Air Flow Meter

[dukeenfield]

Does anybody know,if you increase the the spring pressure on the flap on AFM,does it make engine richer or weaker,thanks Ken..

[dickymint]

IMHO, adjust it at your peril. (make sure you mark its original position)

[GreenV8S]

I would have thought more pressure = less movement = lower reading = less fuel. But without knowing more, I'd file it under 'not to be messed around with'.

[chunder]

GreenV8S said:

I would have thought more pressure = less movement = lower reading = less fuel. But without knowing more, I'd file it under 'not to be messed around with'.

Above is spot on - increasing spring tension = less fuel for any given air volume.

Can be adjusted but shouldn't need to be really - what symptoms have prompted the query ?

[FrenchTVR]

GreenV8s is spot on, the more tension the weaker the mixture. You need to move it approx 1/4 of a turn to make noticeable differences.

I had to spend ages with mine after a TVR main dealer had messed with it trying to cure an overfueling problem for the previous owner.
Eventually they had to fit a new ECU which was the real problem, but they never reset the air flow meter. When I bought the car it was running on 0.2% CO!!!!

As previously said, if you do have to start messing with it, mark the start point and write down how many teeth you move it and in which direction every time.
You will also really need a CO meter to be accurate in your adjustments.

[nigel_350i]

Hi,
I poked around with my airflow meter chasing an intermittent issue with poor idle/running weak. I thought about spring pressure but decided not to bother! There are several electrical checks you can do. One thing I picked up (from somewhere I can't remember) is to take the air filter of and manually "assit" the flap with a screwdriver pushing it forward. This gives you more fuel for the same airflow (ECU thinks more air so ups injector opening time) If revs rise significantly then it may be that you are runnig lean.
Hope this helps
Nigel

[wedg1e]

nigel_350i said:

Hi, I poked around with my airflow meter chasing an intermittent issue with poor idle/running weak. I thought about spring pressure but decided not to bother! There are several electrical checks you can do. One thing I picked up (from somewhere I can't remember) is to take the air filter of and manually "assit" the flap with a screwdriver pushing it forward. This gives you more fuel for the same airflow (ECU thinks more air so ups injector opening time) If revs rise significantly then it may be that you are runnig lean. Hope this helps Nigel

Fine in theory, except that when the revs rise, the airflow rises...

[dukeenfield]

I needed to ajust it,as when I took to the injection cowboy experts,they said somebody had altered it before,so they started altering the spring pressure,trying to sort out a hunting problem at the time (but couldn't do it).I have improved hunting problem by replacing induction gasket and renewing water temp sensor ect and its not running to bad now..
But when I took it for MOT the other day,the tester said the engine was running very lean about .8.
The screw for ajusting the mixture on AFM is about 2.5 turn out.thanks for help every body,

[nigel_350i]

yes I guess the revs going up increases the airflow but I think what matters is the reaction to the increased fueling provided by fooling the ecu into thinking the air flow is raised by moving the flap. If you are lean the reaction will be for the revs to rise, if you are already rich the revs won't rise much?
Once the revs have rised I agree the airflow is raised and you are back to a kind of steady state..or unsteady as with my car!

Anyway I hunted (sic) for a fault with a hunting idle, changed the inlet (valley) gasket, new throttle pot. re-sealing plenum etc. etc. And the car still does it when it feels like it

ah the joys of wedge!

[chunder]

dukeenfield said:

I needed to ajust it,as when I took to the injection cowboy experts,they said somebody had altered it before,so they started altering the spring pressure,trying to sort out a hunting problem at the time (but couldn't do it).I have improved hunting problem by replacing induction gasket and renewing water temp sensor ect and its not running to bad now.. But when I took it for MOT the other day,the tester said the engine was running very lean about .8. The screw for ajusting the mixture on AFM is about 2.5 turn out.thanks for help every body,

If it is only idle CO and lean at that then I wouldn't have thought you would need to worry about it too much. If it's also lean at higher revs then you should get this sorted asap.

Idle CO can be adjusted using the screw on the AFM (will bypass more or less air depending on setting with no effect on fuelling) or with the screw on the plenum (will bypass more or less air depending on setting but will affect the AFM and also affect fuelling slightly).

It is the screw on the plenum that is normally recommended to be set at 2.5 turns - adjusting the AFM screw should bring the CO up at idle without the need to adjust AFM spring tension.