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> Afm / Maf, General Information
Uberf1end
post 20th May 2006 10:47
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I have recently noticed a minor annoyance with my QV that I would appreciate some advice on.

It is quite hard to describe exactly what it does but I will try. When I accelerate from cold, the engine fails to deliver the power I am asking for. If I let the throttle off and reapply, often it will accelerate as it should but if I keep my foot in, it labours for a bit then delivers the correct power.

It still accelerates throughout but just feels like everything in the engine is moving in slow motion or struggling through soup. It feels like fuel is not being delivered in the requisite quantity.

Once warm, it is fine.

Does this sound like classic air flow meter issues?

If so, where would I find the b**ger to give it a clean?


Also, is a MAF just an AFM for dyslexics? wink.gif
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F355
post 20th May 2006 12:08
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It does sound like either MAF or Lambda by your description, probably more MAF. Does it ever 'judder' while driving?

AFM and MAF are the same things.

It can be found just above the battery and it looks like this with the induction piping connecting either side:

Attached File  OEM_20Bosch_20MAF_20Side.jpg ( 262.29k ) Number of downloads: 321


Clean it with circuit board cleaner or Isopropyl Alcohol avaliable at Mapins amoung other places smile.gif
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GialloEvo94
post 20th May 2006 12:11
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You probably already seen numerous post on here about disconnecting the AFM/MAF so I suggest you do this and take the car for a drive to see if it makes a difference. You will find it in the pipe that goes from the airbox on the right-hand side of the engine to the throttle body housing. The electical connection is on the top. Just simply unplug it. If this doesn't work then try the same test of driving the car with the lambda disconnected instead.

Anyway, to answer your question an AFM's / MAF's, AFM's use a fairly crude method of measuring the air flow while MAF's use a more sophisticated and precise way of measuring the air flow. They each work in the following way...

AFM (Air Flow Meter)
This just measures the flow with a kind of crude spring-loaded 'door' mechanism where the door operates a variable resistor. The value of resistance is set on the variable resistor by the amount the 'door' is open by and this resistance is used to determine the air flow.

MAF (Mass Air Flow)
This uses 2 wires, one cold and one heated. In very basic terms, the passing of air over the wires cools the hot wire and the difference in temperature between the hot and cold wire is used to determine the air flow.


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Uberf1end
post 20th May 2006 13:49
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Interesting, thanks.

It does judder a little too...So, I'll take a look.

On some of the other threads, people talk about 'not touching the wires', why so?

I'll go for AFM first but, if no joy, I take it the Lambda is tucked away atop the exhaust manifold, close to the engine?
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GialloEvo94
post 20th May 2006 14:02
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QUOTE(Uberf1end @ May 20 2006, 02:49 PM)
I'll go for AFM first but, if no joy, I take it the Lambda is tucked away atop the exhaust manifold, close to the engine?
*

The lambda connection is the 4-wire black connector on top of the intake manifold in the centre of this picture...



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Uberf1end
post 20th May 2006 14:31
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Thanks, the black one to the left of the white one? (just right of centre).
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GialloEvo94
post 20th May 2006 15:50
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QUOTE(Uberf1end @ May 20 2006, 03:31 PM)
Thanks, the black one to the left of the white one? (just right of centre).

yep smile.gif


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F355
post 20th May 2006 18:14
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GE's pic is for the later phase two (plastic top) engine. If yours is the earlier ally top engine the lambda connection is under a black cover against the bulkhead, but it has exactly the same connector.

Don't touch the wires on the MAF because you can get grease on them from your finger which can damage them further smile.gif
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Uberf1end
post 21st May 2006 09:14
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Thanks.

I can't believe I am having to post this but I cannot get the clips undone that attach the intake pipes either side of the AFM angry.gif

They seem a fairly simple clip together mechanism but they have a sort of channel with a sliding tab in it. They have CLIC-R (IIRC) written next to them. A glance around the engine bay demostrates that I am going to need to work the pesky little b**gers out - is there a trick to them?

I feel slightly retarded but I don't want to risk brute force as it I break anything the only chance I would have of replacing it today would be Halfrauds....
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GialloEvo94
post 21st May 2006 09:31
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QUOTE(Uberf1end @ May 21 2006, 10:14 AM)
I can't believe I am having to post this but I cannot get the clips undone that attach the intake pipes either side of the AFM  angry.gif

They seem a fairly simple clip together mechanism but they have a sort of channel with a sliding tab in it. They have CLIC-R (IIRC) written next to them. A glance around the engine bay demostrates that I am going to need to work the pesky little b**gers out - is there a trick to them?

I feel slightly retarded but I don't want to risk brute force as it I break anything the only chance I would have of replacing it today would be Halfrauds....
*

Squeeze them together with a pair of pliers then use a small flat-ended screwdriver to prise the clip open. They're also not so easy to clip together again either (especially the tiny ones) so I suggest that when putting everything back together you just replace them with some standard jubilee clips of the same diameter biggrin.gif


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F355
post 21st May 2006 12:07
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QUOTE(GialloEvo94 @ May 21 2006, 09:31 AM)
QUOTE(Uberf1end @ May 21 2006, 10:14 AM)
I can't believe I am having to post this but I cannot get the clips undone that attach the intake pipes either side of the AFM  angry.gif

They seem a fairly simple clip together mechanism but they have a sort of channel with a sliding tab in it. They have CLIC-R (IIRC) written next to them. A glance around the engine bay demostrates that I am going to need to work the pesky little b**gers out - is there a trick to them?

