Positioning of the MAF's - HELP needed

[IchBautAuto]

When I bought my RS6, the PO had disconnected the MAF from the airbox, which I thought was a good idea for ease of access. After a MAF seal issue where the Apikol MAF seal hadn't adhered to the manifold, I stripped it down and found out that as well, one of the upper O Rings had been dislodged during the previous airbox installation (my fault), so I looked at installing the whole airbox arrangement this time iaw the OEM method to see how it went.

Before I did that I thought I would get some measurements just in case I was tempted to make some changes down the track to this arrangement. I removed the MAF's from the airbox and installed the bare airbox to get measurements.

Here is a rudimentary drawing of my airbox and MAF dimensions. The airbox was correctly snugged down with new locating grommets fitted. Solid and everything lined up. My outcomes:
If the MAF's are inserted into the airbox and the locating screws applied, the actual MAF will only just enter the manifold seal as shown in the drawing. The seal in fact sits below the "O Ring" groove in the manifold end of the housing, which is such a tenuous situation, it would be no wonder that air leaks would occur.

The machining in the manifold indicates that the MAF could / should be inserted 25mm into the manifold which would also provide a reasonably linear air flow, rather than the turbulence that seems likely with the stepped space currently presented with the MAF attached to the airbox.

Something here isn't right, and equally, if most people follow the book and their car is the same as mine, you would never notice the problem. The MAF are AUDI genuine and BOSCH equivalents are identical in size.

In effect, if my MAF isn't secured to the airbox, it can theoretically move up and down 17mm once everything is assembled. Not ideal in itself and the situation with the MAF installed iaw the factory arrangement is also a problem waiting to happen.

To all those out there who have had their engines apart multiple times, can anyone offer suggestions / solutions to this. I cannot see any problem with my airbox installation. All the fixing bolts line up, the locating pegs are in their grommets and fully inserted. Their isn't anywhere near 17mm under the airbox that it could come down that far to place the MAF in it's correct position. All comments / suggestions most welcome. Thanks.

[Shoppinit]

That’s weird. Most people (including Audi techs) trip up inserting the back of the air box. You can get it wrong and still screw the front down so it looks ok. It’s a terrible design.

I’m struggling to see how your locating pin receptacle could be wrong, but is there a physical obstruction?

If you press the back of the air box is there any play at all?

[IchBautAuto]

That’s weird. Most people (including Audi techs) trip up inserting the back of the air box. You can get it wrong and still screw the front down so it looks ok. It’s a terrible design.

I’m struggling to see how your locating pin receptacle could be wrong, but is there a physical obstruction?

If you press the back of the air box is there any play at all?

No obstruction, the airbox snaps into place (I put a smear of rubber grease on the two locating pegs) and all the locating bolts (one each side and one in the front align and are tight.
No play in the airbox, no downward movement over the locating peg locations, the measurements are identical on each side at the MAF location and it accords with the amount of movement that I could get at the MAF using my fingers behind the airbox before I stripped it down this time.

Who in their right mind would normally install the airbox without the MAF in place??? My thoughts were that we all may have this problem and it really is just because there is no way of seeing it in any detail once installed. Without the MAF's in place, you get an unobstructed view through the airbox to the manifold and can take all the measurements accurately. Bottom line is that the MAF's are 17mm too short to both secure to the airbox as required and also fully seat in the manifold as it has been machined by AUDI.

While I'm hoping beyond hope that someone will pull an obvious solution from an oriface, all my observations on MY car indicate a design cockup. I hope not as it then means finding a proper solution. There are many that will work but I no longer have access to machining equipment so almost what ever will be a PIA but I need to fix this before replacing everything rather than accept a boge fix again.

[Human Joist]

That could most like he have gone unnoticed mate. As I doubt anyone would have checked that before. I agree with you it’s a bad design. I’ve fitted the Apikol seals on both of mine. My current one I’ve got the mafs straight in to the housing rather than bolted to the air box. As if there is a gap for air. I would rather have it before the maf than after. Maybe some sort of extension could be fashioned for the maf to air box ?

What’s the bottom of your air box like. Do you want any measurements for mafs etc to compare it to ?

[Shoppinit]

all my observations on MY car indicate a design cockup.

Ha. It wouldn't surprise me very much. And would explain why everyone has such as terrible time getting the airbox to make a proper seal. Also why, when the back of the airbox isn't down as far as it'll go then it'll leak air in.

However, if the airbox, MAFs and seals are installed correctly then it *does* make a sufficient seal, albeit with not much of a safety margin. I personally wouldn't try to redesign it.

