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[MikeDundee]

Jaime done the Tech 2 on the car today and came up with fault codes P0170 & P0173 seems to think this may be pointing towards the Lambda sensor?.......

[TheBoy]

Its actually BANK 1 fuel trim malfunction and BANK 2 fuel trim malfunction.

Cleared the codes, then a live data showed the trim values adjusting as expected.  The o2 sensors B1S1 and B2S1 were doing the normal rich/lean process. The o2 sensors B1S2 and B2S2 were reading constant Lean.

The car appears to be using quite a lot of oil, hint maybe of cam gaskets.  If oil was burning in cylinders, would this affect emmission feedback?

[Kevin Wood]

Dodgy fuel is a possibility. This is what mine barfed up when it had a dodgy tankful from Morrisons during the contaminated fuel fiasco in February. The fact that both banks are complaining makes me think it's something common to both. Fuel is a possibility, as is an air leak or metering problem, although that may well have thrown up a MAF sensor fault instead.

Could be that the Lambda sensors have been misreading due to oil consumption I guess but I think they can cope with a fair amount of oil consumption before becoming inaccurate. I'd say it's unlikely to be Lambda sensors as both are complaining. Unless something has killed them both at the same time?

Kevin

[MikeDundee]

Dodgy fuel is a possibility. This is what mine barfed up when it had a dodgy tankful from Morrisons during the contaminated fuel fiasco in February. The fact that both banks are complaining makes me think it's something common to both. Fuel is a possibility, as is an air leak or metering problem, although that may well have thrown up a MAF sensor fault instead.

Could be that the Lambda sensors have been misreading due to oil consumption I guess but I think they can cope with a fair amount of oil consumption before becoming inaccurate. I'd say it's unlikely to be Lambda sensors as both are complaining. Unless something has killed them both at the same time?

Kevin

Mmmm, I did put Morrisons fuel in it the week before last, normally always use BP, and have since used up Morrisons and back to BP again.

[MikeDundee]

All the gaskets where done on the engine e.g., sump, cams etc.. according to my mate (when I was in Thailand), I am waiting on the receipt to confirm but he is certain they were all done.

Could it be the o2 sensor playing up?

[TheBoy]

I think (but would like confirmation) that the BxS2 sensors are the ones post cat.  These were always reading lean. Not sure if this is normal.  The BxS1 sensors (pre cat ones?) were doing the Rich/lean constant cycle as expected.

[MikeDundee]

I think (but would like confirmation) that the BxS2 sensors are the ones post cat.  These were always reading lean. Not sure if this is normal.  The BxS1 sensors (pre cat ones?) were doing the Rich/lean constant cycle as expected.

Thanks Jaime, what is the difference between pre- and post

[TheBoy]

I think (but would like confirmation) that the BxS2 sensors are the ones post cat.  These were always reading lean. Not sure if this is normal.  The BxS1 sensors (pre cat ones?) were doing the Rich/lean constant cycle as expected.

Thanks Jaime, what is the difference between pre- and post

2 sensors are in exhaust between engine and cat, and the post cat ones are fitted in exhaust between cat and middle section of exhaust.

Sorry for not explaining myself properly first time.

[Kevin Wood]

I would speculate that fuel trim is controlled by the pre-cat sensors (these are the ones that are cycling, so it must be). As it was the fuel trim that caused the complaint something was causing them to correct out of the normal range. The post-cat ones are presumably there to detect when the cats are working properly so I guess they don't change state once the cats are up to temperature.

I'd expect an additional fault code if the reading from the post cats was wrong although I'm trying to think if they should be lean or rich.  :-/

Kevin

[MikeDundee]

Jaime, has already suggested checking for air leaks and vauxhall have suggested checking the air mass meter (whereabouts it that?), the mass meter?

[TheBoy]

Jaime, has already suggested checking for air leaks and vauxhall have suggested checking the air mass meter (whereabouts it that?), the mass meter?

MAF is between air filter and throttle body - in your case (V6), follow pipe from airbox (where filter is), as it goes through 90 degrees downwards, its the unit just below the 90 degree bend.

[Marks DTM Calib]

What you have to consider is that these sensors detect oxygen presence and by lean the actual reading is no oxygen...............

Its not inconceivable that the CATs act as a slight buffer for unburnt fuel and oxygen and hence everything leaving them has no oxygen (a good thing) so you could infer that always lean is the correct state.

[TheBoy]

What you have to consider is that these sensors detect oxygen presence and by lean the actual reading is no oxygen...............

Its not inconceivable that the CATs act as a slight buffer for unburnt fuel and oxygen and hence everything leaving them has no oxygen (a good thing) so you could infer that always lean is the correct state.

Yeah, wasn't sure what the post cat readings should be. Ta.

[Marks DTM Calib]

They way I see it is that when it runs slightly rich, any fuel vapour will sit on the cat and flash over when the next lean pulse appears and hence you get no O2  after the cat....

[Kevin Wood]

What you have to consider is that these sensors detect oxygen presence and by lean the actual reading is no oxygen...............
 
Its not inconceivable that the CATs act as a slight buffer for unburnt fuel and oxygen and hence everything leaving them has no oxygen (a good thing) so you could infer that always lean is the correct state.

Yes, that's right. Any unburnt hydrocarbons will react with oxygen in the cat.

However, a lean mixture implys the presence of oxygen in the exhaust. You have put less fuel in than you have oxygen to react with it so you must end up with some spare oxygen in the exhaust, surely?

You need a rich mixture to remove all the oxygen because you'll never have complete break down of all the oxygen in the air unless you have a slight excess of fuel, and this is what I couldn't get my head around.

Not sure what the after cat sensors are telling the ECU now.  :-/ Unless, it's that if there is not spare oxygen after the cat (not reading lean) then the engine needs to be leaned a little to give the cat some more oxygen wo work with.

Off to wikipedia...



Kevin