Failed Mot emissions
Discussion
Hi all.
Mazda Bongo, 2002 reg. 2 Litre petrol/LPG.
Recently failed badly on mot emissions.
LPG= CO at 9.3
Lambda 0.7
Petrol= CO 9.99
Lambda 0.7
I have changed the lambda sensor, took for a retest, and am still getting the exact same emissions readings.
I have had a smoke test done, only found a tiny leak near throttle body, advised by that garage that the leak is so small it wouldn't affect anything and wouldn't even bother repairing.
Car only has an obd1 socket. Tested it and got a P1170 code, relating to the lambda sensor, but not sure if this is an old code, as cleared the faults, and hasn't appeared again...yet.
Had a new MAF sensor installed approx 2 years ago.
Service done July this year, including plugs, leads, air, fuel and oil filters, oil change, injector cleaner etc.
As it's pre 2002 and more than 5 seats its allowed to have a non cat test, allowing 3.5 on CO, but is still way above this.
Has a small leak on exhaust downstream of o2 sensor, between the sensor and cat, but advised this would show a lower CO reading on the emissions test, so should be helping to show a lower CO reading anyway.
Any advice where to go next?
Car mpg has been pretty bad, approx 10 mpg on LPG, roughly same on petrol.
Thanks in advance.
Mazda Bongo, 2002 reg. 2 Litre petrol/LPG.
Recently failed badly on mot emissions.
LPG= CO at 9.3
Lambda 0.7
Petrol= CO 9.99
Lambda 0.7
I have changed the lambda sensor, took for a retest, and am still getting the exact same emissions readings.
I have had a smoke test done, only found a tiny leak near throttle body, advised by that garage that the leak is so small it wouldn't affect anything and wouldn't even bother repairing.
Car only has an obd1 socket. Tested it and got a P1170 code, relating to the lambda sensor, but not sure if this is an old code, as cleared the faults, and hasn't appeared again...yet.
Had a new MAF sensor installed approx 2 years ago.
Service done July this year, including plugs, leads, air, fuel and oil filters, oil change, injector cleaner etc.
As it's pre 2002 and more than 5 seats its allowed to have a non cat test, allowing 3.5 on CO, but is still way above this.
Has a small leak on exhaust downstream of o2 sensor, between the sensor and cat, but advised this would show a lower CO reading on the emissions test, so should be helping to show a lower CO reading anyway.
Any advice where to go next?
Car mpg has been pretty bad, approx 10 mpg on LPG, roughly same on petrol.
Thanks in advance.
Stryda said:
Hi all.
Mazda Bongo, 2002 reg. 2 Litre petrol/LPG.
Recently failed badly on mot emissions.
LPG= CO at 9.3
Lambda 0.7
Petrol= CO 9.99
Lambda 0.7
I have changed the lambda sensor, took for a retest, and am still getting the exact same emissions readings.
I have had a smoke test done, only found a tiny leak near throttle body, advised by that garage that the leak is so small it wouldn't affect anything and wouldn't even bother repairing.
Car only has an obd1 socket. Tested it and got a P1170 code, relating to the lambda sensor, but not sure if this is an old code, as cleared the faults, and hasn't appeared again...yet.
Had a new MAF sensor installed approx 2 years ago.
Service done July this year, including plugs, leads, air, fuel and oil filters, oil change, injector cleaner etc.
As it's pre 2002 and more than 5 seats its allowed to have a non cat test, allowing 3.5 on CO, but is still way above this.
Has a small leak on exhaust downstream of o2 sensor, between the sensor and cat, but advised this would show a lower CO reading on the emissions test, so should be helping to show a lower CO reading anyway.
Any advice where to go next?
Car mpg has been pretty bad, approx 10 mpg on LPG, roughly same on petrol.
Thanks in advance.
Get this sorted.Mazda Bongo, 2002 reg. 2 Litre petrol/LPG.
Recently failed badly on mot emissions.
LPG= CO at 9.3
Lambda 0.7
Petrol= CO 9.99
Lambda 0.7
I have changed the lambda sensor, took for a retest, and am still getting the exact same emissions readings.
I have had a smoke test done, only found a tiny leak near throttle body, advised by that garage that the leak is so small it wouldn't affect anything and wouldn't even bother repairing.
Car only has an obd1 socket. Tested it and got a P1170 code, relating to the lambda sensor, but not sure if this is an old code, as cleared the faults, and hasn't appeared again...yet.
Had a new MAF sensor installed approx 2 years ago.
Service done July this year, including plugs, leads, air, fuel and oil filters, oil change, injector cleaner etc.
As it's pre 2002 and more than 5 seats its allowed to have a non cat test, allowing 3.5 on CO, but is still way above this.
Has a small leak on exhaust downstream of o2 sensor, between the sensor and cat, but advised this would show a lower CO reading on the emissions test, so should be helping to show a lower CO reading anyway.
Any advice where to go next?
Car mpg has been pretty bad, approx 10 mpg on LPG, roughly same on petrol.
Thanks in advance.
And a hole in the exhaust won't help.
. I have a feeling the poor mileage is linked to the low lambda reading and the overfuelling. This is what I'm trying to work out. Guessing it's running in constant open loop for some reason.The symptoms all suggest it's running very rich so you need to figure out why.
It could be because the ECU is deliberately overfuelling because it thinks the engine is cold. And maybe it actually is.So check whether the engine comes up to temperature and the ECU sees that temperature correctly, and whether the ECU ever goes into closed loop.
It could be because there's a mechanical fault such as excessive fuel pressure, although it seems a bit unlikely for that to have affected both fuel systems.
It could be because the ECU is deliberately overfuelling because it thinks the engine is cold. And maybe it actually is.So check whether the engine comes up to temperature and the ECU sees that temperature correctly, and whether the ECU ever goes into closed loop.
It could be because there's a mechanical fault such as excessive fuel pressure, although it seems a bit unlikely for that to have affected both fuel systems.
ECU coolant temp sensor or wiring associated with it likely. Note that it uses a second sensor for the gauge so even if it shows normal temp on the gauge that's not what the ECU sees. If it’s thinking the engine is clock cold it will be enriching the mixture. And you’re right, if the lambda is showing 0.7 (assuming it works) then the problem is unlikely to be an exhaust air leak of any significance.
A proper diagnostic will tell you what coolant temp the ECU is seeing.
A proper diagnostic will tell you what coolant temp the ECU is seeing.
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