Emission issue

[kachel 5]

Hi all, my D6b engine gives more than 3% CO. My first guess is that it's running very rich because there is quite a petrol smell from the exhaust when the engine is running. 

There is a screw on the airflow meter, should I screw it in or out to make the mixture better and less rich? 

[PhilNW 44]

Think that screw only makes minor adjustments at tick over if you can smell petrol that probably points something else like AFM

[kachel 5]

OK, any suggestion where to start to make the air/fuel mixture better with less fuel in it? (my assumption is based on the strong fuel smell coming out the exhaust).

[jackherer 543]

Either the AFM (Air Flow Meter) as suggested above or the ECU coolant temp sensor (the blue one) are often causes of over-fuelling. It's not a matter of adjusting anything, something is faulty and needs repair or replacement.

[kachel 5]

Thanks, I'll start with replacing the afm. The coolant sensor is behind the thermostat house, correct? 

[Anthony 1,003]

23 hours ago, kachel said:

Hi all, my D6b engine gives more than 3% CO. My first guess is that it's running very rich because there is quite a petrol smell from the exhaust when the engine is running. 

There is a screw on the airflow meter, should I screw it in or out to make the mixture better and less rich? 

 

How much over 3% was the CO and what was the corresponding HC (hydrocarbon) reading?  Strong fuel smell is often the later which points to being far too rich and poor/incomplete combustion.

 

If the CO isn't much over 3% and the HC's are sensible, turn the mixture screw anti-clockwise probably three or four complete turns and see if the CO reading drops to a more sensible level (aim for around 1-1.5%).

 

If the CO is very high, HC's are high or you're seeing much worse fuel economy than usual, then you've probably bigger problems as per the posts above.

 

(I'm assuming that given that this is a D6B engine that you're running the standard Jetronic management)

[kachel 5]

Hi Anthony, the CO was 3.4% if I remember correct. I don't know about the hc. I'll check it when I go for the MOT again soon. But my first guess of turning the mixture screw on the afm is something to try at least if I understand correctly. Thanks! 

 

*edit*Yes, it runs on standard Jetronic management. 

Edited August 5, 2019 by kachel

[welshpug 1,661]

Screw out (anti clockwise) to allow more air to bypass the flap.

[kachel 5]

Today I got MOT on the car, CO was around 1%. I turned the mixture screw 4 times anti-clockwise. Me happy! Thanks a lot! 

[Anthony 1,003]

1 hour ago, kachel said:

Today I got MOT on the car, CO was around 1%. I turned the mixture screw 4 times anti-clockwise. Me happy! Thanks a lot! 

Glad you're sorted - and thanks for giving thread closure in reporting back with the resolution

[welshpug 1,661]

1% is good, they seem to run best at  around 1.5%,  too lean and you can't run quite as much ignition advance before they start pinking.

[kachel 5]

Thanks for the information Welspug, I can turn it one time clock wise and see what it does.