MOT failure, lambda too high.

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My Name: Stanleysteamer

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Model: C3 Pluriel - with or without roof
Year: 2004 (54)
Engine Size: 1.6 (16v)
Fuel Type: Petrol
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Hi,
the MOT testers told me I need to empty my tank of E10 and replace it with E5, and that will solve it!
Pluriel 1600 16v
I have been wondering if it could be a small hole in the exhaust they missed.
The O2 sensor was replaced last year.
does anyone have any ideas please?
Ta Stan
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My Name: Arfur Dent

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You could try as they suggest and run the tank down low and fill with the suggested fuel

You can check for an exhaust leak easily enough by running the engine and blocking the exhaust pipe with a rag. The hole will be easier to find, if there is one.
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My Name: Stanleysteamer

Experienced Member
Posts: 87
Joined: Wed Sep 20, 2017 9:59 pm
Model: C3 Pluriel - with or without roof
Year: 2004 (54)
Engine Size: 1.6 (16v)
Fuel Type: Petrol
Mileage: 50000
Trim Level: NA
Gearbox: SensoDrive
DPF: No
LHD or RHD: RHD (UK)
Engine name: TU5 16-valve (110 PS)
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Cheers Arfur,
As always!
Have you ever heard this stuff about E10 being likely to cause this? I sure haven't.
Everything you say makes sense and I'll go for it once the rain flipping stops!!
all the best
Stan
My Name: Stanleysteamer

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Posts: 87
Joined: Wed Sep 20, 2017 9:59 pm
Model: C3 Pluriel - with or without roof
Year: 2004 (54)
Engine Size: 1.6 (16v)
Fuel Type: Petrol
Mileage: 50000
Trim Level: NA
Gearbox: SensoDrive
DPF: No
LHD or RHD: RHD (UK)
Engine name: TU5 16-valve (110 PS)
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While we are at it, what is the easiest way to empty the fuel tank so i can maximise the amount of E5 and minimise the E10, please?
I'd syphon it if that was possible but i expect there is an anti syphon device in the filler tube.
Stan.
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My Name: Arfur Dent

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DPF: No
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The safest way would be to just use it in normal driving. Draining petrol tanks can be dangerous if not done with care. I wouldn't suggest you do it considering the risks.

E10 compatibility was introduced 2011, so if yours is older it may not be fully compatible.

The suggestion from your mechanic seems reasonable, they have probably seen this before rather than it being just a guess.
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My Name: Stanleysteamer

Experienced Member
Posts: 87
Joined: Wed Sep 20, 2017 9:59 pm
Model: C3 Pluriel - with or without roof
Year: 2004 (54)
Engine Size: 1.6 (16v)
Fuel Type: Petrol
Mileage: 50000
Trim Level: NA
Gearbox: SensoDrive
DPF: No
LHD or RHD: RHD (UK)
Engine name: TU5 16-valve (110 PS)
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Cheers Arfur!
I would agree except we do not do many miles and have half a tank to shift.
Being a kit car builder I am used to moving fuel tanks, pumps and petrol around.
Am I right in assuming the pump is an "in-tank" pump. I haven't dug out the Haynes to check.
The ideal would be a drain cock but no chance of that!
So, any other ideas? I only have two weeks to get the petrol out and it seems a bit silly to just drive it around for the sake of using up fuel!
so, so far my idea is to find the gauge sender unti take it out and syphon it through the hole, or to take the batt off, disconnect the wires to the pump, (assuming it is electric) then make a pair of connections to the pump, connect them to a batt, at a distance(!) and use the pump to pump the petrol into containers.
I await your wisdom!
Stan
My Name: Stanleysteamer

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Joined: Wed Sep 20, 2017 9:59 pm
Model: C3 Pluriel - with or without roof
Year: 2004 (54)
Engine Size: 1.6 (16v)
Fuel Type: Petrol
Mileage: 50000
Trim Level: NA
Gearbox: SensoDrive
DPF: No
LHD or RHD: RHD (UK)
Engine name: TU5 16-valve (110 PS)
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Arfur Dent wrote: Wed Nov 16, 2022 9:20 pm The safest way would be to just use it in normal driving. Draining petrol tanks can be dangerous if not done with care. I wouldn't suggest you do it considering the risks.

E10 compatibility was introduced 2011, so if yours is older it may not be fully compatible.

The suggestion from your mechanic seems reasonable, they have probably seen this before rather than it being just a guess.
Just a good update.
I had a good look today and found the exhaust blowing just slightly so a new one is now on order to be fitted Monday or Tuesday. could probably have fixed it with Gun Gum but the wife likes her car to not be bodged and nor do I!
i also bought some cat and sensor cleaner so I put that in the tank and ragged it around for 12 miles or so as per the instructions.
As the amount of E10 in the tank is now quite low I will fill it with E5 eventually and take it for retest.
thanks to yourself and all others on here for their advice. I will get back to finish the thread one way or another!
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My Name: Ozvtr

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We don't have MOT testing here where I live so I may be off base.

