Sticky MAF (sorry I mean AFM!)

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Sticky MAF (sorry I mean AFM!)

Postby rollercoaster » 20 Dec 2017, 23:53

Had a random issue,
the tickover would rise for a while,
when its high even a blip on the throttle doesnt lower it,
just goes back to high tickover.
Also randomly three times its refused to start,
turning over sweet but no combustion at all.
Then it just starts and runs well.
When it was at the garage it behaved normally,
so the mechanic couldn't see what I meant.
But he told me its probably a sticky MAFF,
and to tap it with a screwdriver when its a problem.
The reasoning is if that works he will know thats the problem.
Any opinions on this please?
Its booked in for a service
and I would like to give them some tips on how to cure this.
Thanks
Last edited by rollercoaster on 09 Jan 2018, 15:29, edited 2 times in total.
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Re: Sticky MAF

Postby rollercoaster » 20 Dec 2017, 23:54

Ooops.
Its a 2.1 WBX
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Re: Sticky MAF

Postby ajsimmo » 21 Dec 2017, 00:20

Faulty Temp2 sender or wiring to it would give the high idle when warm. Non-starting will be something else, maybe an earthing problem (different for DJ and MV, which is yours?).

Have a look here...
http://wiki.club8090.co.uk/index.php/Pe ... idling_2.1

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Re: Sticky MAF

Postby Citizen Smith » 21 Dec 2017, 22:03

When my 2.1 WBX started running fast on tick over and after much faffing I tracked it down to the little micro on if I remember right the AFM which switch was not changing over in the throttle off position. A little tweak brought the tick over back down to 700 RPM at running temperature. I don't remember whether I adjusted a clamping screw or just bent the actuating arm a little bit.

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Re: Sticky MAF

Postby ajsimmo » 22 Dec 2017, 08:15

No switch on the AFM, do you mean the one underneath the throttle body? It's adjustable from above (if not seized) by undoing the clamp screw and turning the little socket screw with a long Allen key.

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Re: Sticky MAF

Postby Citizen Smith » 22 Dec 2017, 13:55

Yes sorry for that but I was so warm and cosy indoors and I was too idle to get my Bentley's from the garage :oops:
Yes found it on page 24.59. It looks like I tweaked the Throttle Valve Switch.
I promise not to be a half a job Bob in future. :)

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Re: Sticky MAF

Postby rollercoaster » 04 Jan 2018, 13:54

Thanks,
its persisting as a problem and eluding me,
not got a garage near me that understands these,
AA man "fixed" it but it wouldnt start after he left..
Its a DJ with DJ electronics,
its been very wet lately and I have been fording gently flooded areas.
My friend has a known good MAFF that I could try and swap,
but its possibly air leak or bad earth?
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Re: Sticky MAF

Postby silverbullet » 06 Jan 2018, 11:22

Just for clarity: the Digijet/Digifant efi uses an AFM (Air flow meter) with a moving vane, not a MAF (Mass Air Flow sensor) which uses solid-state technology ;)

Bad earths never help the state of play, all the injector grounding earths come together on one M6 bolt on the LH cylinder head

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Re: Sticky MAF

Postby rollercoaster » 06 Jan 2018, 12:50

Cleaned those now, replaced some vacuum pipes cleaned the idle valve..
The random non starting is less random,
its not starting!
Going in behind the rear light now..
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Re: Sticky MAF

Postby rollercoaster » 06 Jan 2018, 13:10

is good sparks but no fuel apparently as plugs are dry.
Fuel pump is delivering..
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Re: Sticky MAF

Postby ajsimmo » 07 Jan 2018, 09:42

Do you have a multimeter? With ignition on, you need to have 12V at the injectors (from a common source - the relay in the box above the coil, and the ECU switches the earth at each plug to fire them). If not, it's probably the relay, or the loom.

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Re: Sticky MAF

Postby rollercoaster » 09 Jan 2018, 15:28

I do have a multimeter and unfortunately a bit of a blind spot complex when it comes to electrics.
However after using a very bright light and having my glasses on...!
Something was obvious that everyone has missed so far:
The loom from the AFM has overheated with a tell tale melted strip down one side of the loom shroud near the filter.
The wires themselves may well be ok, conductive and insulated, but its worth mentioning.
Will look closer and try testing things
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Re: Sticky MAF (sorry I mean AFM!)

Postby rollercoaster » 09 Jan 2018, 15:32

I now have a spare AFM and ECU to try,
but am slightly worried about hooking one or other up and frying something.
They are not mine to fry!
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Re: Sticky MAF (sorry I mean AFM!)

Postby rollercoaster » 09 Jan 2018, 17:43

Dared to change the AFM and it fired once, but then nothing.
That was a known good one from a DJ.
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Re: Sticky MAF

Postby ajsimmo » 10 Jan 2018, 16:41

rollercoaster wrote:Something was obvious that everyone has missed so far:
The loom from the AFM has overheated with a tell tale melted strip down one side

How on earth did we all miss that? Apparently it was obvious... :roll:
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