Hall Sender - What is it? Is this related to 99.9MPG

Anyone know what the Hall Sender does? (See illustration below) I suspect this is the input point to the MFA and could be the source of the of the default 99.9MPG reading on the MFA but I am unsure.  Anyone have any clues?

Item (19) in the diagram is a voltage regulator.  

M

Might be useful to consider this enquiry in conjunction with the thread:

http://www.vwgolfmk1.org.uk/modules.php?name=Forums&file=viewtopic&t=16480&start=0&postdays=0&postorder=asc&highlight=

I think that's the one

And it would make sense for it to be a hall sender.

Hall sender's are switches that are triggered by a magnetic field. In this case, a magnet attached to a revolving part of the speedo.

I'm almost 100% sure that this is the sender/sensor that is responsible for the 99.99 mpg figure on the MFA.

I'm going to give my dash a going over this weekend to see if I can sort it.

AliCabrio

Cool. Now we are getting somewhere.  I have my mates at VAG looking around for replacement Hall Senders and I am trying to get hold of a second hand cluster so I can dismantle it and see the construction.

I'll also try and get through to MotoMeter to see if I can get some technical help from them.

It could as simple as a loose or broken connection to the sender


M

Hmmm - not having much luck with technocal help.  Motometer was the subject of a management buy-out about 12 years ago - part of the compnay went to Iveka and part to Bosch.

I tried the technical department of Iveka.  They know the cluster and where it was developed (Lubeck)

I tried Bosch Lubeck but the oldesty dude left in the technical division dates back to the 1990's - got stonewalled

I'll try Robert Bosch in Uxbridge but I don't hold out much hope.  I have one more card to play … see how ew go.

M

OK - I've located a new hall sender and a new voltage regulator - picked 'em up today.  Tomorrow I'm scheduled to speak with an instrument builder who worked on the VW Mk1 MFA cluster when it was first developed

Inching closer.  I am trying to get hold of a cluster to see the construction before removing mine from the vehicle.  Once I have this I'll post photo's.

Still certain all the input to the MFA is electrical - no vacuum.

M

In case you've not already found this out - I took the clocks out on saturday and started to pull things apart.

The speedo (as most other analogue speedos) works by a magnetic disk, spinning within a metal cup that is attached to the speedo needle and restrained by a spring of known tension.

So - the magnetic disk is spun via the speedo cable as the wheels go round - at a speed in proportion to road speed.

• the magnetic disk pulls at the metal cup around it (the two are NOT attached - they are only linked by magnetism). This metal cup moves only as far as the spring allows it - and as it does the speedo needle moves - and so the needle moves in proportion to speed.

The hall sender slots in from the back of the cluster to lie next to the magnetic disk - and so in theory it should detect the metal disk going round - and therefore know how fast the car is going.

Locating the sensor is easy - it's screwed into the back of the speedo with two small philips headed screws and has "motometer" written on it, as well as;

674 007 1002 and 321 907 345A

Part numbers?  :wink:

Once you've extracted it, you will be able to see the magnetic metal disk (dull coloured) and metal cup (shiny silver) inside the speedo. I took mine apart further out of curiosity, but bear in mind that if something breaks you'll need a new set of clocks….

I don't have a scooby how to test the sender at the moment.

Michael - did you get a replacement from VW?

Hi Alicabrio:

Yes - picked up the voltage regulator & the hall sender from VAG:

Part nos: 171 919 803 Regulator

321 907 354b Hall Sender.

The cluster was orginally designed by VDO, built by Motometer.  The automotive division of Motometer in the UK went to Speedograph.  There is no-one at Speedograph that I can find that has any useful information on the operation of the MFA.

The speedo is calibrated to 1000 revolutions of the speedo cable = 1 kilometer - if this is helpful.

I'll let you know when I have more news.

MP

Correction:

321 907 345B

This is identical to the nos you located except for the suffix  - "A" or "B"

Yep - that's the one.

My local VW dealer doesn't hold one, but there are a couple of places further afield that do.

Not cheap though (although I suppose that's a relative thing).

I'm pondering just buying a functioning second hand dash….but then what if it doesn't work, or conks out shortly after installation?

Decisions decisions

Ali Cabrio

OK - I've ordered the part - we'll see whether it sorts out my MFA woes.

For info, apparently the following VW dealers have the part in stock;

Keith Garages, Aylesbury - 01296 317000

Piory Park Van Centre, Hull - 01482 642020

Otherwise you have to back order from VW - although it is a current part, not yet marked as obsolete.

It cost me about ?40 (inc VAT and postage), serial no;

321 907 345B

It used to be 345A, but has been superseded.

By golly we'll beat these MFAs yet!

Ali Cabrio

PS - CALLING ALL MODERATORS - I'm up for writing a "how to sort your MFA" if that would be useful - what's the protocol for submitting? Is a word document best or a posting, or just an email?

