problem with co emissions on a uk car

[Finnon]

my car failed its anual test recently on emissions. the co content of the exhaust fumes was too high.

on the fail sheet i have it states the co limit must be less than or equal too 3.5%

it came out at 4.43%

it passed all the other emissions tests

I dont know if you guys in the states have a simillar sort of test for your cars?

but id just like some advice on ways to get it down.

service? injector cleaner? throttle position sensor adjustment? engine timing adjustment? airflow meter? maybe check valve clearences?

this is stuff ive thought about. can anyone else add any other suggestions?

ill also add that the engine is knocky but ive been told it shouldnt effect the emissions too greatly.

and i have swapped out the air flow meter from my other car. but as far as i knew they were both working units. i did this a month or so ago. maybe longer.

also recently but not tied in with the air flow meter change over, i noticed my fuel ecconomy got significantly worse. i was getting aproxx 100 miles for £20 worth of fuel. now i get 70 miles to aproxx the same amount of fuel if im lucky.

the car has no lambda sensor. and no cat.

and last years test it passed the emissions test easily and has done only about 3000 miles since then.

all help is appreciated

regards

Paul

 

[Finnon]

also as i just read the other emissions thread there are no error codes.

and my fail sheet reads as follows

description. limits.. actual value..
co <=3.5&#37;. 4.43% fail
hc <=1200 ppm 263 ppm pass
idle speed pass
smoke level pass

sorry its difficult to read. im not sure how i can space it all out evenly. but each line should follow the top line. ie description, limits and actual value with pass or fail coming afterwards.

 

[CRE]

A knock will usually cause emissions headaches... the ECU pulls timing and adds a lot more fuel.

 

[Finnon]

A knock will usually cause emissions headaches... the ECU pulls timing and adds a lot more fuel.

Im no expert on engines. im not a machanic or anything.

when i said knocky engine i meant the bottom end is knocking. ie if i rev it to 2.5k rpm it starts to rattle.

would this cause what you describe?

 

[AJ'S 88NA]

If you are talking about rod knock, yes it can trigger the knock sensor.

 

[Finnon]

would that not trigger a fault code though?

 

[AJ'S 88NA]

It should if the sensor is working.

 

[Finnon]

but if the sensor has failed wouldnt that throw a code also? i checked the codes just before it went in and everything was normal.

 

[Finnon]

just to let you guys know i fiitted the afm off my spares car and it passed emissions at 1.99% co whereas it had been 4.5% (roughly) when it failled its emissions test. the allowed limit is 3.5%

pleased it was an easy fix