Messing with MFA and Eco gauge

I was looking for a gear control eco relay (171 919 091c)but the nearest I could get was 171 919 091 and that didn't work at all, so I tried using a relay with 53 printed on the top and the MPG needle moved for the first time in 10 years! The needle seems to be performing perfectly, with the needle going up and down, but the orange light won't come on While I was at it I cleaned out the T piece that connects to small rubber tube, that connects to the back of the clocks. The T piece was sooted up. Now my MFA computer is reading on average 20.2 in the city and 41.3 on the motorway, that didn't happen before as it was reading 99.9! and the Eco needle at the top is moving!

I still need to get that orange light going and ALSO need to look at a way of adjusting the MPG on the MFA.

It makes me think, if a lot of the MPG readings on the MFA is down to the Eco relay?

very interesting - which relay exactly?  Got a photo by any chance//

The relay is positioned 2 to the right of the fuel pump relay or number 4 on Hairys fuse box chart. I wouldn't recommend changing the relay for number 53 as I'm just experimenting at the moment. The relay must be connected somehow to the MFA as I'm getting good readings and the Eco meter at the top is working.

The econo relay does have some electronic gubbins in it, its not just a switch relay in the traditional sense. Not sure if its connected with the MFA though?

The change up light is also connected to the circular thingly next to the dizzy with a vac pipe and electrical wires connected to it. I changed mine and the light worked for the 1st time ever about 18 months ago. Its since stopped working again but thats agood thing as the light blinking on and off anit half a PITA

sounds good my needle has never worked and no reading on the mfa mpg but the rest works as does the orange light

I tried a small clamp on the vaccum pipe in the engine bay to see if that could adjust the MPG reading, but the reading was just the same. I pulled of the pipe completely and still nothing changed the reading on the mpg MFA!? so I removed the clocks and stripped down the vaccum sender, by removing the round black plastic back, as I did so the 3 pins just fell away

I fix digital watches as a hobby and the board looks very much the same with a matrix in the middle. Its not often that the matrix fails so will investigate at a later date.

yep - they corrode

I checked the vaccum sensor and the module was completely dead. But I was lucky to find another set of clocks in the boot of another car in the scrap yard whilst looking for a VW fuel pump relay. The speedo had been removed though and the needle was missing, however I removed the needle from my old VDO speedo and fitted it to the Motormeter speedo and it fitted. I tried the Motormeter set of clocks and the MFA MPG is working perfectly and the outside temp is reading 14 !!!! I did notice that if I remove the small block of wires (vertical block) that attaches to the back of the clocks the reading was then -31, so the problem with -31 could be down to something on the back of the clocks. The only problem I have now is a small amount of LCD bleeding. I did tried to interchange the LCD from the VDO clocks but it was slightly different. I can live with a tiny bit of LCD bleeding I suppose.

I've noticed that the vaccum sensor on the Motormeter clocks are rectangular compared to the VDO clocks which are round and that the lighting is orange/yellow compared to green, the clock casing is also slightly different. I'm just wondering if the Motormeter clocks are better than the VDO as my MFA readings are now perfect!!!

Interesting - how far does this get us.  We cannot yet identify if the common MFA fault - the default reading to 99.9mpg -  is being caused by a failure in the G55 unit (the item highlighted by arrows in the diagram below) or a failure in the processor on the circuit board (item 3 in the following diagram).  I am inclined towards the latter but I really have very little idea.

Does your experience shed any light on this?

Motometer clocks were used in a lot of cabriolets and a lot of later euro market GTIs, i have them in my sportline.........you have to be carefull with them as they have a few differences and arent as robust as the VDO ones!! and apparantly they are prone to burn out the printed circuits and clock if you jump start the car as it fries them!

Michael, the back can come off the vaccum sensor, but you have to be careful that the pins don't fall away, I just touched mine and they gave way. The matrix in the middle of the sensor unit on mine was dead but I was still getting not far off the mark MPG readings. The reading was not 99.9 as you would expect, so the problem could be elsewhere. I'm going to experiment tomorrow by removing the vaccum sensor on my fully working Motormeter clocks and see if the MPG reading is 99.9

I did notice that if I removed plug 11, with all the wiring attached the outside temp would read -31, if I pluged it back in the outside temp was correct.

Topoftherange  oh no

Today I removed the vaccum sensor from the rear of the clocks and refitted the clocks, I then drove my car and noticed that the readings seemed normal. I expected to see the 99.9 on the mfa, but it was normal. I suspect the fault regarding the 99.9 must be somewhere else. I'm going to circuit test all the tracks on the blue plastic pcb, also the board on which the LCD sits on to try and locate the common fault.

outstanding!  seems you have addressed one issue - it's not the G55 unit - even though the VW service manual recommends replacing this unit in the event of an MFA fault - I'll see if I can dig this out.

M

It appears that it's not the case with my Motormeter clocks, I don't get the 99.9 issue with the vacuum sensor completely removed. I can't really say if it would be the same outcome with VDO clocks, but I suspect it would be. Perhaps someone else can have a go to see if the results are the same?

I stripped the vdo clocks completely down to board level today. I removed the LCD by removing the two screws at the back, and stripped the lcd down. I noticed that a thin sheet of green plastic is between the the lcd and the clear plastic prism. I was thinking it would be possible to change the lcd from green to any colour you want by replacing it with say red plastic? I haven't tried this so I'm only guessing that it would be possible. I know it could be possible to change the colour of the rest of the display by replacing the 12"x1 green plastic strip at the top of the clocks case. Anyway going back to the blue plastic printed circuits behind the clocks, I looked at some of the tracks with a jewels eye piece and looks it corroded in places. I have not checked it out with a multimeter as yet. The PCB on which the lcd display tracks also look in poor condition close up but have not checked the tracks yet, I'm hoping that the corrosion is causing the MFA problems, because it would be easy to solder in new wires. Interestingly I've noticed an electrical adjuster is sited near to the back of the lcd, but I don't know what it does, anyone know what it does?

Have any of you chaps got a reliable wiring diagram for the clocks ?

Including the printed circuit board ?

Cheers……….

no but I've got multiple sets of clocks if you want to strip one down

Nope.

I checked out the blue printed circuits and it checks out ok, dispite being in poor condition. So only the PCB to test (the board that the LCD sits on) It seems that the problems with the 99.9 mpg error and the outside temp error -31 must be down to a fault somewhere on this panel. You where right Michael in suggesting the fault may be on this panel.

I've just checked the PCB board on which the lcd display is mounted. I've checked all the tracks and they are ok, I've tested 9 chokes, 7 resistors, 14 capacitors, 5 transistors and they are ok. The only components that are left to test are the 4 microchips:

1. NEC D7507G518
2. NEC D7225G
3. NEC E1903K137
4. HFF  4060BPS2

If the fault is in the 2 top chips it's curtains, I've never had any success in soldering in these chips.
If the fault is in chip 3 or 4 it is easy to solder in these chips and the board is savable.

To test these chips I need an electronic service manual to know the pin outs so I can check with an oscilloscope.

The other alternative I have is to replace the two chips 3 and 4 without testing to see if the error fault is retified. I think this is the road I will go down and will try and find these components. There is no point replacing chip 1 and 2 if I can't solder the micro chip.