14 replies to this topic

[Gizmotron]

VX failed it's MOT for high emissions, Lambda reading was 1.11 when it should be between 0.97 - 1.03. Question I have is it likely to be the Post sensor or Pre sensor? I have the Post sensor ready to fit, but i am worried if i take it back for a retest and it fails they may charge me full price again if i have to take it back a 3rd time. I have no EML on so unable to confirm which is at fault. any advise welcome as at £80 they are not cheap

[slindborg]

Thats low/lean I'd wager a cracked manifold causing an airleak. OR they simply cant measure the AFR properly... try blocking up one of the exhaust pipes when testing.

[Gizmotron]

it smell's rich and has a Larini on it if that could make any difference?

[slindborg]

what were the HC's?

[Gizmotron]

what were the HC's?

At Fast idle
1st time, HC was 5 ppm and second time 1 ppm.
1st time CO was 0.05 and second time 0.04.
both times the lambda reading was 1.11

Last year Lambda was 1.02, HC = 10, CO = 0.03

Edited by Gizmotron, 22 June 2011 - 05:01 PM.

[slindborg]

http://www.crypton.c...da_mixture.html exhaust leak cracked manifold would be prime suspect although the fitment of the Larini would be next highest on the sh** list

[Gizmotron]

http://www.crypton.c...da_mixture.html

exhaust leak cracked manifold would be prime suspect although the fitment of the Larini would be next highest on the sh** list

Thanks for the advise and link stuart. I will check for crackes in the morning, but if it is cracked this means i need to spend money on a nice 4 - 1 Tullet exhaust manifold or does anyone know of a better alternative?

If i was to replace it myself i assume i need to take the clam off?

[Gizmotron]

http://www.crypton.c...da_mixture.html

exhaust leak cracked manifold would be prime suspect although the fitment of the Larini would be next highest on the sh** list

Attempted to remove the heat shield from the manifold, but looks like i need to remove the clam as i cant undo the 3 x 10mm bolts attached to the color of the heat shield (see pic from joes below), so i moved it to one side and put my fingers around it before it got hot to feel for any leaks. If it is cracked where do they normally go as i was unable feel any leaks.

[Arno]

1st time, HC was 5 ppm and second time 1 ppm.
1st time CO was 0.05 and second time 0.04.
both times the lambda reading was 1.11

Good/low HC and CO values, high lambda (too much free oxygen in exhaust gas) => exhaust leak *after* the primary lambda sensor.

Probably not a problem with the manifold or gasket between manifold and downpipe. If that were the case then the ECU would 'see' the free oxygen and dump in a lot of fuel. You'd end up with high CO and HC (rich) *and* high Lambda. Classic indicator.

Did they plug the second exhaust pipe when doing the test? Air drawn in from the second pipe because of exhaust pulses can throw off the measurement.

Most likely culprits are flanges or other (deformed) exhaust joints allowing air into the system.

Bye, Arno.

[Ouchie]

http://www.crypton.c...da_mixture.html

exhaust leak cracked manifold would be prime suspect although the fitment of the Larini would be next highest on the sh** list

Attempted to remove the heat shield from the manifold, but looks like i need to remove the clam as i cant undo the 3 x 10mm bolts attached to the color of the heat shield (see pic from joes below), so i moved it to one side and put my fingers around it before it got hot to feel for any leaks. If it is cracked where do they normally go as i was unable feel any leaks.

You can remove and replace the manifold and heatshield with the clam on. Halfords flex head ratchet spanners fit, you however have to stretch and flex yourself and maybe sprawl over the clam. The bolts are going to be TIGHT!

The crack/split usually appears between the 2nd and 3rd primaries as the 1/2 and 3/4 pairs are cast together.

If you remove the top 2 bolts holding the heatshield on you can try bending it towards the boot then have a nosey at the manifold. *Possibly* enough room to get a look. I would bet on the tester not blocking the 1 pipe when taking the reading though.

[Andrew aka Stuwy]

1st time, HC was 5 ppm and second time 1 ppm.
1st time CO was 0.05 and second time 0.04.
both times the lambda reading was 1.11

Good/low HC and CO values, high lambda (too much free oxygen in exhaust gas) => exhaust leak *after* the primary lambda sensor.

