1992 Ferrari Speedometer Sensor Problem

I'm pretty sure I've got a problem with my speedometer sensor, because when I measure the resistance between the two leads from the sensor with an ohm meter, I get between 2.4 and 3.7 on the 200 milliamp scale. I've talked to Ricambi about pulling a new one off the shelf and putting an ohm meter across it, but they can't, or won't do it. I have no problem buying the part if I need it, but at $277.99, I would like to know thats it and I'm not just changing parts out. Ricambi did say they sell alot of them to replace the original ones. If anyone can help me with the spec's, I would appreciate it. Thank you.

 

What's the part number? I have a brand new one (and a working used one) for my 328 here. Think the part number I have is 116987

 

This may be just semantic ...

You measure resistance on the Ohm scale, not miliamp scale. If you were looking for resistance of the sensor, and you used the miliamp scale, then your reading is meaningless.

 

I checked mine and it is 3.6 ohms.

 

When the impulse generator starts to fail, it usually causes an intermittent failure (sometimes the speedo works; other times it doesn't!)

If this is the case I'd say it's definitely the pick-up.

$277 sounds excessive. The last 1 I bought was a 100 and some dollars; shop around.

 

You cannot just measure the resistance of the speedometer sending unit. It is not just a winding wrapped around a coil. It has a printed circuit board inside with an integrated circuit and other components. The only way to test it is to replace it with a known good unit.

Brian B.
Patrick Ottis Co.

 

If it only seems to happen when you go over a bump, it could be a bad connection at the harnesss coupling. I'm not familiar with the Mondial T, but on the 348 this coupling is near the top of the left rear shock tower, in the engine compartment, and it joins the main wiring harness to drivetrain harness, and includes the wires for the speedometer, oil pressure and water temperature gauges and warning lights, and a couple of others. I believe there are seven or eight wires in it. If the connector is loose or damaged (wouldn't be the first one) then it may be losing continuity when you hit bumps. Worth a look. It's supposed to twist together firmly. By any chance have you noticed the oil or water gauges acting up at the same time as the speedo?

Of course a failure of the sensor isn't uncommon.

Good luck!