Syncro fuel sending unit checking(trying to)

[ourv12]

Hi,Ive been trying to diagnose my non functioning Syncro fuel guage. With the ignition switch on I installed a wire jumper at the sending unit end (female 2 wire plug) and that should have told the dash guage to read full correct? (assuming the guage is in good working order) But when I did that the guage still read empty. So I guess the dash guage is bad?? Is there a way to bench test the guage itself?? Is there a way to test the sending unit with a ohm meter?? Are the Syncro guages prone to go kapute since they are different than 2 wheel drive guages? Any help would be great! Thanks!

[austinado16]

The wire going to the fuel tank level sender is looking for ground, so yes, removing it from the sender and touching it to ground would "Full" the needle in the dash gauge with the ignition swith turned "on."

A couple of things:
1) The gauge is being given about 9-10v viat that 3 pronged voltage stabilizer on the back of the instrument cluster assembly. Make sure you have that voltage. The temp gauge is fed the same voltage, so generally, if the temp gauge is still working, your problem would be confined to either a bad fuel gauge, a bad wire to the sender at the tank, or a bad sender in the tank.

2) If the gauge is being powered, and grounding the sender wire doesn't "Full" the gauge, you either have a bad gauge, or a bad wire. The next test would be to use an ohm meter between the sender end of the wire, and the plug-in at the instrument cluster.......by touching the ohm meter probe to the prong on the plug-in that feeds the ground signal to the gauge. If you have continuity during this test, you know you have a good wire, and therefore a bad gauge.

3) If grounding the sender wire does "Full" the gauge, you know you have a good gauge, and therefore, either a bad sender, or the sender's not grounded to the fuel tank and the fuel tank isn't grounded to the body......so you'd focus your attention on the tank and the sender, and corrosion.

Clear as mud?
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1970 Austin America
1966 Mercedes 250SE Coupe (sunroof & 4 on the floor)
1981 Volkswagen Rabbit Diesel LX P/u
1986 Kawasaki Ninja 600R
1990 GMC 1/2ton 4x4 Suburban
1995 Audi A6 Quattro Avant

[ourv12]

absolutely!! I thought I was headed in the right direction with the jumper wire,now Im checking for good ground at the fuel tank and the ground wire from the female plug at the sender. Thanks, this forum is just great!!

[insyncro]

Chances are the connections have rusted to a point that they fail.
The sender is NLA.
Only good used ones will allow for a working gauge if yours has failed.
I have some and know others who are parting Syncros with them.
Feel free to pmail me and I will send you info.

dylan

[ourv12]

After checking everything else I found out It was my guage!! Anyway I was so far into it that I decided to try and repair the guage.I removed the cluster and unscrewed the clock to gain access to the tank guage. I removed the tank guage and drilled out the two small rivets that secure the face plate. I checked for continuity at the two studs but got nothing so I new there was a break in the small wire that wraps around the bimetal strip somewhere. I could not see any breaks so I removed the small wire from the two studs (looked like they were glued on at the factory?!?!) and soldered them on. I then checked for continuity and got a reading!!! I then used a 9 volt battery at the two studs and the guage started to move all the way up to full!! I fixed it!!!!! Now I can fill up and not have to remember to reset my tripometer every time. And saved me some money buying a used cluster.

[austinado16]

Nicely done!

Great job sticking with the diagnostics and proving both, what it was, and what it wasn't.
_________________
4 little pistons hammering themselves silly
__________________________________________
1970 Austin America
1966 Mercedes 250SE Coupe (sunroof & 4 on the floor)
1981 Volkswagen Rabbit Diesel LX P/u
1986 Kawasaki Ninja 600R
1990 GMC 1/2ton 4x4 Suburban
1995 Audi A6 Quattro Avant

[insyncro]

Nice job, for sure.
Using the tripometer really gets old after a while eh?

I will save this thread to be passed on throughout the Syncro groups.
Many will try the same.
Pictures would be great.
If you have the chance to snap some on the next Syncro specific fix, it will help many.

df

[noganav]

Just to add to this thread, since it helped me solve my issue.

You can check continuity for all the parts outside the instrument cluster with an ohmmeter between position 3 (brown wire) and position 7 (purple and black wire), and work your way back if you get infinite resistance. Testing first the wire by connecting the two leads at the fuel tank end of the sender and checking continuity across 3 and 7, and so on.

My problem was in the instrument cluster itself. You should get continuity between the 3 and 7 positions on the other end of the connector as well, if you jumper over the resistor located above the temp gauge.

You can trace the circuit around, from 7 through both gauges through that resistor and back to 3. You can easily check continuity all the way around using the posts of the gauges.

My trouble was the connection that runs directly between the posts of the temp gauge and the fuel gauge, jumpering this restored the function of my fuel gauge.

[Mickyfin]

Great thread, and some really helpful info.

My Syncro fuel gauge is lazy, so I checked, and cleaned the sender connection, but still only reads just over half a tank when full.

I'm yet to bridge the connection to see if the gauge reads full, but will do when I get Syncro back from the repair shop.

[mathieux46]

Hey Mickyfin,

Any update on your lazy syncro sender or gauge? Mine does the same, reads slightly above half when full.

the fuel gauge reads full when i ground the sender wire. The temp gauge read perfect so I probably can consider my voltage stabiliser ok.

Does the sender mounting plate needs to be grounded? I will add a jumper wire to the sender mounting plate to ground it to see if it helps.

Thanks

Mat

[16CVs]

So where is the ground wire for the fuel sender ? Bentley says it is is near the ECU . Mine did not have a Digifant ECU . Info is vague as to where ground is .
HArness plug from sender goes into harness and runs forward and backward .
MAybe some Conversion guys may know . My Temp gauge is OK so I assume it is a sender problem . I have replaced the sender , SO this is the next obvious step .
Neither of Syncros have a proper Fuel gauge .
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