[misterjagman]

Does any one know if there is a procedure to test or troubleshoot the speedometer pulse generator on an 1986 Spider. My speedometer stopped working a couple of weeks ago, I have inspected the connector on the generator, and the cable going to the transmission, I removed the Monopod and checked the connections, is there something else I can check or do?

 

[Elio Comello]

Most likely NOT the generator.
Send the monopod in to Palo Alto Spedometer to check/give estimate.
Also some good threads on "u fix", but danger you will damage.
TTFN Elio

 

[Gubi]

Well, not sure I'd say that. I've had two pulse generators go bad on me. Of course, on the S4 they live down by the exhaust downtubes so they lead a harder life.

Should be pretty easy to use a digital voltmeter to check the pulse sender. Check for voltage pulses at the sender connector speedo output wire as you spin the sender with a power drill or something (this needs to be done with the ignition on and the sender plugged in, obviously). If you have pulses then it's the monopod (assuming you've ruled out the cable drive to the sender). No pulses then it's the sender.

 

[spiderserie4]

if the speedometer does not work but the mileometer/tripmeter still does, it is more than likely the speedometer guage itself.
a few useful bits of info here that i posted on AO:
alfa spider S4 speedometer - Alfa Romeo Forum

 

[pabeaver]

You are not going to see pulses with a dvm as the damping will prevent seeing them at any rpm. You would need some sort of 'scope.

 

[Gubi]

You are not going to see pulses with a dvm as the damping will prevent seeing them at any rpm. You would need some sort of 'scope.

Well, I've done it on my Milano using an official Alfa "digital test light". It's basically an LED with a resistor in series: there's an Alfa TSB on how to make one and test the pulse generator (procedure is specific to the Milano but a pulse generator's a pulse generator).

The pulses were long enough that I suspect you'd still see fluctuation with a DVM. But if that doesn't work you could always just go the LED+resistor route...much easier than digging up a scope.

 

[Alfacliff]

If you set the dvm to AC you should see some voltage that increases with speed.