MFA / 99.9mpg / Bad news and potentially some good news....

For all those with a default MPG reading on their MFA's - here is the latest update:
 First the bad news:

Part number  part number 191 907 346 A  as featured in the drawing below is no longer available - rendered obsolete in July 2006:



and despite best efforts part number 191 907 346 H which is available and featured in the photo below cannot be adapted to accommodate the fittings for 191 907 346 A



Now the POTENTIAL good bnews:

Today I spent a little time with a chap who makes aviation instruments for the military.  I left him with two instrument clusters and two 191 907 346 A units.  He is going to investigate why these units are failing and research the potential of rebuilding failed units and returning these as fully working. He is open to the suggestion of remanufacturing a batch run of new circuit boards if their is sufficient demand.

Now I need a moderator.  (Ross?)  My question is this- would it be possible to run a poll on here to see what the potential demand may be for rebuilt G55 (191 907 346 A) units might be - if it is only 1/2 dozen I won't push it - if its 20+ we might have a runner.  I have no monetary interest in this - purely as a service to others

MP

There you go! Poll added

Shame you didn't manage to adapt it. Was there any way in which you could temporarily hang it all together without making it all permanent? Like by connecting the terminals together with some wires and allowing the unit to hang about at the back of the instrument cluster (or taping it on somewhere!) while you tested it to see if replacing this unit will actually solve the problem?

What sort of costs might be involved do you think?
If I knew it would definately solve the problem then I'd be willing to pay more for a circuit board. I wouldn't want to pay more than say ?5 each to get a batch knocked together just to see if it would work. We're not 100% its this thats faulty are we?

Thanks for all your efforts :y: , hopefully we'll get to the bottom of it soon

I'd be interested, depending on cost.

No clue on costs but will revert as soon as i have a benchmark.

MP

In response to Ross's questions:

1. Many thanks for posting the poll - great help and super-quick response

2. I managed to get the 191 907 346 H unit to plug into the the 191 907 346 A circuit board but in so doing I would solve one problem (the MFA MPG readout) to create another - loss of the needle on the econo-gauge.

3. Yes -  100% certain that the failing G55 - 191 907 346 A unit is the source of the problem.

The idea is this - send in your defective G55 unit and receive a refurbished G55 unit in exchange - this way we won't run out of housings -

Dependent on costs I'll probably finance the initial batch of (lets say) x10 units so there is a stock of working spares - we'll see.

With regard to cost , the 191 907 346 H unit I purchased from VAG was ?55 so I guess we've got a bid / offer :  ?5 / ?55 - how are you left…

MP

i voted yes. But this would be dependent on price (other things on the car to do :wink:  )

Good work by the way michael.

I would dearly love to sort my mpg reading…but can't really spare the time/expense at the mo - especially having just spent eight hours in the cold trying to replace a leaking brake pipe, only to finally snap the nipple off (ouch!) the wheel cylinder when it came to bleeding…..grrrr!
Have to get my priorities right…for once!

well good luck with the brakes - I'll focus on the the defective MFA  … isn't that the topic in this post ??? think so …

Yes, sorry for going off topic with my sob story -now sorted
Have swapped my clocks recently with a set from a scrap GTI which were motometer (mine were vdo) and exactly the same problem arose - high mpg reaching 99.9 if allowed. Makes me wonder again if the problem is more likely to be related to the vacuum part of the system? I've checked for leaks, of course, but wonder if blockage or similar in some part of the piping might be responsible….The mfa mileage is dead accurate comared with the odometer, only the mpg readout being faulty.

yep - it's a real puzzle but I've got the best people around working on this.  They'll crack it.  Should have some more info next week.

Not getting much response on the polling …. perhaps either (a) the problem is not that widespread or (b) nobody cares that much.

If it's only a handful of Mark 1 drivers intereted in a solution I'll just fix mine or perhaps generate a fix for 1/2 doz or so and leave it at that

MP

Hiya Michael

Sorry for the long silence on the MFA - migth be able to try something out this weekend.

