Failed MOT - then passed after a few days.

[I_M_Weasel]

Just had my car MOT'd, I was expecting it to fail on emissions and it did. The garage called and said they could fix it and would have it ready for me later that day, I called back in the late afternoon and they said they'd still not quite got to the bottom of it and it would take another day. So the next day at around the same time I call the garage again and get the same - not quite fixed it yet.

They called me this afternoon and said it was good to go but all it appears to have had done are new spark plugs and an oil change - would that clean up the cars emissions? (The spark plugs have done less than 5000 mile and a little over a year old, oil changed a few months ago.)

Or did the garage have no idea of the cause and just put a tick in the box to pass the MOT?

 

[Brookert]

Just had my car MOT'd, I was expecting it to fail on emissions and it did. The garage called and said they could fix it and would have it ready for me later that day, I called back in the late afternoon and they said they'd still not quite got to the bottom of it and it would take another day. So the next day at around the same time I call the garage again and get the same - not quite fixed it yet.

They called me this afternoon and said it was good to go but all it appears to have had done are new spark plugs and an oil change - would that clean up the cars emissions? (The spark plugs have done less than 5000 mile and a little over a year old, oil changed a few months ago.)

Or did the garage have no idea of the cause and just put a tick in the box to pass the MOT?

Hard to say, can you post the emissions test sheet on here? Emissions problems can be lots of things, but spark plugs are normally on the performance side of things.

 

[apeksdiver]

What car is it?

 

[I_M_Weasel]

On its pass test it says CO 0.300 HC 200 Lambda 1.09 at 3150rpm, CO 775 at idle.

I don't have the one it failed.

2.0 Mondeo petrol 2001

 

[apeksdiver]

can't see how plugs and an oil change would cure it, how much did they charge you? Sounds like they were clutching at straws.

 

[ShakenNstirred]

sounds like a garage to avoid

 

[I_M_Weasel]

There were some other jobs done as well so I'm not sure of the labour breakdown, plugs were £28, oil 28, filter £8, total labour was £175.

I'm not convinced that if I tested it somewhere else tomorrow it would pass.

 

[SixTwoSix]

I can confirm for a fact that a spark plug change can sort out emissions to pass your MOT.

Last month my focus failed with a 5.9% CO reading, the tolerance is 0.3% IIRC, the guy told me to take it home, change the plugs and bring it back.

Bought the plugs, took it back in, instant pass.

He told me if that failed, try the lambda sensor, if that failed, it could be the catalytic converter, however he told me to do the cheapest things first.

EDIT: Just found both failed and passed MOT certificate with the emissions paper.

CO Fast Idle test: 7.15%
CO 2nd Fast Idle test: 5.16%

spark plug changed then...

CO fast Idle test: 0.20%

 

[Dr Who]

Emissions problems can be lots of things, but spark plugs are normally on the performance side of things.

"Faulty" plugs cause incomplete combustion/misfiring (hence performance issues), incomeplete combustion throws off emissions, as you have a load of extra oxygen and HC going down the exhaust pipe.

 

[Rich1988]

old/damaged plugs can certainly cause a fail yes

 

[bledd]

Who fitted the previous plugs? Where they the correct type? and correct gap?

 

[Dogbreath]

On its pass test it says CO 0.300 HC 200 Lambda 1.09 at 3150rpm, CO 775 at idle.

I don't have the one it failed.

2.0 Mondeo petrol 2001

Are you reading the sheet correctly? Those numbers happen to be the pass/fail thresholds, so it would be mighty suspicious if all three measured values just happened to land exactly on these thresholds at high idle.

Also '775' makes no sense for the CO emissions at natural idle, the limit is 0.5% for your car.

Also it should be obvious that worn spark plugs can affect emissions, why would they be a service item otherwise? However 5000 miles is an extremely short life.

 

[I_M_Weasel]

Also '775' makes no sense for the CO emissions at natural idle, the limit is 0.5% for your car.

Also it should be obvious that worn spark plugs can affect emissions, why would they be a service item otherwise? However 5000 miles is an extremely short life.

I think I've read the form wrong, should be .038, 53, 1.011.

and the 775 should be 0.01

The same garage replaced the plugs when the coil pack failed, come to think of it thats when the exhaust started to look smokey.

 

[K.C. Leblanc]

Sounds like straw clutching to me. I was under the impression that most cars did better on emissions if tested while the engine was warm. So they might have just retested it with a warm engine.

 

["andy"]

They could have done a series of things to bring emissions down or they could have plugged the probe into another car (less likely considering if you where from vosa doing a check then they would get a ban)

I'm not convinced that if I tested it somewhere else tomorrow it would pass.

Take it somewhere and ask them to check your Emissions then. takes 2 minutes

 

[BigAndy87]

take it for an "italian tune up" just before your mot time get the system up to temperature.

 

[I_M_Weasel]

They could have done a series of things to bring emissions down or they could have plugged the probe into another car (less likely considering if you where from vosa doing a check then they would get a ban)

Take it somewhere and ask them to check your Emissions then. takes 2 minutes

I'm a long standing repeat customer, so I don't think they'd worry about me being from VOSA. I'm not worried myself about the emissions, I don't think that I'm the cause of global warming but I am worried about MOT next year and paying for the same problem again.

 

[One]

They could have done a series of things to bring emissions down or they could have plugged the probe into another car (less likely considering if you where from vosa doing a check then they would get a ban)



Take it somewhere and ask them to check your Emissions then. takes 2 minutes

could have

 

[Vanilla]

On this subject i'd also heard of them spraying a can of something...erm...somewhere. i wasn't really listening to help it pass emissions.

 

[realscot]

yeah plenty of aftermarket stuff you can pour in with the fuel to help bring emissions down, mostly cat regenerator stuff. I was a bit sceptical about these till I saw with my own eyes that they really do work and can bring emissions down significantly.
Engine must be up to temp before doing the emissions test anyway, so unless its a lazy tester it won't be that.