29 replies to this topic

[Mrs Emma]

...Well amongst other things!!

First post - so please be kind! My 94 Sprite (Carb) failed yesterday on the Lambda readings - CO etc were well under the thresholds. The test performed was a closed loop test ( I thought that this model had an open loop system as it has a carb?? Obviously has no Lambda sensor either)

Testing chappie seemed a bit bemused as to the guidelines for testing cars with a carburettor and a catalytic converter, and VOSA were equally of little use. Advice given so far is that I will need a new cat - would like to avoid that obviously!

Hope someone can help!!

[Rosslin Racing]

you have a carb model with a cat ? then you have a tube thing and not electric sensor. whats the guy on?
I do recomend an oil change that will help.

Edited by Rosslin Racing, 05 August 2008 - 05:29 PM.

[Rented]

i know its a pain but can you type up the exact readings they gave you on the print out they would of returned with the MOT failure record )seperate sheet )

[taffy1967]

I've heard it said that there's an addendum at the back of the MOT Testers Handbook that clearly states that regardless of age, any Mini fitted with a carburettor need not be tested for a catalytic converter?

So tell him to look at the back of his book.

[Bungle]

could you tell us where you are and someone might be able to point you in the direction of a mini friendly MOT garage

[Rhyd]

"Location: North Yorkshire"

[Mrs Emma]

Thanks for all the replies! I shall be returning to the garage with a bit more ammunition now!

i know its a pain but can you type up the exact readings they gave you on the print out they would of returned with the MOT failure record )seperate sheet )

Fast idle test
CO 0.03% (pass)
HC 0014ppm (pass)
Lambda 1.198 (fail)

2nd Fast idle test
CO 0.04% (pass)
HC 0 023ppm (pass)
Lambda 1.217 (fail)

Natural Idle test
CO 0.05% (pass)


Thanks all - will look in again tomorrow to check out any further advice.

[Rhyd]

Bit late as you're not looking again before going to the garage, but...

The CO and HC levels look incredibly low - the limits are around 10 times higher than you've recorded. That's caused by the mixture being too weak, which also causes a high Lambda reading. I'd get the mixture adjusted before replacing the cat.

I deliberately weaken my mixture before an MoT as I don't need a lambda test, last time the tester made a point of coming to see me when I collected the car just to tell me it was low - "it's passed the test fine, but that's probably why it's a bit flat". Nice when the tester actually knows what he's testing!

[998dave]

Car is running very lean, lambda should be about 0.9 - 1.0.

Lambda is a measure of the air fuel ratio. at lambda = 1 you have a stoichiometric mixture, meaning that you have exaclt ythe right amount of air to burn the fuel, no more, no less. This is in theory ideal, but only if everything is perfectly mixed, means no unburnt HC's (fuel), in the exhaust.

In practice, lambda of about 0.9 is better on most carb cars, without catalysts, as it gives more power and better running, although a small amount of unburnt HC's end up in the exhaust, there's reasons for this in the combustion cycles that take too many diagrams to explain.

Essentially, your cr could do with a tune, a rolling road would probably do this in about an hour, costing £70 or 80, which seems expensive, but will give better fuel economy, power, torque, and get you through your MOT, all good there then.

I don't know what the thing about mini's with carbs, if it fails, then I'm afraid that's not the MOT stations fault, as the emissions requirements are set through legislation.

Oh, incidentally, on a cat car you have to have lambda set to close to 1 otherwise you poison the catalyst with unburnt HC's, or NOx.


Edited to take into accoune Mini_Kel's confirming there are 1994 carb mini's, thanks

Edited by 998dave, 06 August 2008 - 10:08 AM.

[mini_kel]

Dave998, There are definately 1994 mini`s that are carb models with cat`s! I had one

mrs_emma, U need to find a mini friendly gararge for next year!

[998dave]

Dave998, There are definately 1994 mini`s that are carb models with cat`s! I had one

mrs_emma, U need to find a mini friendly gararge for next year!

Fair enough, in this case, I suggest setting up with CO meter, and on rolling road for reasons given previously.

[Mrs Emma]

Cheers all - I think I have a much better idea of the lambda reading now! Will be going to the garage this aft in the vain hope of them finding a magic addendum in the MOT handbook about minis with carbs and cats.

Re mini friendly testing stations - I'm in the Skipton-ish area of N Yorks so if anyone knows a good one for next year...!

[mk3 Cooper S]

Dave998, There are definately 1994 mini`s that are carb models with cat`s! I had one

mrs_emma, U need to find a mini friendly gararge for next year!

Fair enough, in this case, I suggest setting up with CO meter, and on rolling road for reasons given previously.

Static CO adjustment is good enough for the MOT.

[benb12]

I was in Skipton last week!

Sorry for being so unhelpful, but I couldn't help myself.

On a more helpful and repetitive note, you need a more Mini friendly garage!

[Rented]

The CO and HC levels look incredibly low - the limits are around 10 times higher than you've recorded. That's caused by the mixture being too weak, which also causes a high Lambda reading. I'd get the mixture adjusted before replacing the cat.

I deliberately weaken my mixture before an MoT as I don't need a lambda test, last time the tester made a point of coming to see me when I collected the car just to tell me it was low - "it's passed the test fine, but that's probably why it's a bit flat". Nice when the tester actually knows what he's testing!

took the words outa my mouth

Always good to see emissions test results as they can tell the story of the problem straight in , by the sounds of the garage they have little experience with mini's .

our MOT testing stations are kind enougth to adjust the mixtures if needed on the test ( as will many garages i am sure ) and just have a talk on the side about what was done and as above , the reason why .

just an idea - make a section listing mini freindly garages in areas over the UK and contact information for members to use as reference ?