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[terry paget]

This results in the lambda reading on the MOT emission kit giving a reading of 1.00.

what did it fail on ? % CO ? what reading ?
lambda of 1.00 is within range (0.97 - 1.03)

Failed on lambda not being .97 and 1.03.

Sorry, not between those numbers. In fact it was above them, drifting about between 1.2 and 1.04.

[terry paget]

More data. Looked in my parts heap for a spare lambda sensor, 2 3-wire ones there but no 4 wires sensor. Spotted a box there labelled new 2.2 MAF. Fitted it. Now it does go into O2 closed loop, and the 1/1sensor does flip lean-rich-lean-rich, good news. However the 1/2 sensor is now stuck on rich, and the spanner light is on. Reading fault codes up comes P1555 throttle position load signal implausible with engine load.

[terry paget]

This morning I swopped MAF sensor with Ben's 2.2. That went into closed O2 loop when warming up, but came out again when hot. lambda sensor readings were all lean. I replaced the 'new' MAF sensor, lambda readings were more varied, but enginer neveer entered closed O2 loop. Despair! 

[dave the builder]

check manifold and ALL exhaust connections are not blowing when hot but be careful
a small piece of tissue ,held with long nose pliers ,like a flag can help find blows 
you did plug the lambdas in the right plugs when swapping cats etc ?
can you remember the CO and HC readings when the lambda was reading 1.2 or whatever (when it failed test ?)
i have to go out, will read through all this later , so many bits changed now 

[terry paget]

MOT passed today, phew! Thanks to all who have given advice and encouragement.
First MOT failed on emissions, serious crack in exhaust manifold likely cause. With new exhaust manifold fitted it struggled through on emisssions, but failed on handbrake, which mysteriously let me down when during the test the dynamic load caused the RH handbrake mechanism to collapse in some way. I drove it home and stripped the RH handbrake, found nothing obviously wrong and nothing broken, so I reassembled it with some less worn shoes. I had some more trouble with emissions, O2 loop was not always going into closed mode. I swopped MAF sensors twice and it changed things, but did not guarantee good behaviour. I submitted the car again anyway, and tester only retested what had failed before, so it passed.

[dave the builder]

Congrats on the pass 
Be wise to check live data again ,if post cat is rich constantly ,your cat will die
petrol and cats are expensive

[Doctor Gollum]

Good result, well earned

[BazaJT]

Congratulations on the pass,you deserve it for your perseverance if naught else Doesn't sound as though you're quite out of the woods with it yet though

[terry paget]

Congrats on the pass 
Be wise to check live data again ,if post cat is rich constantly ,your cat will die
petrol and cats are expensive

Thanks, will do. Post cat mixture seems to depend on the MAF sensor. Engine seemed to run equally well with all the sensors. I have another 2.2 in the fleet, but I cannot face it just yet.