Monaro O2 Sensors

[Yanayaya]

Hey,

If you recall I was having problems with my Monaro a few weeks ago. The problem was rough running (that resulted in the AC

belt jumping off the pulleys and shredding an entire rib), the EML came on but never reported any codes. I used my OBDII tool

to read them even at the exact moment they happened but they never showed anything, it always came back clear.

It's important to say at this stage that I have proflow headers, wortec adjustable exhaust and decat pipes. I have spacers on

my O2 sensors post cat.

So I took the car to my local performance garage and they had a look at her, they had her for the whole day but the problem

never occurred once whilst it was there. They took her out, left her running, tried from cold but no matter what they did she

purred like a kitten without a single fault or lumpy running.

Between that garage visit and today all has been well (so 2 weeks approx). Since I can't pull any codes out they suggested I

run my OBDII tool and log data instead so I can see the values it returns. So every morning before I go to work I log my data

and stop once I arrive so it's around a 30 minute journey through some rush hour traffic.

I managed to capture two sets of data one on a good day with no problems and one on a bad day. Here are the results, both sets of results started and ended at the same time. (full results omitted for space and clarity)

Good Day

Values	Oxygen Sensor Voltage Bank 1 - Sensor 1	Oxygen Sensor Voltage Bank 1 - Sensor 1	Oxygen Sensor Short Term Fuel Trim Bank 1 - Sensor 1	Oxygen Sensor Short Term Fuel Trim Bank 1 - Sensor 1	Oxygen Sensor Voltage Bank 1 - Sensor 2	Oxygen Sensor Voltage Bank 1 - Sensor 2	Oxygen Sensor Short Term Fuel Trim Bank 2 - Sensor 1	Oxygen Sensor Short Term Fuel Trim Bank 2 - Sensor 1	Oxygen Sensor Voltage Bank 2 - Sensor 1	Oxygen Sensor Voltage Bank 2 - Sensor 1	Oxygen Sensor Voltage Bank 2 - Sensor 2	Oxygen Sensor Voltage Bank 2 - Sensor 2
Lowest	2836	0.505	2836	0	2995	0.44	3344	0	3344	0.58	3480	0.445
Highest	2836	0.505	2836	0	2995	0.44	3344	0	3344	0.58	3480	0.445

Bad Day (what the actual f....?)

Values	Oxygen Sensor Voltage Bank 1 - Sensor 1	Oxygen Sensor Voltage Bank 1 - Sensor 1	Oxygen Sensor Short Term Fuel Trim Bank 1 - Sensor 1	Oxygen Sensor Short Term Fuel Trim Bank 1 - Sensor 1	Oxygen Sensor Voltage Bank 1 - Sensor 2	Oxygen Sensor Voltage Bank 1 - Sensor 2	Oxygen Sensor Short Term Fuel Trim Bank 2 - Sensor 1	Oxygen Sensor Short Term Fuel Trim Bank 2 - Sensor 1	Oxygen Sensor Voltage Bank 2 - Sensor 1	Oxygen Sensor Voltage Bank 2 - Sensor 1	Oxygen Sensor Voltage Bank 2 - Sensor 2	Oxygen Sensor Voltage Bank 2 - Sensor 2
Lowest	1644	0.41	1644	0	1779	0.445	1893	0	1893	0.405	2024	0.44
Highest	977503	0.115	977503	50.8	977629	0.645	977734	0	977734	0.54	977874	0.705

The 'Good Day' started at set values and remained at those values for the entire journey.
The 'Bad Day' however started at their lowest values and went everwhere in between.

Has anyone seen this sort of behaviour? To be honest I know what people will say and that's when you replace your headers and exhaust you really want a remap and that IS on the cards, for now however I am just wanting to understand what's happening. Could I have faulty 02 sensors?

[Mud_]

I'm assuming there are some transcription errors in the data, and the small numbers are voltages. These don't look right - are max/min really the same? They should be ~.1V/.9V as they should constantly switch high/low if your AFR is around stoich. Being stuck around .4V just isn't realistic.

I don't understand the big numbers at all, the trims should be a few % plus or minus. If the trims are stuck at zero it sounds like you aren't entering closed loop.

Edited by Mud_ on Friday 22 January 21:21

[Mnchsv]

If you've still got O2 sensors post cats then there lies your problem because lack off cats will upset the post cat O2 sensor because it'll being going into cat protection

Delete the post cat O2 sensors

[Mud_]

Mnchsv said:

If you've still got O2 sensors post cats then there lies your problem because lack off cats will upset the post cat O2 sensor because it'll being going into cat protection

Delete the post cat O2 sensors

Agree, not worth messing around...I've never had the rear O2s, but I'm sure you're right. Turn off the rear O2s, and cat protection too if they're never going back on.

[stevieturbo]

Unfortunately highest/lowest values dont really mean much.

You'd need a proper datalog of the entire drive

[Yanayaya]

I have that didn't want to put all that in a thread. I'll upload the excel files later today

[monkfish1]

Post cat sensors cant affect the running.

[Yanayaya]

monkfish1 said:

Post cat sensors cant affect the running.

It'd be nice to hear your thoughts on this lads because of it's not the post cat o2's then I'm at a loss as to what's gone/going wrong randomly.

[j666eds]

monkfish1 said:

Post cat sensors cant affect the running.

I haven't had my post cat sensors in for over 2 years now since decatting, without them being deactivated and it runs fine! just get an error message every so often.

[Yanayaya]

Mud_ said:

I'm assuming there are some transcription errors in the data, and the small numbers are voltages. These don't look right - are max/min really the same? They should be ~.1V/.9V as they should constantly switch high/low if your AFR is around stoich. Being stuck around .4V just isn't realistic.

I don't understand the big numbers at all, the trims should be a few % plus or minus. If the trims are stuck at zero it sounds like you aren't entering closed loop.

Edited by Mud_ on Friday 22 January 21:21

I should remove the big numbers, they are timestamps. Sorry chap.