From what I can see, High Lambda is to do with the operation of the catalytic converter. The 'converter combines unburnt hydrocarbons into less harmful exhaust products by a catalytic process that 'burns' them. "lambda" refers to the perfect air-to-fuel ratio, or actually oxygen-to-fuel ratio. The catalytic converter is designed to run optimally at a lambda of 1. That is the theoretical perfect oxygen-to-fuel ratio. So if the air-fuel ratio is incorrect, theoretically, the 'converter is not working correctly. Now there can be a few things that might cause a high oxygen content in the exhaust.
A lean fuel mixture, remember more fuel less oxygen, less fuel more oxygen in the exhaust.
So the MOT test is concerned that the catalytic converter is not working correctly.
However, there may be mitigating circumstances here and it might not be the 'converter.
Ethanol in fuel is a 'filler'. That is; it doesn't produce much power. It's just there to 'water down' the volume of the fuel. As far as contribution to combustion goes, it may produce a lean mixture as now there is less 'fuel' passing through the combustion chamber. But, the upstream oxy sensor should pick up the lean mixture and compensate. Having said that, how sensitive is the MOT equipment? The TU5 engine uses a wide band O2 sensor which is not very accurate.
The upstream oxy sensor may be sending incorrect data to the engine ECU causing a lean mixture?
Finally, a hole in the exhaust will allow air and oxygen into the exhaust and effect lambda of the testing machine?

FYI, access to the fuel tank and fuel pump is under the rear passenger seat. There are 3 bolts at the front of the bench seat holding the seat in. Under the seat is a plastic disc about 10" across. Removing the disc gives you access to the top of the pump, the fuel hoses, the electrical connector and the pump retaining collar. The collar can be a pain to remove as tiny bits of rocks and dirt will wedge in the threads if the ring. Under the ring is a blue gasket (o-ring). This gasket expands when exposed to fuel!!! So when you come to put everything back together, the o-ring wont go back!! You have two choices, get a new O-ring or wait a few days for the old o-ring to 'dry out' and shrink.
My Name: Stanleysteamer

Experienced Member
Posts: 87
Joined: Wed Sep 20, 2017 9:59 pm
Model: C3 Pluriel - with or without roof
Year: 2004 (54)
Engine Size: 1.6 (16v)
Fuel Type: Petrol
Mileage: 50000
Trim Level: NA
Gearbox: SensoDrive
DPF: No
LHD or RHD: RHD (UK)
Engine name: TU5 16-valve (110 PS)
Has thanked: 7 times
Been thanked: 9 times

Post

Ozvtr wrote: Sat Nov 19, 2022 10:49 pm We don't have MOT testing here where I live so I may be off base.

From what I can see, High Lambda is to do with the operation of the catalytic converter. The 'converter combines unburnt hydrocarbons into less harmful exhaust products by a catalytic process that 'burns' them. "lambda" refers to the perfect air-to-fuel ratio, or actually oxygen-to-fuel ratio. The catalytic converter is designed to run optimally at a lambda of 1. That is the theoretical perfect oxygen-to-fuel ratio. So if the air-fuel ratio is incorrect, theoretically, the 'converter is not working correctly. Now there can be a few things that might cause a high oxygen content in the exhaust.
A lean fuel mixture, remember more fuel less oxygen, less fuel more oxygen in the exhaust.
So the MOT test is concerned that the catalytic converter is not working correctly.
However, there may be mitigating circumstances here and it might not be the 'converter.
Ethanol in fuel is a 'filler'. That is; it doesn't produce much power. It's just there to 'water down' the volume of the fuel. As far as contribution to combustion goes, it may produce a lean mixture as now there is less 'fuel' passing through the combustion chamber. But, the upstream oxy sensor should pick up the lean mixture and compensate. Having said that, how sensitive is the MOT equipment? The TU5 engine uses a wide band O2 sensor which is not very accurate.
The upstream oxy sensor may be sending incorrect data to the engine ECU causing a lean mixture?
Finally, a hole in the exhaust will allow air and oxygen into the exhaust and effect lambda of the testing machine?

FYI, access to the fuel tank and fuel pump is under the rear passenger seat. There are 3 bolts at the front of the bench seat holding the seat in. Under the seat is a plastic disc about 10" across. Removing the disc gives you access to the top of the pump, the fuel hoses, the electrical connector and the pump retaining collar. The collar can be a pain to remove as tiny bits of rocks and dirt will wedge in the threads if the ring. Under the ring is a blue gasket (o-ring). This gasket expands when exposed to fuel!!! So when you come to put everything back together, the o-ring wont go back!! You have two choices, get a new O-ring or wait a few days for the old o-ring to 'dry out' and shrink.
Thanks very much for this very interesting reply.
the upshot of it all is that I filled the tank with E5 petrol and I changed the centre section of the exhaust.
The end result was that on the emissions test it came up with zero for both CO and HC and the lambda was bang on the middle of the range so a pass, at tickover with an engine that had been allowed to cool for 30 minutes. so it passed and that is great!
So thanks to all those. have contributed.
Cheers!
Stan
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