Help needed again for 350i

[smcquill]

Guys dont now if anyone has had these problems.....now the wedge is MOT'd back on the road, I swapped out the airflow meter with a second hand one, she idles great revs sit at 800rpm no bother...take her out on the road all warmed up, put my foot down and she slowly takes off, but is very hesitant......she will accelerate but very lumpy.......also when I come back from my 10 minute test run, she cuts out on idle sometimes when hot......any ideas...?
Cheers
Stewart

[Wedg1e]

Why did you swap the AFM, what made you think it was faulty?

[smcquill]

I swapped the AFM because it was not affecting the C02 emmission at all when using the adjustment screw.... and I was getting a blow back noise when accelerating or even just sitting revving I was getting a blow back noise from the AFM.....have been back to the garage yet to test it has an affect on the CO2 as yet......

[trevbeadle]

Have you checked the condition of the ducting between the AFM and the engine?...any air leaks will cause untold problems!

[smcquill]

It's a new ducting hose between AFM and plenum....

[superwedge]

might be the ecu,borrow one and try that,

[V8 Fettler]

smcquill said:

Guys dont now if anyone has had these problems.....now the wedge is MOT'd back on the road, I swapped out the airflow meter with a second hand one, she idles great revs sit at 800rpm no bother...take her out on the road all warmed up, put my foot down and she slowly takes off, but is very hesitant......she will accelerate but very lumpy.......also when I come back from my 10 minute test run, she cuts out on idle sometimes when hot......any ideas...?
Cheers
Stewart

Flapper? Do later Wedge EFIs have stepper motors? Air leak?

[smcquill]

Flapper wedges don't have stepper motors.....

[V8 Fettler]

smcquill said:

Flapper wedges don't have stepper motors.....

I'm aware of that, thanks. Later Wedges have 14CUX which generally has a stepper motor. Couldn't see from your first post if you had a flapper or not, but now I know!

Check for air leaks first.

[Wedg1e]

What was the replacement AFM from and does it look as though the black top cover has been prised off ang glued back on?

If someone has fiddled with the flap return spring tension it can cause all manner of strange running issues.
I wouldn't bin your old one just yet, it could be checked and repaired.

Some people swear blind that all 3.5L AFMs are created equal but I have data that suggests otherwise.

It would certainly be worthwhile trying to rule out an possible air leak around the inlet plumbing, there are quite a few places where it can get sucked in (as Mr. Maston knows!), bu993ring up the mixture.

[smcquill]

Would be keen to know a contact to recondition my old AFM, will also check for air leaks.....will be next weekend now....thanks for advice guys

[Wedg1e]

There's not much to the AFM: a flap pivoting on a pair of ball-races (that can wear and/or get gritty), the resistor matrix (the critical bit), the tension spring and an air temperature sensor.
If the flap is smooth end-to-end, catches nowhere and lands gently on its rubber bumper: no worries.
The spring can be adjusted by trial and error if you know what the voltage from the wiper should be at idle and ideally, the force on a spring balance necessary to move the flap. The voltage will get you somewhere near.
The temperature sensor rarely fails; if it does, sourcing a replacement is problematic although it's one bit you can rob from a spare unit without a problem - if you can get it out in one piece.
The resistor matrix is the fun part, I've never seen two the same.
What often happens on high-mileage units is the carbon track wears through so the wiper (attached to the moving flap) reads erratically... I think it was Adam Q who detailed a bodgification fix for this where you bend the wiper to act on a different area of the carbon track, although by definition if there's a bit of it worn through, the resistance must have changed...

If you fancy a play, and who doesn't, see here:

http://www.wedgeneering.co.uk/images/Lucas%20Airfl...

[adam quantrill]

My bodgification has always been with the throttle pot - moving the wiper slightly to get some unworn track under the contact - never tried the AFM as these don't seem to wear out as often.

On the throttle pot the exact resistance isn't a problem because it's used as a potential divider. But I've seen "trim" resistances on the AFM so I would expect the resistance value to be important.

[V8 Fettler]

Spring adjustment to the flapper should be approached with caution, fettling by small amounts with the option to return to original setting.

I didn't know there was an air temp sensor.

[Oz2]

Stewart, I had the same issue with said 350, it turned out after much looking to be an air leak in the flexible pipe from the afm to the throttle body/ plenum, and the hole was microscopic.
I replaced heaps of stuff and still it was down in performance, I ended up taking it to a race/tuning specialist, she had wires connected to everything but they found it, fixed it and what a difference.
I hope that's all it is.
Cheers
Adam

[smcquill]

Cheers Adam, I may have to take to a garage....as a last resort

[Jack Valiant]

Have a good root round the air hoses while it is running especially the AFM and plenum and the little vac hose from the fuel reg to the plenum. If you are convinced its the AFM or even ECU then try these guys … very good and quick refurb and turn around:

http://www.bba-reman.com/uk/

It will be something simple!!

Chris

[V8 Fettler]

Can duct tape hose from AFM as a precaution. Just in case.

[adam quantrill]

Run car. Spray WD40 around hoses, when the engine revs rise you've found the leak.