Ali,
Tell you what, there would be a load of Mk1 drivers who would be really grateful if you could fix the 99.9 MPG issue! I think a write up on this would be excellent!

I've had my car 10 years and it's the only thing that I and a host of garages (incl BRM and AMD) have given up on!

Good luck mate - gotta admire your persistance!

Cheers!

What exactly is the 99mpg issue? Do you always get the problem even if you reset the MFA/mpg figures or is it that it soon reaches 99mpg after a bit of driving about?

My '83 GTI displays some almost believable figures for a little while before it gets to 99mpg.

Cheers,

Ross

The 99.9 mpg issue is a default reading generated by the MFA. It occurs as follows: - set the MFA to zero, drive a matter of inches and check the  MPG indicator on the MFA  - it reads 99.9 mpg - and it only ever reads 99.9 mpg.

  This following "roll test" contains further detail:

Test 1: Set MFA/ MPG indicator to 0.0

Roll vehicle to 20mph with switches off

MFA/ MPG indicator remained set at 0.0. Speedo reads as normal

Test 2: Set MFA / MPG to 0.0

Roll vehicle to 20 mph with switches open but engine OFF

MFA /MPG indicator failed - rolled over to 99.9 MPG

Test 3: Set MFA /MPG to 0.0 plus disconnect MFA plug from gearbox

Roll vehicle to 20 mph with switches open but engine off

MFA /MPG indicator failed - rolled over to 99.9 MPG

Test 4: Drive vehicle normally with MFA plug disconnected at gearbox

MFA performed normally ( distance / average speed / oil temp / clock / outside temp but not MPG indicator)

Results:

1. MFA / MPG indicator is not driven by engine generated vacuum
2. All MFA input is electrical
3. MFA gearbox output is a dumb switch: does not provide input data to MFA
4. All distance / speed / MPG input data taken from speedo
5. Inputs in (4) only available when speedo has power

Yep - I confirm all of that.

The part both Michael and I have sourced (321 907 345B) is different from the version originally fitted (345A) and seems to be the reason the MFA gives up on measuring MPG. Perhaps the B version is more reliable than the A (although it may just be the result of a change in manufacturer of the electronics/slight refinement of the process).

You'd be right to question the point (sanity) of trying to fix something that's completely irrelevant to the fundamental operation of the car, but the voices made me do it, and you don't mess with the voices. :naughty:

Ali Cabrio  

Nice bit of elimination there guys. I hope you're right.

Both the later cabrios I've owned have always had working MPG readings so maybe it is a superceded part that resolves the problem.

Those voices are telling me that tonight I'm to dig out some hi res images of the back of the guages I've taken over the years to see if I can spot some part numbers! :wink:

Like I said though, The MPG on my '83 doesn't go to 99mpg straight away, it's after a couple of miles or somertimes a few more.

yea mine reads approx double the real MPG and then eventually 99.9.

I'd like a fix too

Last time I had it out the change up light had stopped working also  :cry:

Hi All,

(1) for the last post - the change up light problem will most likely be the vacuum tube that connects to the back of the air box - it has either disconnected or it has developed a leak.  I'll get a photo for you over the next few days

(2) I have spoken to a Mark 1 expert at VW (ahh!)  He confirms that the 99.9mpg problem is endemic in the Mark 1 Series 2 MFA functionality.  The problem stems from the pins that form the connection from he speedo to the the MFA.  These pins are very small and are subject to corrosion.  Corrosion is evident when the pins turn green

Perhaps Alicabrio can provide further details (perhaps EVEN a photo) as he has a dis-assembed spedo to hand.

I am assuming the pins referred to are those that connect to the Hall Sender to the MFA

M

Michael,
When you say change up light problem, you mean the light that comes on at about 2000RPM in 1st, 2nd, 3rd and 4th gear?

The problem I have is that my light stays on >2000RPM in FIFTH gear. My understanding is that this is an issue related to the switch on the gearbox i..e it is electrical?

On a side note, I recently steam cleaned the engine bay and for about 2 days the analgue MPG meter would kivk in and the light stayed off!! So this would point to electrical gremlins. (Plus my reverse lights no longer work, so I reckon that switch is well and truly knackered!)

Cheers
 

Interesting discussion, can't wait for a final solution!!!
Surely, the Hall sender must also provide the reading for the mileage covered on the MFA….mine gives a dead acuurate reading for mileage compared to the odometer, and yet I get very high mpg readings, which are clearly wrong - they don't stay at 99.9, but are always about double expected - as mentioned above. Surely there must be a link with the vacuum tube, otherwise the mfa doesn't have any information as to how briskly or gently the car is being driven - speed readings alone won't do this…
I've cut the wire to the economy light, as it came on in all gears whenever it felt like it, but then I don't have the proper mfa gearbox plug, or indeed a gearbox which would fit it, presumably due to a gearbox swap in the past…
Keep talkin, this is good stuff!