. In a nutshell:
Bank 1 (left?) O2 sensor (after Cat) has disagree with A/F sensor (before Cat)
Sensor itself checks ok
Wiring checks ok
They had the exhaust after Cat taken off and with a good look could see a small burn hole in the bottom and a bigger burn hole in the 2nd layer.
Conclusion: Cat 'kaput'

I wanted to see for myself, but I need bigger tooling (I've got some cheap crap) - damn those nuts are tight!
Went to local garage for (free) readout:
P0420, bank 1 O2 sensor, engine runs lean, could be the sensor or the Cat.

Sorry for the long story, but here are my questions/queries:
-Coincidence that this happens after valve clearance check?
-If it is the Cat; replace 1 or both?
-Is there a way to unplug the O2 sensors and just keep on driving without CheckEngineLight? (looked for a connector but I see the wiring of both sensors disappear into a big cableloom)
-If it runs lean, could that hurt the engine?
-I think, and hear, that I can keep on driving this way, but can I?

Thanks in advance for any input!!
 

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-Coincidence that this happens after valve clearance check?
-If it is the Cat; replace 1 or both?
-Is there a way to unplug the O2 sensors and just keep on driving without CheckEngineLight? (looked for a connector but I see the wiring of both sensors disappear into a big cableloom)
-If it runs lean, could that hurt the engine?
-I think, and hear, that I can keep on driving this way, but can I?
Since no one's answered I'll have a go.
If your engine was running well after the valve adjustment I don't see how it could have burn out the cat and I think you would have gotten a CEL for out of spec fuel/air ratio first. Were the 7 valves too loose or too tight?
I don't know how to get around a CEL if you don't replace the cat(s). Perhaps you can find cheaper aftermarket parts?
Running "lean," well, it's not likely to be very lean just out of tolerance for emissions and a long cat life.
 

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Pull off a battery cable to reboot the ECU, let it re-learn and see if the "problem" goes away, is my suggestion.

It has worked for others. ;)
 

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Puk, at what mileage were your valves done, did you notice any change in performance, and what were the specs of the shims? Not many people have posted information about valve inspection outcomes on the 2.7, but I don't recall anyone needing so many shims.
 

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Discussion Starter · #5 ·
Thanks Kiwi!

You're saying lean won't hurt?

Haven't noticed any change....fuel consumption might even be a touch higher :mad:
Unfortunately I don't know shims where/less-more/etc, just that I haven't done it in 50.000kms (since buy) and I doubt if it has ever been done, hence the reason I had it done.
I was indeed thinking about aftermarket. The dealer has experience with cheap ones but the fault will return in a few months. Their supplier now has a cat that is Euro3 standard and that seems to help. They'll cut the old cat and weld the aftermarket in place.
(That answers Geevee as well)

@Max: you're right, that does work, but since it's a real fault it will came back after the ECU sensed the fault 3 times.

I'm still unsure what is best to do, 'cause a (or2) new cats are veeeeerry expensive!

Thanks guys!
 

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@Max: you're right, that does work, but since it's a real fault it will came back after the ECU sensed the fault 3 times.
True, unless it was the occasional fluke. :) I like to start there on the chance that it's a cheap / easy fix. Sometimes it works in your favor, but if a hard fault....yeah, re-code time.
 

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First - it's not a disagreement between the first & second O2 sensors, it the other way around - they are agreeing.

The purpose of the first O2 sensor is to determine the fuelling, the purpose of the second O2 sensor is to measure converter efficiency, if the converter is working the second O2 sensor will always report less free oxygen than the first, so if the two are returning similar readings, it triggers your P0420 converter below efficiency threshold alarm.

I don't know how the local garage came up with the "lean" diagnosis, the P0420 has nothing to do with a lean mixture, and neither does the converter - so if they are suggesting a lean mixture based on those, they are a little misguided.

It may be that they are interpreting the O2 sensor's "more free oxygen" as a lean mixture, which technically would be correct, if it was reported by the first O2 sensor (the one that determines the fuelling), but, again the P0420 is specific to the second O2 sensor, and is triggered when that sensor's readings match those of the first sensor closely.
 

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Discussion Starter · #8 ·
Thanks for your replies guys and the clarification Fordem, I agree with all

Today finally take off the exhaust and saw the hole myself, the edges look melted.

Audio equipment Rim Wheel Auto part Technology


I still haven't made up my mind; new one or aftermarket......:confused:

In my search on the internet I found several people removing the cat or smashing the inside/smashing a pipe through (all illegal...). So they're basically ignoring the Cat, but how the hell do they get rid of the fault code???? They would have only made it worse....
 
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