Hi all. Got a computer code problem I have no answer for, or maybe a car that wants to drive me to Colorado.
It's a good-running, non-smoking (well at least not oil, it seems...) '98 M44 with just under 140,000 miles on it (factory longblock installed at 60,000 miles due to a spun rod bearing and no time to disassemble, clean, and reassemble the original at that point in my life). Car and engine management system have just shy of 200,000 on them.
For at least the past three years or so, the computer's been lighting the Check Engine Light about every 60-120 miles with the P0420 code (Low catalytic efficiency).
Now, I'm a patient man, and I believe in troubleshooting by substitution when possible, so I've waited for things to evolve.
The code started coming up not too long (maybe a year or two - hard to remember with the car constantly screaming for 420) after I replaced my rusted-out OEM cat. with one from BavAuto.
I changed both O2 sensors. Made no difference.
That exhaust failed 55 months into a 60 month warranty, so I got a new one (for free, no hassles - I like those people). No change.
Drove that for a year or two, then changed the O2 sensors again (Bosch). No change.
Last month I happened across an extremely low mileage aftermarket replacement cat, with two like-new O2 sensors on it. I picked it up and installed it. No change.
So, I've been through three cats and three sets of O2 sensors, with no change in the computer throwing P0420 every 60-120 miles, without fail.
Any ideas where to look next? I've gotten very good at reading and resetting my codes while I drive, but it'd be even better not to have to.
Thanks,
- Eric