MOT emissions failure advice please..
Discussion
Lenalou said:
Hiya just an update.. I put the car into the garage today and they phoned to say there is a split in the intake manifold which is causing the high revs and altered readings in the emissions, they quoted £240 to replace it as it is a 3 hour job. They said it will be ready tomorrow.
I very much doubt this fault, if it exists, will have caused the emissions readings you got. I'm afraid I suspect you'll soon be told "we did that and it still isn't right" and the expense will continue unabated.
As someone has correctly indicated, a split in the induction system is likely to cause a weak mixture not a very rich one which is what you have. Of course there may well be a combination of faults. I did note your high idle speed reading on your test sheet so an air leak on the induction side is quite possible but I would think it more likely to be in a hose than in the manifold itself. I suggest you make sure the garage clarifies in writing exactly what component is faulty and also tell them you want any old parts back. This puts them on notice they can't just replace stuff at random at your expense.
Hi a split in an intake manifold will increase air flow in to the engine. Air and petrol are what makes the engine run correctly but they have to be balanced so much air to the correct amount of fuel.
As your car is using to much air the brain of the car (the ECU) will record this and think loads of air so it will add loads of fuel to even it out.
This will cause the failure on the emissions. I have seen it before.
Also ask the garage as the EML light is on to plug it in and code read the car as when the air/fuel mixture is to high like yours it can cause a few more problems.
One problem is it can cause a lambda sensor to fail, there is normally two of these on the car. This will put on the EML light.
Two it can cause catalytic convertor failure, to much fuel can burn out the catalytic convertor and then it is not working correct so the fumes which go through the lambda sensors have to much of the bad stuff in them and cause the EML to light up.
It is most common you will get away with just the manifold being changed but if after it is if the EML light stays on then start to look at the other two problems I have listed.
When the manifold is replaced and you get the car back I would advise going on a good 30 minute journey down a motorway or dual carriageway as this lets the car get hot and lets the ECU to correctly adjust the amounts of air/fuel mixture. Keep a check the EML light doesn't illuminate again.
Good Luck.
PS: Give it a quick service Air Filter Fuel Filter Oil and filter Change and Spark Plugs. Shouldn't cost to much.
As your car is using to much air the brain of the car (the ECU) will record this and think loads of air so it will add loads of fuel to even it out.
This will cause the failure on the emissions. I have seen it before.
Also ask the garage as the EML light is on to plug it in and code read the car as when the air/fuel mixture is to high like yours it can cause a few more problems.
One problem is it can cause a lambda sensor to fail, there is normally two of these on the car. This will put on the EML light.
Two it can cause catalytic convertor failure, to much fuel can burn out the catalytic convertor and then it is not working correct so the fumes which go through the lambda sensors have to much of the bad stuff in them and cause the EML to light up.
It is most common you will get away with just the manifold being changed but if after it is if the EML light stays on then start to look at the other two problems I have listed.
When the manifold is replaced and you get the car back I would advise going on a good 30 minute journey down a motorway or dual carriageway as this lets the car get hot and lets the ECU to correctly adjust the amounts of air/fuel mixture. Keep a check the EML light doesn't illuminate again.
Good Luck.
PS: Give it a quick service Air Filter Fuel Filter Oil and filter Change and Spark Plugs. Shouldn't cost to much.
Edited by Congletonian on Friday 16th March 13:56
Mignon said:
A couple of years ago I gave you all an equation which calculates the expected MOT lamdba value to within a couple of percent from the CO reading assuming no air leaks in the exhaust system.
https://www.pistonheads.com/gassing/topic.asp?t=15...
Lambda value = (14.5-(CO% x 0.37))/ 14.6
In this case we have CO of 2.987 which gives us a calculated lambda of 0.917 - actual 0.909 so spot on within 1% or so
Second reading 4.812 which gives us a calculated lambda of 0.871 - actual 0.857 so again about spot on.
So we can tell from this the exhaust system is good and the engine is actually burning just the air and fuel coming in from the inlet side. However, to the OP, be a bit wary of the advice you're seeing here. The lambda sensor in the car is just a feedback system to correct small errors in the ECU's base map. Even if the lambda fails there has to be something to cause the mixture to go very rich in the first place. Most likely cause is a failed coolant temperature sensor. These are easy to check and cheap to replace compared to most other things. If the ecu thinks the car is stone cold it will "put the choke on" and squirt in a lot more fuel. Now a good lambda sensor should try and correct this so it may well be that sensor has also failed but I'd first look at the coolant sensor and see what happens. The failed coolant sensor probably won't throw up a fault code so the average clueless garage mechanic won't see this on a code reader and will be unlikely to understand anything that doesn't show a code.
Your test results tell you nothing about the CAT so leave this until absolute last. Coolant sensor first, lambda sensor second, CAT only if there's still a problem.
Nice, very nice indeed. That's a cracking little tool. Thanks for sharinghttps://www.pistonheads.com/gassing/topic.asp?t=15...
Lambda value = (14.5-(CO% x 0.37))/ 14.6
In this case we have CO of 2.987 which gives us a calculated lambda of 0.917 - actual 0.909 so spot on within 1% or so
Second reading 4.812 which gives us a calculated lambda of 0.871 - actual 0.857 so again about spot on.
So we can tell from this the exhaust system is good and the engine is actually burning just the air and fuel coming in from the inlet side. However, to the OP, be a bit wary of the advice you're seeing here. The lambda sensor in the car is just a feedback system to correct small errors in the ECU's base map. Even if the lambda fails there has to be something to cause the mixture to go very rich in the first place. Most likely cause is a failed coolant temperature sensor. These are easy to check and cheap to replace compared to most other things. If the ecu thinks the car is stone cold it will "put the choke on" and squirt in a lot more fuel. Now a good lambda sensor should try and correct this so it may well be that sensor has also failed but I'd first look at the coolant sensor and see what happens. The failed coolant sensor probably won't throw up a fault code so the average clueless garage mechanic won't see this on a code reader and will be unlikely to understand anything that doesn't show a code.
Your test results tell you nothing about the CAT so leave this until absolute last. Coolant sensor first, lambda sensor second, CAT only if there's still a problem.
Mignon said:
I'm amazed.
It passed the MOT....but we didnt see the results sheet lol. Was it the same garage doing this work that MOT'd it ?And given the high base idle for the first test....surely as the owner/driver you'd have noticed that problem for some time prior to going to MOT ?
Either way, at least it's out of the way for another year
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