Hey folks! Picked up a GD3 (2008) Sport about a month ago. 123K miles and a bit...look to be mostly highway miles. Generally looked pretty clean, but I suspect the previous owners didn't do a lot of mechanical maintenance. Not too long after I bought it, it starting missing badly at idle (especially with A/C on). Replacing the Bosch (arrrgh!) plugs with some NGKs cleaned up the idle, but since it looked like the coil packs were original, I went ahead and put in some new Hitachi packs. It's been running flawlessly for about 500 miles. Today it decided to throw a P0420. Seems a bit early for a cat to go out, but given the rep of the coil packs, I suspect it's been missing progressively worse for the last 50K miles -- that's a lot of HC for the cat to take care of. Anywho, I was wondering if there are some methods to narrow if it's really the cat or no before I start shotgunning parts. I have the Torque app and an OBD dongle -- seems like there could be something I could do with monitoring the upstream / downstream O2 sensors. Any pointers?

Thanks!

Andy

 

Do you know this for a fact? Any misfire or fuel control problem has the potential for ruining a cat. (Including running out of gas, believe it or not.)
Suspicious. And well known for causing problems. Good move.
Could those plugs be a cause of cat failure? IDK

First find a root cause of cat failure if possible, because a poor running engine can ruin even a brand new cat in a matter of just a minute, if it runs bad enough.

Make it run perfect.
Erase codes.
See how long it takes to set the cat code again.

 

On my 07 gd, running half a can of sea foam in 4 tanks of fuel in a row did the trick, I suspect the carbon buildup in the exhaust was the culprit, from similar issues to yours.. I cleared the code each time it appeared and by the third tank the code quit coming back, then did a oil change with fresh clean full synthetic 5w-20.

I had already done plugs/coils (Hitachi) and adjusted the valves.

Cheers.

 

I agree with all that has been mentioned. Instead of Seafoam, I have run Cataclean.

 

To OP:
if possible rent scanner with life data and read the cat temperature.
The average light off temperature at which the catalytic converter begins to function ranges from 400 to 600 degrees F. The normal operating temperature can range up to 1,200 to 1,600 degrees F. (Catalytic Converter)
Dead cat is significantly colder than properly operated catalyst.
Check the fuel trims and B1S2 (O2S12) voltage at idle with ECT reading above 80 degrees C (lights off, A/C off)
- Your downstream O2 sensor should always stay at about a half a volt

 

Could you tell me or give me a link how to do this test and how to read the results?
At idle or when driving? Or at idle but after driving when converter reaches 1200F?
I have code p0420, tried cataclean - it didn't help. The car is Fit with 97k on it. Never had loss of power or misfire.
I went to clear the code and he suggested to check the rear O2-sensor - if it gets dirty I may read wrong.
He measured at idle, for O2-S11 current 0.008mA at 625F, and for O2-B1 S2 voltage 0.775V. I guess, first and second sensor (front and rear).
But he has no idea if these values are bad or good.
Please advise.

 

I am answering myself:
Ignition on > clear code > Start engine > keep 3000rpm at idle until radiator’s fan comes on>test drive > keep constant speed in range 45-75 mph for 5 min (75-120 km/h) If screen shows
passed – it is OK
-out of condition – start drive test over
-failed – replace cat. converter (after replacement another test needs be done – see book)

Observe live data for first sensor (closer to engine) – voltage should fluctuate several times per second around 450mV, from 200 to 700 – means sensor is OK
I used ML329 scanner. I was not able to find a list with all acronyms used in the device.
The catalytic convertor failure code disappeared by itself recently. The vehicle passed the test. No failure codes.
I was wondering is the first sensor still working well or it is a little bit out of range?

 

I tried Rust-Oleum Lacquer Thinner 1 Gallon, per Scotty
The check engine light is still on.

 

I never saw O2 sensor or cat cleaners to be working sorry, unless the exhaust system had a gross (oil) contamination from major engine failure