MFA woes. Can they be fixed?

The MFA on my 1983 GTI tintop gives inaccurate information and I wondered if there's anything I can do about it or is it beyond repair.
The clock is accurate and the mileage trip is also accurate but that's about as far as it goes!
The outside temperature reads lower than it actually is in the warmer weather (I don't know what it does in the cold!) and it will change by several degrees in one jump and then change back again.
The oil temperature guage reads quite a bit lower than the VDO gauge I have fitted and that also changes suddenly, for example. it could be reading 102 degrees when the VDO is reading 120, then suddenly it could be reading 88 but the VDO is still reading 120! If I give the car a bit of stick the VDO might climb to say 130/140 but the MFA reading will drop!
The MPG says 99.9 on both settings, if I reset it then it soon goes back to 99.9. I can dream all I like about the cars fuel economy but it only gets mpg in the low 30's!
I'm not sure about the average speed readout, it always seems a bit low to me but I've never tried to work it out.
I have searched and read posts (including one that was several pages long) but I haven't found a solution.
Can anyone shed any light on this or point me in the right direction as to where I should start?
Cheers.
 

Not sure the VDO oil gauge is right, 120 in normal driving and 130/140 is very high, mine sits at 90 in normal driving, 100 if sat in traffic and 110 if hammering it.
I get similar readings on my Scirocco and that has a VDO gauge and no oil cooler, the Scirocco will creep up to 120/130 if driving down the motor way on a sunny day at 5,000 rpm for an hour.

I would check the condition of the wires especially at the spade connecter as they can just be hanging on by a few threads of wire.

Do you have a heavy right foot or lates of town driving to any get in the low 30 ?
I easily get 38+ mpg in my car when I commute to work and I do reach 60 mph along some of the nice country roads.

The VDO may not be right, it’s an Audi 80 gauge wired to a sensor on the oil cooler housing. Is there  any resistances that can be used as a cross reference to see what the gauge reads? As for the mpg, the econometer reads in the 40’s when I’m on the flat doing 60mph but if I work out the mpg when I fill up it’s normally around 33mpg. I don’t get on the motorway very often and I like to stretch the cars legs from time to time.
Is there a way of testing the outside temperature sensor?


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Reading my last post tapatalk doesn't send the message correctly!
So it's an Audi 80 gauge, econometer reads in the 40's when on the flat at around 60 but if I work out the mpg when I fill up it's around 33mpg. I don't get on the motorway with it very often.
On the subject of the VDO gauge, I've just had a look and I've swapped the wires around on the VDO and MFA oil temp sender (I did this a while ago as the VDO was reading very high). The original sender is white, the new one I installed for the VDO is black. Just been reading online and I'm wondering if the VDO should have a blue sender (180 degrees) which would explain the VDO gauge anomolies. Could anyone confirm this?
Going back to the main issue, is there much I can check on the MFA etc or is it old electronics gone terminally bad?

If the MFA is showing the display and cycling through the functions it's properly the sensors or wiring to the sensors that is faulty.
I'm no electrical genius like rubjonny or briano1234 so I could be wrong so hopefully they will chip in and help.

Other things to check is earth wires, have you got 2 on the rocker cover, a big thick one going to the coil bracket and a thin wire going into the loom with the dissy connection, water and oil temperature wires?
That's how it is on my 1988 cabriolet..

Thanks for the reply. I'm ok with electrics and I understand how they work but I don't know how the MFA works but I hope you're right about it being sensor/wiring faults.
I have a yellow/black wire on the rocker cover and a green black wire to the oil temp sensor for the MFA. I can't see any other wires on the rocker cover. I don't have a big wire going to the coil bracket either. I didn't check the dissy or water temp wires (I'll have a look tomorrow). Water temp gauge in dash works ok (I think).
Most of these sensors must have a resistance at given tempertures so I can test the resistance of the sensor and also give the gauge a resistance and see what it reads. I don't know how the MFA gets all of it's data to come up with MPG though, I know there is a transducer onthe speedo which mine must be getting as it knows trip miles and average speed so something else must be wrong for it to tell me I'm getting 99.9 mpg.
Does your MFA tell you you're getting 38 MPG Mark?

MFA is a little over what I get as I worked out my MPG the old fashioned way.
MFA show about 40-44 and I'm getting 38-40.
I do live in Somerset so not much town driving even on my commute to work.

Yours being a tin top uses a different system to read MPG than mine, I don't have all those vacuum hoses and the big plug on the gearbox for the shift up and 5th gear MPG I've just 2 wires for the reverse switch on my gearbox.

