Emissions mot fail

[joeseth]

My car failed its mot today on emissions. It was on the hydro carbons reading, was about twice the pass limit. Is this just from running rich, because I know it does, or could it be something else?

My car has the m42 318is engine. What's the best way to stop it running rich? I've checked the blue plug and that seems ok. Haven't check at the ecu end though. Also the mot guy reckoned you mite be able to adjust the airflow meter change the mixture?

[magpie]

on the airflow meter is and adjuster screw but don't fook on with it,take it to somewhere that knows how to do it with a read out.

[joeseth]

Yeah I didn't really wanna touch it myself. It's always hard trying to sort emissions without anything to test it.

[78gizmo]

Could be lots of things, but M42's are prone to breather pipes splitting in and around the inlet manifold. This draws in air after the airflow meter, giving a lean mixture, which causes some of the fuel not to be burnt, a cause of high HC. HC (hydrocarbons) is unburnt fuel, not usually sympton of a rich mixture. Rich mixture would show too high a CO reading. What are the rest of the figures from the emmisions printout?

[joeseth]

Ahh that would make more sense as the idle is a bit lumpy, which I've heard is often a vacuum leak. Will check the others emissions reads ASAP. I've tried looking for vacuum leaks before but had no luck though

[Brianmoooore]

If the AFM adjuster hasn't been touched before, then DON'T touch it now! It was set correctly at the factory, and should never need adjustment.
Your car has a fault that's affecting the exhaust emissions, and this fault needs to be found and sorted, rather than masked by adjustments, otherwise you will forever have a car that's running not as t should be, costing you both power and fuel.
The problem with general mechanics that are used to dealing with all kinds of sh*te makes placed before them, is that they don't quite understand the quality of what's in front of them when faced with a BMW of this era. An E30 should be capable of passing MOT emissions regulations easily, getting close to the levels required of cars running cats.
High HC isn't just caused by a rich mixture - a weak mixture will send the reading off the scale equally as well. What was he CO reading, and any other gasses that you may have figures for?

[joeseth]

The cap covering the airflow adjust screw isn't there which is worrying. But I'm sure my old engine ran fine with the same one. Here are the emissions readings, they don't mean much to me without the pass limit of each.


Just remembered I had an advisory for a small gas leak between manifold and downpipe on the exhaust. Could this effect the lambda sensor reading and thus cause a problem?

[Brianmoooore]

That's not the results from an engine running rich, that's the sort of figures from one that's running lean. CO is far lower than it should be, and O2 is far higher than normal, showing that oxygen is passing right through the engine without being used up.
Are you sure you have a lambda sensor?

[joeseth]

Ahh no it doesn't have a lambda sensor your right. Ok so I should be looking for vacuum leaks etc after the airflow meter?

[78gizmo]

Yes, this! \/ \/ \/

Could be lots of things, but M42's are prone to breather pipes splitting in and around the inlet manifold. This draws in air after the airflow meter, giving a lean mixture, which causes some of the fuel not to be burnt, a cause of high HC. HC (hydrocarbons) is unburnt fuel, not usually sympton of a rich mixture. Rich mixture would show too high a CO reading. What are the rest of the figures from the emmisions printout?

Obviously would need to see the car to accuratly diagnose, but as you also have lumpy idle it sounds likely.