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[TheBoy]

The MAF value is about 9.1 Kg/h which is a bit low.

any sign of a vac leak, pipe not fitted on inlet, brake servo pipe ok?

I would say for a 2.2 at hot idle that 9kg/hr is the lower end of normal.

I would have thought there would be some lamda activity, even if MAF was low, and the the LT trim would move drastically from 0%.

I suspect that its not trimming because it can't see any lamda activity, thus is ignoring it.

What d'ya reckon?

[Entwood]

Contact cleaner won't work on the first film type MAFs (it does on the old hot wire ones).

Of the MAF is causing a lean mix then the lambda won't switch

I accept what you are saying ... but don't understand why so I ask in order to learn ....

Assuming "Closed Loop"

If the MAF is low, yes the initial fuel from the ECU will also be low but should still be in the correct "ratio" to what the MAF "thinks" rather than what is so the mixture is lean - understand that bit .....

....if the lambda then senses that lean mix, surely the ECU should ADD fuel to correct this - that's what closed loop is all about ?? So I would have thought a low reading MAF would give high fuel trims as the ECU/MAF/Lambda all "fight" for control ?? then the fuel mix richens and the lambda starts to work as normal ??

Once the MAF is unplugged the system reverts to a "default" setting ?? and seems to increase the fuel as the engine revs much more freely, but the lambda is still not cycling so still running lean - which would explain the loss of power I suppose but why does it stay so lean when MAF unplugged ??

Confused of North Wilts 

[Entwood]

Sorry for coming back to this one .. but a further thought (dangerous I know) has left me even more confused than the questions above did ....

If the MAF is under reading to a large(ish?) extent, and the ECU only gives MAF rated fuel .. then it runs lean .... yup .. as  said  ... got that .....

however, if my thoughts in the above post are totally wrong, the engine stays lean which accounts for the loss of power ...... why then does it fail the MOT on emissions emissions cannot be "high" on a lean running engine can they


REALLY confused of North Wilts now ... 

[Abiton]

If you go too lean, HCs can go up again due to misfiring.
Described halfway through here: http://www.autoshop101.com/forms/h55.pdf

[tommy mac]

My head hurts too    

Just a brief update: I cleaned the MAF sensor using an electronics cleaning spray (shouldn't affect any electronic components) and took the car for a run.  I thought the problem was solved as initially it seemed to run just as I would expect but once it started to warm up the hesitation was back but nothing like as bad as it had been although I'm finding it hard to be objective about this. I should point out that I did reconnect the MAF sensor for this test. Does this support the idea that it is the MAF sensor causing the problem?  A new sensor is on the way and will hopefully arrive before the weekend is out.

Thanks again to Nige for taking so much time helping sort this one out.  I'm not sure if it helps 'Confused of N. Wilts' but I wonder if this has been a simple problem of a duff sensor sending data that puts the ecu out of range and therefore making any other inputs meaningless??  This would explain the fact that the lambdas are not switching as the ecu has now 'locked' into an extreme solution.  This is probably what has been discussed (?) but I need to make sense of it in my relatively simple terms.

Once the MAF sensor has been fitted I'll post an update.  Once again....thanks for all the inputs.

Tom

[Kevin Wood]

If you go too lean, HCs can go up again due to misfiring.
Described halfway through here: http://www.autoshop101.com/forms/h55.pdf

Indeed. Plus the catalytic converter won't be active unless the mixture is centred around stoichiometric, so what little CO it does generate will go straight through.

[tommy mac]

Fitted the new MAF sensor and engine starts well . ..this is with the original lambda sensor in place, not the new one.  Seemed a little hesitant a few times and the gear box seemed less smooth than usual but after a good run everything seem perfectly normal in terms of how it runs.  The only downside is that the yellow light was back on and the same fuel trim error message (P0170) was there, as were two other error messages P0100 Air Mass Flow circuit error and one the number I forget but was the engine torque error.   Cleared the codes and had another run and the error codes have not returned.

After the engine has cooled a little I'll change the lambda sensor to the new one and see how it goes.  So it looks like the AMF sensor was the problem though I remain suspicious that the old lambda sensor may after all be duff.

This has been an interesting experience and I have learned lots.  I chose the title of the thread because having had all the weird errors generated by a bad cam sensor in the past I had decided that there is a great risk of being misled or confused by the codes and so it turned out to be.  Thanks to Entwood and the other inputs we seem to have cracked it.   I'm keeping an eye on the error codes but now I won't be so readilly intimidated by them!

What a fantastic resource this site is .

Tom

[Entwood]

Nice one

I'd be intrigued to see how the lambda is switching on both old and new sensors ... but sounds like you are getting there 

[tommy mac]

I can't check the switching but have just returned from another run with the new lambda sensor fitted and I have to say that the car is running better than before all the problems following the MOT .   No error codes - no yellow dash lights so feeling a little smug.  I'm just waiting for the engine to cool down a little then I'm off to change the oil: this will definitely be an antidote to any smugness as it's already touching on freezing here!

I'm off to Cumbria tomorrow for a couple of weeks and, if you're up to it, we could have a look at that lambda switching.

Tom

[Entwood]

I can't check the switching but have just returned from another run with the new lambda sensor fitted and I have to say that the car is running better than before all the problems following the MOT .   No error codes - no yellow dash lights so feeling a little smug.  I'm just waiting for the engine to cool down a little then I'm off to change the oil: this will definitely be an antidote to any smugness as it's already touching on freezing here!

I'm off to Cumbria tomorrow for a couple of weeks and, if you're up to it, we could have a look at that lambda switching.

Tom

Have a good run .. watch the weather its a tad cold and white up there I believe If you want the live data checked any time just call .. you have the number

I'm slowly convinced you were unfortunate to have a double fault, MAF and Lambda ..