I feel slightly retarded but I don't want to risk brute force as it I break anything the only chance I would have of replacing it today would be Halfrauds....
*

Squeeze them together with a pair of pliers then use a small flat-ended screwdriver to prise the clip open. They're also not so easy to clip together again either (especially the tiny ones) so I suggest that when putting everything back together you just replace them with some standard jubilee clips of the same diameter biggrin.gif
*



This is where buying the proper tool or modifying a pair of pliers saves you a few hours tongue.gif and the cost of new jubilee clips.

I suppose you are replacing itcompletly though? Youdon't need to remove it to clean the element. Just unscrew it from the top and it comes out.
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Uberf1end
post 21st May 2006 18:13
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Right, I've had the AFM out, sprayed it all over with Halfords Electrical Contact Cleaner and given it a rub with cotton buds. No dirt or grease appeared to come off it and it looked in good nick so I put it back and went for a drive.

This is where it got interesting - the problem (sluggish acceleration and a 'labouring' feeling) was even more noticeable than usual. So, I pulled over and disconnected the AFM...she then ran really sweetly. That's it I thought, it must be bu**ered.

So I pulled over and plugged it back in...the problem didn't return. So, I am thinking that the problem only seems to exist when cold (once I had run it with the meter disconnected, it was nice and warm by the time I plugged it back in).

Thinking back to my first test yesterday, I disconnected the meter and drove it from cold and it was fine.

So, it is likely that the AFM could have difficulty ONLY when the car is cold?

Also, is it likely that the car feeling so good is simply a result of it running rich - am I going to be disappointed with a new AFM?

It was so sweet with the meter unplugged that I am almost resolved to buy a new one anyway but I would like to be sure first!





As for those clips...ridiculous creations, I intend to replace all of them with jubilees ASAP.
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GialloEvo94
post 21st May 2006 18:37
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When you plugged the MAF back in did you switch the engine off first or do it with the engine running? Regardless though, if she did run fine both cold and hot with the MAF disconnected then it is definately the MAF which is the cause of your problem.

I believe the reason for those ridiculous clips is not just to make life difficult for us DIYers but more for the reason that they only have one 'closed' setting so when clipped up they put the correct amount of pressure on the joint as they can't be overtighted (unlike jubilee clips which can) blink.gif


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hazeyblue
post 21st May 2006 18:46
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The temp sender unit could be the culprit... mine has just been changed due to lumpy running.
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Uberf1end
post 21st May 2006 21:18
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Engine was off each time I plugged/unplugged.

The more I read, the more I become convinced it is the MAF.

I am going to do some further tests and give it another good clean (I cleaned it in situ so I'll be a bit more thorough next time) before I shell out 120 for another.

However, for future reference, am I right to assume that any garage with a decent diagnostics machine could spot whether the MAF, the lambda or the temperature sender are faulty?
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GialloEvo94
post 21st May 2006 21:54
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I believe the MAF only shows up as a fault on the diagnostics tester if it has failed completely, not if it is still working (even if so badly). Not sure about the other sensors...maybe the same? unsure.gif The ECU usually logs a fault on a sensor if it detects an open circuit on that sensor (i.e. disconnected) or the resistance on that sensor falls outside the expected tolerance range (failed or failing sensor).


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hazeyblue
post 21st May 2006 22:11
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QUOTE(Uberf1end @ May 21 2006, 09:18 PM)
However, for future reference, am I right to assume that any garage with a decent diagnostics machine could spot whether the MAF, the lambda or the temperature sender are faulty?
*

Lambda and Temp Sender will show up faults on the diagnostic - it's how I knew mine were kaput. However, not too sure about the MAF.

I will be speaking to my Alfa indi garage tomorrow - I will ask about the MAF...
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Dodger
post 22nd May 2006 08:26
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QUOTE(hazeyblue @ May 21 2006, 06:46 PM)
The temp sender unit could be the culprit... mine has just been changed due to lumpy running.
*


I would be thinking about changing the temp sender too. They are about 12 and are 5 minute change. It sounds like your car might not be using the cold setting and only using the hot mixture causing problems.


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paulcanning69
post 22nd May 2006 08:39
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have you got a alloy or plastic top engine
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Cruiser
post 23rd May 2006 08:29
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I have been looking at the same things, with regard to removig the MAF there seem to be a couple of alan key bolts, but with an upright piece preventing the use of a regular key to remove them. Is this a special tool job too? if so, where can they be bought from?

If I were to just unplug the Lamda, would that be a resonable diagnostic test? local mechanic mate of mine reckons that a lamda is likely to cause rough running/jerkyness, the MAF will cause sluggish, gutless performance.

Ed

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