Fulvia Oil Pressure Sender - which one

[Huib]

Right, Dani

These devices are virtually indestructible. It is just that the contacts inside go bad.

Put it upside down in a vice and use a chisel to lift the edge of the can.
Lift the can from the bottom of the sender. Just pull it off. There are no wire connections inside.

I have a simple test set up. The sender is connected to the engine through an extension piece. I use such an extension piece from a dismantled engine. A air hose is connected to the extension piece and a black wire.
Put the extension piece in a vice.
Connect the air hose to a pressure regulator with manometer.
Connect the black wire to a multimeter. Select resistance measurement (Ohms)
Screw the sender (without cap) in the extension piece.
Connect a red wire with a crocodile clip to the contact on top of the variable wire wound resistor.
Connect the other end of the red wire to the multimeter.
Vary the air pressure between 0 and 6 bar. . Resistance should be appr. 0 at 6 bar and 300 Ohm at 0 bar. In between it is proportional. E.g. 150 ohms at 3 bar.
Note that it is not a scientific instrument. If it is less than 20 Ohms at 6 bar, it is ok. If it is between 270 and 330 Ohms at 0 bar, it is ok. Don't waste time nor risk breaking any parts by trying to get it more accurate.

Check the resistance over the full range. If there is a bad contact at one of the ends or somewhere in the middle (meter jumps to a high value), clean the thing with whatever means you have. I use an ultrasonic cleaner nowadays. Avoid bending any of the parts.

Look into the can. There is a brass contact that presses against the contact on top of the variable resistance. Clean it and bend it a little to have better pressure between the contacts when assembled.

Put the can onto the sender. There is only one position possible. You can't go wrong.

Put the sender plus can upside down in a socket such that the edge of the can sits on the edge of the socket.
Put a smaller socket over the M10 thread.
Put it under a press. Apply a little pressure just to keep the parts together.
Hammer the edge of the can around the bottom.

Test again with same test set up. I have another red wire with a contact to slide onto the contact on the can.

Note there is a fibre or rubber ring between the bottom of the sender and the can. Don't loose it. Put it into the can first and than the sender into the can.

Many senders where replaced by 8 bar senders over the years. Just last month I had a customer with a complaint about low oil pressure. The cause was an 8 bar sender put in by one of the previous owners. When I replaced it with a 6 bar sender, the indication of oil pressure was ok.

A bit more technical:
The resistance of the sender is inversely proportional to the pressure.
6 bar sender -> 0 Ohm at 6 bar and 300 Ohms at 0 bar
8 bar sender -> 0 Ohm at 8 bar and 300 Ohms at 0 bar
The difference is in the stiffness of the membrane in the bottom of the sender.

The 8 bar sender is thus 225 Ohms at 6 bar. The simple assumption is that therefore the gauge on the dashboard should indicate 3/4 of full scale at 6 bar when using an 8 bar sender. However the assumption is not correct because of the lay out of the coils in the gauge. The combination of gauge and sender is highly non linear.

[Daniele Lancia Beta]

Thank you very much Huib.
I've connected my sender to a ohmmeter and I put blast air inside; at 6 bar circa, resistance is about at 0 ohm; the intermediate values seems to be right.

But something is wrong with my sender, because in the range of 2 - 4 bar, the gauge in the dashboard, seems to be a little crazy.
Even withe the engine at idle, the gauge goes up and down.
The faston connector on the sender is new.

To test the dash gauge, I used a variable resistor, between 200 and 0 ohm, and the gauge is perfectly firmly
To test the engine, I used a mechanical pressuregauge to the engine, and seems to be ok

Today, I bought a 82205408 8 bar sender to keep as a reserve; When will I receive, I will mount so I can work on my old Veglia 6 bar, following your directions.
Thank you again Huib,
I'll let you know! (tu)