Strange issue

[avguy]

Here's the information for testing the downstream O2 sensor circuits. For the first 3 wires, you'll be measuring the resistance from the sensor connector pins to various pins on the 2 ECU connectors, which are marked 'M' and 'K'. Each of the 3 measurements should be zero ohms, or very close to it.

The dark green wire at connector position A gets tested against ECU connector pin # K53.
The light green wire at connector position B gets tested against ECU connector pin # K36.
The brown wire at connector position C gets tested against ECU connector pin # M2.

For the brown wire at connector position D, simply check for battery voltage with the key at ON.


It's really surprising to have no performance problem when there's an active flashing random misfire taking place. It might help a lot to get that P0141 eliminated so that the ECU keeps the loop closed. If you can accomplish that, the fuel trims might be a help in figuring out what's going on. With bad MPG, it suggests rich running, which would take it back to A/F ratio problems.

One other thing that comes to mind is the possibility of that O2 connector being so messed up that it's back-feeding the ECU. I've never heard of anything like that, but with electricity there's probably a way for almost anything to happen, given the right conditions.

[Z3r0x01]

It is running rich, plugs burning black and all, with the timing being off in the beginning the plugs all burnt whit which caused the same misfire and it had a very noticeable performance issue, but now it runs really good, it has lots of power, i even had 2 other people test run it while i sat shotgun doing a live data test while it was driven, first drive with downstream o2 unplugged, 2nd with both o2 unplugged, both times it was around 60-80kmh the cel started flashing with ol fault and p0300, both times the 2 guys both said "this car is fast"

[Z3r0x01]

I pulled the cat, its actually fairly new and clear, next is o2 sensors

[Z3r0x01]

Doing that o2 wiring test from plug to ecu, tested voltage on all wires first and there is voltage readings on all wires, tested the dark green wire for resistance and on 200 setting for ohms it reads 01.0-01.9

[Z3r0x01]

K 53 is 01.0-01.9ohms
K 36 is 01.9-02.1ohms
M 2 is 01.3-01.5ohms

[avguy]

Those readings confirm that the O2 connector and wiring are ok. And you previously said that you swapped the upstream and downstream O2 sensors, and the P0141 was still set. Although that would seem to confirm the sensors are ok, it would be good if you can run one more resistance check to test the O2 sensor heater circuits. The resistance between pins C and D of the O2 wire connector (the brown wires), should be around 15 ohms.

If the resistance of the sensor heater circuits turns out to be ok, I suppose you could try to swap in new sensors anyway, but I doubt they would fix the issue. Post back with whatever results you get.

[Z3r0x01]

Results from today include, the downstream o2 sensor is and was shot, put upstream o2 in place of downstream and blocked off upstream(i know stupid idea) only due to being end of the day, took for a drive and to my surprise, no p0300, so maybe 2 new o2 sensors it shall be.

[avguy]

Well that's a REALLY interesting result that you posted! The possibility that both O2 sensors are bad, but only one is setting a code makes for difficult diagnosis, to say the least. But a bad upstream O2 sensor that's sending the wrong information to the ECU, could certainly be the cause of a misfire. I still don't understand why you weren't getting at least some performance problem with a flashing random misfire, but I guess that will remain a mystery. I'll be interested to know how it's running with both sensors changed.

[Z3r0x01]

On top of this all the snow we got in the past week caused a broken exhaust at the muffler lol

[avguy]

Yep, really they're really piling it on you! Is it the factory muffler? I'd be a bit surprised if it is, because both of our Aveos had the muffler pipe rust out where it meets the mid pipe. Whatever bolts they used at the factory to connect the exhaust pipes rust away, and are impossible to anything with other than drilling them out. I crawled around on the ground messing with that on the first Aveo, but just spent an extra $90 for the other 2 pipes on the second Aveo. If the extra pipes are in your budget, it's much easier to work with all new parts and replace the whole thing (up to the cat). But of course you could also take it to a shop, where the would just cut it off and weld a new one on (or fix the break with a weld if it's not too bad). Everything is so much easier to do when it's up on a lift.