Really Technical Mitsu. Question

[J2870]

K, u all know bout my wifes eclipse spending half of last year down and out. Found out it was the crankshaft position sensor, replaced it, works great. Now I have another issue. My check engine light came on and P0421 came up. It means "Warm Up Catayst Efficiency Below Threshold (Bank 1)". Certain websites say its the O2 Sensor, others say its the catalytic converter. I do have some Freeze Frame data though.

Fuel Sys 1 CL
Fuel Sys 2 CL
Calc Load(%) 31.8
ECT(deg. C) 84
STFT B1(%) 0.8
LTFT B1(%) -2.3
STFT B2(%) 2.3
LTFT B2(%) -3.9
Eng RPM 1789
Veh Speed(km/hr) 78
Spark Adv.(deg) 33.0
IAT(deg. C) 23
MAF(g/s) 15.93
TPS(%) 11.4

I'm not an expert at reading these things, and don't know what to reference them to. Any help would be appreciated.

[Cholewa]

the only thing useful on that list is the EGT, but that doesn't really tell you if your O2 sensor is messed or your cat.

Suggest: Take the cat off, beat it with a hammer, and watch the crap fall out. Reinstall, go on with life.

[bimmertech]

What does the Eclipse use for catalyst warm-up? Does it have air-injection? Most converter efficiency faults are due to a bad converter. An aging post-cat o2 sensor can set the fault and they are definitely cheaper to replace than the cat.

[TouringBubble]

I'm with Cholewa on this one ... gut the cat and space the sensor to correct the reading. Sadly, if the sensor is completely shot it won't do much good.

When it comes to cat v O2 in this case, it's basically impossible to tell which is bad without knowing what voltage the sensor requests at warmup. If the cat isn't working (not likely ... cats either work or they are stopped up and not flowing correctly) then the O2 reading will be off. If the O2 reading it off, it thinks the cat is bad and not the O2. Like Casey said, there is also the secondary air system that could be the issue.

The code reads to me like the the ECU sees that the cat is taking too long to get up to temp and it's not reading the correct O2 voltage. If the rear O2 is bad and stuck on a fixed voltage, or off by a % across the board, that could easily be the issue.

I suggest, if the car is running well (meaning no stopped up cat), go buy a spark plug anti-foul kit form the parts store and drill out one of the aluminum spacers to clear the O2 sensor. Use this between the rear O2 and the stock bung and see if the code stays off once cleared. That's the least expensive test.

What that data tells me is that the car isn't running overly rich (fuel trims within +/- 5%). Rich mixes kill cats ... that and physical damage ... and time. With the age of that car and those fuel trims, I don't see the cat being bad. It's the SAS or the O2 ... most likely the O2.

[Cholewa]

If you want to just buy one

http://www.google.com/search?source=ig&hl=en&rlz=1G1GGLQ_ENUS357&q=o2+spacer&btnG=Google+Search#q=o2+spacer&hl=en&sa=G&rlz=1G1GGLQ_ENUS357&prmd=ivnsfd&source=univ&tbs=shop:1&tbo=u&ei=21lVTZi9E83AtgeUlsyEDQ&oi=product_result_group&ct=title&resnum=1&ved=0CCgQrQQwAA&biw=1440&bih=785&fp=7516131a66805112

[zukitek]

without seeing upstream and downstream o2 scope patterns , the freezeframe data is of no use. If you can graph the upstream and downstream ...if its a bad cat then the up and down graphs will be pretty identical as far as crosscounts go. A crosscount is when the o2 volts bounce above and below 500 mv(center). Chances are the cat is bad .

[J2870]

okay, well I looked to see which one i replaced a while back and its the one before the cat. So the one after could be bad, but from all the responses im still not sure whether to replace the cat or the 02 and if i replace the 02 sensor, should i still get the spacer?

[Cholewa]

If the one pre cat is new, and you're getting the catalyst not warm enough error, I would go with cleaning the cat, and then forgetting about the CEL.