My MFA does have a mind of its own, 80% of time it works fine and shows MPG, average speed and miles travelled and 20% it does not show those at all!
Everything else works just fine, e.g. Time, oil temp and outside temp.
Mine might just be the connection to the instruments as I'm planning on bulking out the connection with a bit of tape to get a better connection when I need to remove the instruments again for new bulbs etc….

white is correct for the MFA oil sensor, black is not correct for any VW oil gauge its for coolant gauges (assuming oem sensors)

depending on where the vdo oil gauge came from you either need a white sensor again, or a blue one.

check tghe earth to the side of the head for the dash clocks, its a brown/white wire with ring terminal. later cars have an extra earth strp from the rear corner of the head to one of the coil mounting bolts so thats worth a try. make sure the gearbox earth is good as well

Thanks for the replies, I've replaced the oil temp sender for the VDO gauge with a blue 180 degree sender. My VDO gauges are from an Audi 80 I think and the oil temp gauge ranges from 60-170. It now seems to run at 100 degrees with normal driving (instead of 130 with the old sender).
The MFA oil temp reads around the same but suddenly it will drop by 10-20 degrees. The ambient temp reads about right (similar to my van and the wifes car) but that will also suddenly drop by 8 or more degrees and the mpg reads 99.9 al the time. I have the earth to the rocker cover (brown/white) but I will put a link from the rocker cover to the body and see what happens.

Don't discount the earth lead on your instrument cluster.  (brown wire, usually pin 2) can become iffy, and is why I suggest that you place one piece of tape on the tongue of the plastic (remove the shroud and mylar) pin side under the mylar wrap.  To tighten up the pins connectivity to the connector on the plug… I also advocate that you splice in a Frame ground about 6 inches back from the connector on the cluster so that you are getting a more direct ground to the cluster, other than the Star Ground.

also check the pins themselves, with age they can get a bit squished. if you open the flap on the rear of the clock plug you can pull all of the pins out to bend them back into shape. Do this with the ignition off, and fuse removed for the clock so there is no voltage to any of the pins

First of all, thanks for the help so far.
I've remade the earth to the rocker cover and also ran a 6.0mm earth from the rocker cover to the battery earth terminal. It has made no difference to the MFA readouts so I'll be removing the dash in the near future. With the dry weather we're have at the moment I'm still enjoying the Golf so the MFA will have to wait.
mark1gls I've just filled up and worked out the mpg and on the last tank I got 37mpg. That was a mix of enthusiastic driving and steady driving all on A roads and town driving so on the motorway at a steady pace I should get a bit more hopefully.
Updates to follow…….

Mpg sound about right.  

The mfa mpg reading is not very accurate in my experience, my first gti which was only 6 years old when I got it used to say 99mpg.

Even on the newer Golf's there are not that accurate like my Mk6 TSI for example. Mine reads about 10% to 15% on the low side per Litre but the funny thing is that the Km's left to drive before you run out seems to be very accurate. 🤔

As you've done the only way to be sure is to record the usage by filling the tank full. Driving till it hits about 1/4, fill again and do the maths.

But then I'm sure everyone knows that anyway! 😂👍🏼

Golf Cabrio said

As you've done the only way to be sure is to record the usage by filling the tank full. Driving till it hits about 1/4, fill again and do the maths.

But then I'm sure everyone knows that anyway! 😂👍🏼

There has to be an app for that…..

Briano1234 said

Golf Cabrio said

As you've done the only way to be sure is to record the usage by filling the tank full. Driving till it hits about 1/4, fill again and do the maths.

But then I'm sure everyone knows that anyway! 😂👍🏼

There has to be an app for that…..

😂

I only know of two.
The calculater on my phone or pencil and paper for us oldies. 😉

But Brian what fuel consumption do you get from your petrol Cabrio using the Imperial measurement per mile on average? 🤔 ☺️

Sent from my Smartphone 📱

Well, we don't use the Imperial Gallon measurement, we just have US Gallons.

1 Imperial gallon = 1.2 gallons US.
In the 6o's driving through Canada they had Imperial Gallons.

On my 90 Cabby with 1.8 Digifant, 5spd, I averaged 40mpg on the highway @ 70mph, running 93 octane. In town I was getting 29-35 depending on if I was running a/c and or lead footing it. Cost wise the difference in octane was about 2 mpg so was the additional 50-75 cents difference between 87 and 93 Octane worth it, well to an accountant probably not.

On my 81 Diesel Rabbit 4spd the best I got was 59mpg cruising the interstate @ 55mph over the years and a 5spd swap I sold it getting 42 mpg in town when the thing was 20 years old.

On my Current Cabbies, 92, and 93 1.8 Digifants both with TNA Automatics, I get 19-22mpg in town with the difference being with the a/c on or off.  No real difference between top up or top down.  When I cruise the interstate running 93 octane I get up to 26-28mpg on Average.

I do know that in the oldie days, my 67 MG Midget consistently got 55mpg on the interstate, and my Rover 3500S V8 running 130 Av/gas Flew Down the road, and I didn't care about the mpg then….what with gas being 25 cents/gallon…..

So when I hear my Daughter praise her Prius getting 55mpg,

I would remind her that in the old days, I was used to getting 55 MPG in my Diesel Rabbit, or MG, No Batteries needed, and nothing to distract you from the enjoyable driving that Top down whistling hair and rumble from the exhaust provided….. Who needed Cup holders or Radios and Blue-teeth was what you had when you went to the dentist to show you plaque.