Probably not a problem with the manifold or gasket between manifold and downpipe. If that were the case then the ECU would 'see' the free oxygen and dump in a lot of fuel. You'd end up with high CO and HC (rich) *and* high Lambda. Classic indicator.

Did they plug the second exhaust pipe when doing the test? Air drawn in from the second pipe because of exhaust pulses can throw off the measurement.

Most likely culprits are flanges or other (deformed) exhaust joints allowing air into the system.

Bye, Arno.

i assume a badly fitted back-box would also cause this problem?

Edited by Stuwy, 23 June 2011 - 07:45 PM.

[Gizmotron]

I tried to remove the heat shield (even took the color off) and still unable to get it out. I did however manage to move it enough to inspect the manifold using my telescopic mirror and a good light, but unable to see any cracks or signs of exhaust gasses leaking. I also checked the cat and exhaust and did not feel any leaks. I decided to put the original exhaust on and change the Post Lambda sensor with a genuine vauxhall one (p/n 9201421)the sensor looked a lot different to the old one which i suspect is a cheap aftermarket one. i left the car to get up to temperature and went for a spin. i then went out again after 40 mins, pulled away and was greeted with p0141 so i cleared it and it has not come back. i assume the ECU was learning and noticed a difference compared to the old one?

[Arno]

i assume a badly fitted back-box would also cause this problem?

Yup.. Any situation where outside air can be drawn into the exhaust system. Cracks in the backbox or connecting pipe also plays havoc with this.

It works a bit like a spraycan where a high-velocity gas flow (aka. the exhaust gasses) passing over a hole/crack/opening will produce a low pressure/vacuum region and draw air into the pipe.

If you stuff some rags over the exhaust opening so the pressure is raised in the system and the lambda readings go down to 1.00 then you've pretty much proven that it's a leak.

If the leak is upstream of the primarly lambda sensor (eg. cracked manifold or bad gasket between manifold and downpipe) then the giveaway usually is that the lambda is high, but also the HC and CO values. This is because the oxygen drawn into the system is detected by the ECU using it's lambda sensor and fools it into thinking the engine is running (very) lean. It responds by dumping in loads of fuel.

Of course it's *not* really running lean, so it can't burn this fuel and CO and HC go through the roof, but the fresh air getting into the system shows up as a high lamda reading at the same time with an exhaust tester.

Bye, Arno.

[Gizmotron]

PASSED
Even though there were no leaks from the manifold, cat or from the Larini I decided to play safe and put on the standard exhaust back on. The post Lambda sensor i had was for a Turbo and kept bringing up error codes P0141 and P1137 so I put the original one back on and error codes were gone.

below are results from my previous MOT tests, All tests are with a Miltek 200 Cell Cat. The emissions print out states that it was tested both times by the same person and this Garage in Guildford is used to doing these cars. so Did he not put the sensor in the exhaust far enough or is the Larini MOT Unfriendly?

Larini tested last year
CO 0.03%
HC 10 ppm
Lambda 1.02

Larini tested last week
CO 0.04%
HC 1ppm
Lambda 1.11

Standard Exhaust tested today
CO 0.07%
HC 12 ppm
Lambda 1.01

[chrisgold]

PASSED
Even though there were no leaks from the manifold, cat or from the Larini I decided to play safe and put on the standard exhaust back on. The post Lambda sensor i had was for a Turbo and kept bringing up error codes P0141 and P1137 so I put the original one back on and error codes were gone.

below are results from my previous MOT tests, All tests are with a Miltek 200 Cell Cat. The emissions print out states that it was tested both times by the same person and this Garage in Guildford is used to doing these cars. so Did he not put the sensor in the exhaust far enough or is the Larini MOT Unfriendly?

Larini tested last year
CO 0.03%
HC 10 ppm
Lambda 1.02

Larini tested last week
CO 0.04%
HC 1ppm
Lambda 1.11

Standard Exhaust tested today
CO 0.07%
HC 12 ppm
Lambda 1.01

Mine failed.... But I was stood watching, so I told him to keep trying, after revving the car for about 10min he printed out a pass.

I would read the emissions but the printout is in the car at MMG in Birmingham....

Edited by chrisgold, 27 June 2011 - 06:25 PM.