Alternative instruments and switchgear

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syncroandy
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Re: Alternative instruments and switchgear

Post by syncroandy »

I've been doing some more work on swapping in a Passat dash panel insert, and this evening was googling in search of inspiration. I came across a thread on a Polish T3 forum, and I've got to say, they really make our efforts seem a bit pathetic !

http://forum.busikt3.radom.pl/viewtopic.php?t=3153
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Re: Alternative instruments and switchgear

Post by silverbullet »

I am amazed that more vans don't get a full dash transplant, having seen that lot.
The last one says it all really. It's a metal dash, if you can weld and form, you can make it any shape you like with a bit of effort! As for the A8 and T4 dash swaps...get you tape measures out and save a nice dash from the crusher!
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Re: Alternative instruments and switchgear

Post by lloydy »

That is some serious work there! Looks good, but i dont dislike the T3 dash that much to want to rip the whole thing out. Would like a updated binnicle though, found this place that used to sell complete plug and play dash pods
http://home.arcor.de/nolan/tachokonverter/Grimm.htm" onclick="window.open(this.href);return false;
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Re: Alternative instruments and switchgear

Post by Titus A Duxass »

That's Tobias, he's working on producing more of those digital clock sets.
To me they don't look right in a T3.

I'll be fitting a Passat set as soon the weather warms up, I've got all the bits.
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Re: Alternative instruments and switchgear

Post by lloydy »

I preferred the one in the pic below the digital pod, Mk3 golf i think?
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Re: Alternative instruments and switchgear

Post by silverbullet »

Not big on the "Digifiz" look myself.

I'm with Andy on the crappy switchgear, all #clack# instead of #click# The dash pod is a cheap-ass offering (even if the tooling probably cost a fortune) It's the one thing that really dates the SA inside.

Apart from the skinny stalks, so 1970's :lol:

I ultimately intend to move the servo with a remote unit, to free up the space behind the dash. Finding one may be the hard bit, however there were a couple of British cars that had dual-circuit remote servos with discs all round...
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Re: Alternative instruments and switchgear

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The digital dash is impressive but not 'in-keeping' with the T3, I'm trying to stick to stuff that shares the same genes. Hence the T4 stalks and steering wheel , and if I could get them working nicely the 3A Passat clocks. However the 3B ones are looking more likely as they're more flexible as regards re-configuration (can be done over the wire, vs. soldering and eprom flashing on the 3A).

I finally got round to finishing off and fitting the distance sender onto the front diff yesterday (been running with a lash-up on the end of the speedo drive). This works nicely, though the odometer is still under-reading my about 10%, and I can't seem to change the distance impulse number (K-value) in the eprom without causing a checksum error, so I may have to resort to an external box to correct this.

PS. Has anyone got a table of fuel tank volume vs. resistance, preferably for a T3 Syncro ?

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Re: Alternative instruments and switchgear

Post by Aidan »

there's some figures in bentley for the fuel guage but they rely on the VW machine which obviously is calibrated

if you have a spare fuel tank you could remove the sender and measure the range, but I bet it is similar to the curve on the temp sender

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Re: Alternative instruments and switchgear

Post by syncroandy »

Got a spare sender here, thats no prob. However the shape of the tank is such that I'm pretty sure fuel volume vs sender deflection/resistance is distinctly non-linear. There's a lookup table (aka 'map') in the 3b passat cluster that I've had to tweak as the car sender resistance curve goes the other way. Right now its roughly OK, but it'd be nice to tune it to be spot on. The cluster internally actually maps ohms->litres, then litres->gauge needle position. You can get fuel litres remaining via obd. I have a tank here, if i had 80l of fuel sitting about i could pour it in and check the resistance for each 10l...
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Re: Alternative instruments and switchgear

Post by silverbullet »

I'd have said that the syncro fuel gauge is very approximate at best, about as bad as most LPG ones i.e "that must mean full" (maybe) then "there's lots/some left", then "I'm really chancing it now" :lol:

Definitely less accurate or linear than a 2wd tank by a country mile.
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Re: Alternative instruments and switchgear

Post by axeman »

this looks quite nice found on the samba

http://i43.photobucket.com/albums/e356/ ... GP4430.jpg" onclick="window.open(this.href);return false;

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Re: Alternative instruments and switchgear

Post by syncroandy »

Right, a bit of progress to report on the 3B Passat cluster, the fuel gauge is fully sorted !

