MoT fail on O2/Lambda score

[sadlotus]

Hi all
My Jeep Cherokee, has its problems but running on gas is not one of them. In fact it runs much better on gas than on petrol.
I've owned it for a couple of years now, and in that time it's never run very well - if at all - on petrol once it's warmed up.
One LPG tuner told me the lambda senser was not working so I replaced it - the new one came up on the scanner as not working either... a broken wire I think.
Anyway - runs and drives ok... on open loop (except on petrol as I said).
Last year passed it's mot on emmisions ok. Since then I've put a manual stepper on and tuned it to run lovely.
I know there's a small crack in the exhaust manifold - will be fixing that today - the mot tester ran the revs up to overide any air leaks on the test - I don't think he discovered the manifold crack.
Made no difference.

Problem is it failed the MOT on O2 too high.
Questions:
1. I know there's a small crack in the exhaust manifold - will be fixing that today.
2. Adjusting the stepper to run lean - less gas - make the combustion burn more efficiently just for the MOT?
3. Will the short term and long term fuel trim scanner readings help me get the O2 down?
4. Suggestions?

thanks
Paul

Won't let me post a picture of the fail sheet...so


fast idle test 1 min max
CO level = 0.01% pass - 0.30
HC level = 69ppm pass - 200
Lambda = 1.15 fail 0.97 1.03


fast idle test 2 min max
CO level = 0.01% pass - 0.30
HC level = 140ppm pass - 200
Lambda = 1.38 fail 0.97 1.03


Natural idle test
CO level = 0.01% pass - 0.50

- just noticed the fuel type is down as unleaded, should it be gas? Is there a gas option on his analyser, MOT menu?

[classicswede]

Yes he needs to select LPG as the fuel type. Get him to do it again correctly

[Gilbertd]

If tested properly, with the analyser set for LPG, it would sail through. Limits when presented running on LPG are CO < 3.5%, HC < 1200ppm and no lambda check so you would have passed if he was doing his job properly.

[sadlotus]

OK. thanks for that.

I've fixed/filled a small crack on the exhaust manifold and hopefully that'll go some way to reduce the Lambda reading.
I'll also go down and see him tomorrow about the LPG/petrol setting

As for the fuel trim numbers - academic - they only send a reading to the scanner in petrol mode.

thanks again

[Gilbertd]

A vehicle should be tested on the fuel it is running on when presented for test. So if you drive in running on LPG, it is tested on LPG to the LPG limits. When he goes into the setup on the gas tester, he enters things like registration number and he then gets a screen that asks what fuel it is on and he selects LPG. Then the tester will automatically set the limits to what it should be.

Fuel trims, as you say, are academic, and with a dead lambda the petrol system will be running a default failsafe map anyway.

[Active_Lad]

A vehicle should be tested on the fuel it is running on when presented for test.

I always TELL the tester that it's presenting on LPG when I take the car in, just to be sure. I wouldn't be surprised if some testers have never even seen an LPG vehicle so when they start it up, and it doesn't immediately sound like a load of spanners in a cement mixer, they just assume it's petrol and go into "auto mode" during the test.

[Gilbertd]

it doesn't immediately sound like a load of spanners in a cement mixer

Best description of the noise made by a diesel I've heard in a long time! Am I the only sad person that has noticed one of the new Audi ads on TV? The one where it reverses up to a table with an old gramophone on it and then tips it over with the spoiler? The badge on the back of the car says TDI but the soundtrack definitely isn't a diesel......

Anyway Active-Lad where have you been recently, not living up to your name on here?

[Active_Lad]

Very un-active on here. Just been enjoying cheap smooth motoring

That said, I am suffering from a serious bout of "new car itch", but I'm struggling to come up with a solution that makes sense. The "Dash to Diesel" has limited the scope for petrol engines in proper 4x4's into the high end / performance "drug-dealer stylee". On a cost-per-mile basis, a Diesel 4x4 doesn't make financial sense because older models will cost more to run than what I have at the moment, so I need to spend upwards of £20K to get something fairly new, with the associated depreciation. Plus, it's a diesel As others have written elsewhere, as well as being unpleasant, they're expensive to run. Apart from servicing and the normal wearable components, my current car hasn't cost me anything. I'm no tecchy when it comes to cars, so I paid for a professional conversion and have reaped the benefits of that conversion. I'd do it again.

I've had my current motor for 8 years and my heart is ready for a change, yet my head keeps telling me it doesn't make sense.