Porsche Enthusiasts Club Forum

Hi all,

I am driving 300 miles a week in my 944 and it is going well, but it seems fuelling is not too good. I wonder if the Air Flow meter needs an overhaul. It seems when I get out I can smell unburnt fuel.

Can anyone advise what I should do and who can overhaul these air flow meters please.

Or maybe it is something else that happens to these 2.5 engines, mileage is 112,000

cheers

Neil

Hi Neil... AFM issues normally cause hunting at idle and bogging down under load so I'm not sure that would be your issue, I'm sure someone more knowledgable will be along shortly to give further advice!

has its been previously fiddled with? Mine had which caused the symptoms your describe. Thought you must have the earliest 944 going

Hi,

I am not aware of previous fiddling, I have very little idea of 'Tuning' good or bad, but it looks pretty old and standard.

I wish I could stop the car smelling of bad fuelling. Just put a bottle of injector cleaner through it but no difference.

The Air meter is the only moving part, so thought it was that. Idling and normal driving works ok, so cannot be that.

Maybe a valve is not working properly like cold start or something similar

cheers
Neil

Its not your fuel lines leaking is it?

Are you able to get the car on an emissions tester at a friendly garage and let us know the CO (Carbon Monoxide) and HC (Hydrocarbon) readings at idle?

If it is smelling of raw fuel, you might have leaky fuel lines.

If when stood behind the car it smelly fumey and makes your eyes water you are not getting complete combustion.

Incomplete combustion should give you a high hydrocarbon figure on an emissions tester. Typical hydrocarbons for a 944 without a catalytic converter are normally between 80ppm and 200ppm at idle... Bad hydrocarbons can be anything from 300 ppm upwards.

High hydrocarbons are typically caused by poor ignition components, compression, injector spray pattern or vacuum leaks.

The combination of CO and HC readings can also tell their own story. Very low CO will often result in high hydrocarbons which are being caused by a very lean mixture.. But also high CO and HC readings can be caused by the mixture being too rich.

Ideally your CO readings should be between 1.0% and 2.0% on current UK fuels.

If they are higher than this, or lower than this, ask the garage to adjust the airflow meter bypass screw, which is located between the black cover on the airflow meter and the intake boot which goes to the throttle body, on the same face of the airflow meter as the black cover. it is recessed down by about an inch or so in a hole with an Allen head, from memory I think it is a 3mm allen key that they will need to use to adjust it... Usually screwing it in will cause an richer mixture, screwing it out will cause a leaner mixture.

If you are getting fumes in the cabin, especially if you crack a window open, or the sunroof, it is likely that the cause is the rear light clusters being poorly sealed, or a bad boot seal... This is caused by an aerodynamic effect which is almost the opposite of what many would expect, which draws air through the rear light cluster seals.

Ignition faults are often caused by bad plugs, leads, distributor cap and rotor arm... these items being in good condition and the right parts, makes a big difference to how a 944 runs.. In particular make sure the distributor cap is a Bosh item, rather than a Beru or other make, make sure the leads are Beru, and that the parts are in good condition, including the tips in the distributor cap being nice and shiney.. The plug leads should be flexible and rubbery, if they seem inflexible and plasticy, they are probably age hardened and need changing.