You said you managed to;

"get the 191 907 346 H unit to plug into the the 191 907 346 A circuit board but in so doing I would solve one problem (the MFA MPG readout) to create another - loss of the needle on the econo-gauge."

Did you try putting a t-junction in the vacuum pipe to run both off the same vacuum, or was the problem electrical?

I'm hoping to try to sort my MFA out sometime over the weekend.

Fun and games


Ali Cabrio

no I haven't tied the T fitting I see the solution you are suggesting.  Fitting the "H" coded part can sort-of be done but its untidy and I'm not entirly sure of the end result - I'm looking for an original spec solution by getting the "A" series G55 units working

The fall back plan is to try and adapt the "H" series part - but as I say it will be messy - certainly far from optimal if it works at all.  I doubt it will.

Travelling next wek so I'll look at this again as we move towards Easter

MP

not much interest eh…… I'll press on for the select few.

MP

Any news on this one?

Just spent the last couple of hours mucking around with my clock set, i used to have the needle working which stopped working about 4 weeks ago! But the mpg has never worked since i got the car!

Just opened up the part you have been investigating, and found the following things.

1. all three long pins were broken at their solder points.
2. and in the middle of the small circuit board there is a small round black item with four legs, two of the legs had come un-soldered also.

At this point i thought waheey sorted, soldered them all back together and continuity checked it and guess what, still doesnt work.

Strange thing is that the mpg seems slightly better but still way off

I dont know if any of this helps at all, but thought it was worth mentioning, defo be up for a fix on this one.

There is some progress - I think it will be possible to repair the motometer G55 units on an exchange unit basis - no idea as to price yet.

I have just acquired as set of VDO clocks - the G55 unit is if a completely different design -  made of cast aluminium and apperas to be of much better quality.

I'll try and carve out a little band width next week to look at this with the instrument engineers.  These guys work for the military and seem to be busier than normal - said something about Af-gan-a-rack or something - f'ed if I know: maybe its code - anyway I'll bug 'em next week.  Solving this MPG problem has to be more important than anything the fly-boys might be doing

Catchya

Sounds like your getting somewhere, the clocks i mentioned in my last post must have been the VDO type, as the unit on the back of them is cast alluminium,
I am now getting a max of around 60MPG on the clocks and it will not go up to 99?????????? after the re-soldering

Still have no needle or light on my once working mpg gauge????

you're deffy vaccuum to the MGP gauge  - check this out:



If this is not the problem, try discon the vac tube at the inlet manifold and sucking on - see if you have vac,

MP

This is the set up i have, is this correct? none of my manuals (Haynes or others) go into any depth on the matter

Yep - looks pretty right.  The round unit near the distributor with the green wire coming away from it is a switch.  This links into the circuit coming away from the switch on the top of the gearbox that lets the electrics know you are either (a) in reverse - reversing lights or (b) you are in 5th - econo-meter needle activates or © none of the above.

Does the needle appear in 5th?

If no lights (gear change indicator) and no econo-meter needle then my best guess is - you will have a vacuum leak somewhere.  Try checking the vacuum lines themselves - sometimes they rest against hot fittings and melt through -  so although they look OK upon close inspection they prove to be defective.

To test vacuum to the MFA just pull the vacuum line away from the inlet manifod and suck on it - you'll soon know if its leaking - much easier than taking the dash out (again!)

MP

Interesting development..which may be of no value whatsoever!!!
I've disconnected the vacuum feed to my mfa, after accidentally snapping the connection at the black/white valve in front of the plenum, above the cam cover while doing another job. I sealed up the hole to the broken valve to prevent loss of vacuum to servo.
Strange thing is, the mfa reading still reads very high, and still varies roughly according to how the car is being driven…ie even higher readings when driving gently, lower readings (down to 52mpg…ha ha!) when driving more briskly. This is happening with no vacuum feed to the mfa….

…spooky!