[IchBautAuto]

That could most like he have gone unnoticed mate. As I doubt anyone would have checked that before. I agree with you it’s a bad design. I’ve fitted the Apikol seals on both of mine. My current one I’ve got the mafs straight in to the housing rather than bolted to the air box. As if there is a gap for air. I would rather have it before the maf than after. Maybe some sort of extension could be fashioned for the maf to air box ?

What’s the bottom of your air box like. Do you want any measurements for mafs etc to compare it to ?

Whatever I do it would involve the MAF's being fully seated into the manifold. I'm tossing around about a pair of inlet trumpets to smooth the intake from the airbox into the MAF's. The airbox is like new, no issues there. I have 4 MAF's and they are all identical. Some with the audi PN and some are Bosch. I'll post up whatever I end up with that I am happy enough with to put out to the community.

[IchBautAuto]

........................................
However, if the airbox, MAFs and seals are installed correctly then it *does* make a sufficient seal, albeit with not much of a safety margin. I personally wouldn't try to redesign it.

Yes, I hear you loud and clear. Been down this road on a few occasions with mixed success, so no false hopes. My inclination at the moment is to seat the MAF fully in the intake manifold, put a 17mm spacer between the air box and the MAF flange and fill the 17 mm gap inside the airbox above the MAF with something suitable., an intake horn suitably modified perhaps. I'll ruminate on it with a glass / bottle and inspiration will surely come.

[IchBautAuto]

OK, had a close look under the airbox with an borascope, both locating pegs are sitting correctly in the grommets, down as far as they will go. All three locating bolts are in place with no force required to insert. Took some more measurements, on my car the distance from the bottom of the machined recess in the manifold to the underside of the air horn in the upper part of the airbox is 126mm. Those points are where the bottom and the top of the MAF should sit to seal correctly. The individual dimensions in the airbox and the manifold match the MAF exactly. My MAF is 110 mm long. A discrepancy of 16mm, which is the approx figure I came up with yesterday by other means. That means that in my car, the MAF body is 15-16 mm short of the theoretical length.

Other than to find that others have a MAF body that is in the order of 125mm long, which wouldn't be a huge surprise, I can only conclude that either a shortcut by using the TT MAF or a huge cockup in specing the part, the MAF's are a bodge spec in a 100K car.

I have had a look at several options and my solution in the end is to make a 15mm thick sealing flange to go between the MAF and the airbox, secured to the airbox. At that distance it is just where the MAF starts to engage the fitted O Ring in the airbox so the seal would be poor if the new sealing flange didn't provide that seal. Still to decide between an O Ring set into the flange or a tight fit over the MAF body.

The MAF will be inserted fully into the manifold as designed. There will be no need to bolt the MAF itself to the airbox as there will be minimal movement (1-2 mm) with the MAF constrained by the airbox.

Either I will be unlucky and be the only one with this discrepancy or you're all welcome to the club. I can say that it's a PIA to find something like that from AUDI, totally unnecessary.

[Gregstv]

Just measured 4 MAF's. All measure 110cm total length.

[IchBautAuto]

Just measured 4 MAF's. All measure 110cm total length.

Well, I'm glad that I'm not the only one with short MAF's, but it isn't great news in general. I spent a little time to see if I could find a longer MAF body in the catalogue but other than being assaulted with part numbers, I didn't actually manage to find dimensions. I imagine that with a huge investment in time googling each part number individually I just might be able to identify a longer body but no time for that right now.

[Human Joist]

For continuity

My maf bodies are also 110

The maf end to the stop that sits in the air box is circa 45 and the corresponding Depth available in the air box is also 45

The maf end to the stop for the car are circa 25 as is the available depth. So I’m guessing they just made the centre of the maf too short to allow for movement or they just didn’t re design for the rs and poached it off another similar model

[IchBautAuto]

Thanks very much for that, confirmation that whether in UK or OZ, the same issue appears. When I was doing a search it indicated that the MAF were also fitted to a range of Audi TT models so I'm guessing that for parts commonality they just chose from the existing range. It is likely that's why they also fixed them to the airbox, which by anyones reasoning is the worst choice with no redeeming features. It is however the only way with this design to get a full seal on each end, however tenuous. I could understand 2mm tolerance for manufacturing, assembly and in use movement, but 17mm?

[Shoppinit]

Probably designed by the same guy who designed the cruise control stalk.

[IchBautAuto]

You should complain, I have the same stalk in three cars. Talk about parts bin design. Anyway, have a temp fix on the drawing board for the MAF. Just one of many options but will get me back on the road while I look at machining options for a fix that meets the standard of the car.

[Human Joist]

You should complain, I have the same stalk in three cars. Talk about parts bin design. Anyway, have a temp fix on the drawing board for the MAF. Just one of many options but will get me back on the road while I look at machining options for a fix that meets the standard of the car.

I foresee a group but for these once your done