Image

The problem was that the resistance characteristic of the Passat fuel sender is the opposite to that used on most earlier VW's, including the T3, T4 and Mk3 Golf.

It now is reading the correct way round, and zero with an empty tank, 1/2 with a half-full tank, and full with a full tank.

Plus, via VAGCOM/VCDS, it is actually reading the correct fuel volumes in litres, all the way from empty to full !

To get definitive T3 sender data, I spent all yesterday afternoon siphoning all the diesel out of my pickup, and then re-filling it, 2 litres at a time, all the way to 70 litres, recording the sender resistance at each point.

I made use of Excel to record the data, and to determine the best-fit curves from which I was able to derive the new values needed. Its a bit too much data to post up here, but as an example here's the Syncro vs Passat sender resistance data:

Image

It took quite a bit of time and effort to achieve this, I've been tinkering with it on and off since last year. The most time has been taken figuring out the necessary changes to the onboard microprocessor EEPROM, which it uses for various data, eg.

Fixed configuration data such as tacho and speedo scales, petrol/diesel etc.
Variable configuration data changeable via adaptations in VAGCOM, such as auto/manual trans, fitted options, service interval reminder and so on.
Security data such as immobilizer codes and keys
Odometer data, eg. total and trip mileage

Aftermarket software is available, which using a generic ODB cable can read and write the EPROM, and modify the behaviour of the cluster. Some of the configuration data is well understood, and standardised across many versions of cluster. The software can make 'automatic' changes to this data, however most of the data is not so well understood and any changes must be made by manually using a HEX editor, on a saved dump of the EPROM, based on guesswork, experience, and trial-and-error.

After some time spent on various internet forums, I was able to establish that the data controlling the fuel gauge is held in three main tables, plus a few other bits I didn't have to be concerned with. Each table contains 8 data points, corresponding to 8 gauge needle positions, and the microprocessor controlling the stepper motors interpolates between these resulting in continuous smooth needle movement. The 8 positions are Empty, Reserve, 1/4 Full, 1/2 Full, 3/4 Full, 'Nearly Full', Full, Full (yes, twice).

The first table contains values representing the resistance read from the sender by the gauges A/D converter. I think its purpose may be to cope with the non-linearity of tank/sender. I had to modify this to accommodate the lower resistance of the T3 sender, and its different characteristic curve.

The second table contains values which map the actual fuel volume to the resistance of the sender. I had to modify this table, (a) to reverse the mapping fuel volume-> resistance, (b) modify total volume 60-70l to cope with the T3's larger tank.

The third table I didn't have to change, this determines the physical stepper motor position for each of the eight needle positions.

For testing the EPROM changes I used a spare Syncro tank sender rigged up to a cluster on the bench.

Image

One problem I had was that at absolute 'Full' reading (minimum sender resistance), the Passat gauge would suddenly drop to zero ! After some research I established this was because the cluster has a predetermined minimum feasible sender resistance, below which it assumes a sender fault and logs a fault. I simply worked around this by adding a 10 ohm resistor in series, and adjusting the A/D converter table slightly.

This may all seem completely OTT, but I feel it was worth it, as I am completely committed to using a more modern instrument cluster, and it has to be 100% functional are else it would be just annoying. Having accurate fuel data is if course important when trying to reliably establish engine fuel consumption. Finally I have the satisfaction of having the most accurate Syncro fuel gauge its possible to have !
Last edited by syncroandy on 31 Mar 2013, 18:09, edited 1 time in total.
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Re: Alternative instruments and switchgear

Post by lloydy »

Good work Andy, you must be well happy :ok
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Re: Alternative instruments and switchgear

Post by Fin »

Looks amazing, wish I could upgrade my dash - Love to plumb in something more modern and lighter
I'd love an audi TT set up
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Re: Alternative instruments and switchgear

Post by ewenmaclean »

Amazing Stuff as always Andy - really impressive you had the skills and perseverance to figure out the right values. I'm looking forward to seeing what else you'll figure out - flux capacitor?

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