Kato RPM Guage Reads Oddly at Idle

Hi Chaps and Chapettes, just a quick one here. I've noticed recently that Katos rpm guage is reading 2,000rpm at idle even though it is actually 1,000rpm, then as I increase the idle to 1,200rpm it drops on the guage from 2,000 down to the correct 1,200rpm. After that the guage works as it should.
Any thoughts?
Cheers Bell.

 

Have you cleaned the potentiometer on the tach?

I fixed mine that way, but it was showing 1/2 the correct RPM not double, but the potentiometer is used to properly calibrate the tach at the factory so it may be a possibility.

See post #7 on in this thread: (lots of good tach info there too)
http://www.ferrarichat.com/forum/mondial/262520-88-mondial-tachometer.html
Alden

 

Hey Alden, good shout, thankyou very much, I will check it out and report back.
All the best Bell

 

I'd wager the probability is that you'll have to do something with the tach itself as Alden indicated (although your symptom seems more "noise/crosstalk"-related as you aren't having trouble all the time), but a couple of easy things to try before that are:

1. make sure the grounding at the DigiPlexes is in good shape, and

2. swap the DigiPlex connectors (only one of them creates the tach signal IIRC, and this also gives a "wipe" to all the connections).

Just a thought...

 

OK Steve, cheers I'll try that also. Raining here at the moment so I'll wait till its fine. Kato is still our favourite out of the 2 Ferraris we have. Last weekend we went on a 6 hour drive to nowhere.... You know just mooching about. He's actually a really easy car just to mooch in....just goes to show it doesn't always have to be sideways action, te he.

 

I had some ghost tach behavior myself - I ended up taking it to Palo Alto Speedometer, they fixed it for about $170.

Here are instructions for the (t) not sure if it applies to the others but I would hope they are similar

Steps to remove tachometer

1) Using a flathead screwdriver, remove black plastic panel face (snaps off)
2) There will be four screws holding the tach into the windshield, remove those. Be careful not to remove the 4 screws that connect the silver face plate holding the tach into the casing: you want to remove the 4 screws on top of the white plastic.
3) The tach will come right out after you remove the screws.
4) VERY IMPORTANT: once the tach is out label each of the wires and terminals with some colored tape or other marker. All the connections/connectors like similar so you’ll want to make sure you know how to connect back.
5) There are 5 bulbs, 3 terminals, and two clip connectors.
6) use a tiny flathead screwdriver to carefully pry the bulbs out of their sockets
7). Use a needle nose pliers to remove nuts/washer from the 3 terminals.
8) the two clip connectors come right off
9) the lighting stalk knob comes right off.

I see you can also buy some off ebay for around $100 so that might be more economical...

If nothing is wrong with the tach, they should be also able to tell you - not sure how much a diagnostic would cost -- but i would venture to say probably not too much!

Cheers
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The rev counter is in fact a frequency counter. If it shows at certain revs a double reading than the rev counter could be ok. I would suspect in the first place the signal to the rev counter is distorted for example due to a bad ground or a bad connection. In that case a single period of a block wave can trigger the input of the rev counter twice instead of once, leading to a double reading.

 

DeoxIT is your best friend when it come to cleaning the tach potentiometer....

CAIG Laboratories - Home of DeoxIT® and Hand-E-Glove®

Brock

 

Terrific info here as always Folks, I knew that I could relay on you. I'm flat out busy, not even taken any of the cars out, this weekend looks like the same. As soon as I get the chance I'll do some investigations however by then I'll probably have Kato withdraw symptoms and will just want to go out and drive him rather than fix him