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Discussion Starter · #1 ·
hi my 420gsi 2.0i k reg failed the mot on emissions this must be down to the head gasket as i have changed the cooler sensor air filter but after 30mins of running with some high revs water still comes out of the exhaust with steam not alot but defo steam what eles could this be if not head gasket it does not over heat and no oil in the water?
 

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hi my 420gsi 2.0i k reg failed the mot on emissions this must be down to the head gasket as i have changed the cooler sensor air filter but after 30mins of running with some high revs water still comes out of the exhaust with steam not alot but defo steam what eles could this be if not head gasket it does not over heat and no oil in the water?
Depends which bit of the Emission test it failed. Worn valve guides or piston rings could be two causes if the sniffing machine is picking up burnt oil.
 

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What were the emissions readings?
Have you done a compression test?

T series headgaskets don't often blow (they almost always weep oil from the front right corner though).
 

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Discussion Starter · #4 ·
rpm 2711 fast idle test
co 4.694
hc237
lambda 0.868
second fast idle test
rpm 2647
co4.220
hc 180
lambda 0.876
natural idle test
rpm 880
co2.212
 

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Wow.. just about everything is out on that one! Its just running too rich.

Change the coolant temperature sender (about £8 I think), as if it is faulty the car will richen up the mixture as if the engine was cold in the morning.

Also get a digital multimeter and probe the wires from the lambda sensor. (4 wires - two white ones which you can ignore, and a grey and a black wire. Probe between the grey and black or the grey and earth and switch the meter to a 1 volt scale. With the engine running and hot you should see the voltage switch between about 0.2 and 0.8volts about once or twice a second. If it is "switching" as it should and it still fails an emissions test then either the cat is duff or there is an exhaust leak (but it'll give different readings to the ones above).


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Ahh ok its not switching, so the emissions will never be right as the cat won't work properly unless the system is in closed loop mode (i.e the voltage on the lambda sensor is going up and down), so you can discount the cat for a little while at least.
you need to find out why the system isn't going into closed loop mode. This can be a duff sensor, an air leak somewhere and not a lot else. Clean the vacuum line to the ECU as that tends to collect oil in it.
Check all the hoses and inlet and exhasut manifold for leaks. If it has one it'll upset the engine enough to stop it going into closed loop mode.
 

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Discussion Starter · #8 ·
420 Gsi

i have a advisory notice with mot /front exhaust system has minor leak of exhaust gases mmm makes me think this maybe the problem as i have changed the lambda sensor got one from the scrap yard but isit anygood ? i have also cleaned the ecu pipe but it was clean anyway
 

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If the leak is before the lambda sensor, (i.e. at the exhaust manifold) then this will really screw up the lambda sensors readings. If it is after the sensor then it'll screw up the lambda reading given on the emissions test but it shouldn't stop the engine from behaving normally, i.e. the lambda sensor voltage should switch between low and high at least once a second.
 
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