1988 Mondial 3.2 Odometer adding miles

Hi - I just got my 1988 Mondial 3.2 Cabriolet last week and love this car!

Thread about it here: https://www.ferrarichat.com/forum/threads/1988-mondial-3-2.646762/page-2

There’s a problem however, in that the odometer and trip odometer are adding on miles whenever the key is in the on position. So it has added a few hundred miles in the last week when I have driven a fraction of that distance. I pulled the instrument fuse a few days ago and that stops it counting, but obviously isn’t ideal for driving. Yesterday I had it on a hoist and pulled the connector at the speed sensor at the transmission. It stopped the speedometer but not the odometer. Does anyone have any ideas of what to check next? My best guess now is that it’s ground related. Maybe I should pull the instruments off next to take a look behind?

 

Derek sorry to hear about your trouble - I don't have the solution but re the ground - if your clock works the ground of the unit is OK as there is only one ground feeding the clock, illumination and milage counter.
Is your car a US model? Does it have the check control panel with a service due light?

 

Thanks for the reply. Good to know it’s not the ground at least. Clock functions perfectly.

I believe it is a US model, although it is a Canadian car. Not sure about the check control panel. It has all the lights in between the speedo and tach. No lights in the centre console by the shifter.

 

Sorry, no experience with the Mondial, but looking at the Mondial wiring diagrams, the odometer and trip uses the same signal as the speedometer. Most likely there is a fault within the display. Integrated circuit problem? The only other inputs are background lighting power and instrument power. I see there is an output to a mileage sensor module for the service lights. Could this be causing interference?

I have no idea where it is located. Could it be Item 21 in the parts manual?

https://www.eurospares.co.uk/parts/ferrari/mondial-32-qv-1987/electrical-ignition/electrical-boards-39155

It appears to have some kind of switch on the front. Might this affect the incrementing of the odometer/trip or is it some kind of reset?

 

Hmmm - I also have no idea where that might be located, but perhaps it is at fault.

 

Someone else also had this problem, but nearly 10 years ago...

https://www.ferrarichat.com/forum/threads/mondial-odometer-like-a-slotmachine-crazy-problem.389586/#post-141895561

The original poster didn't say what fixed it, but a new odometer has fixed this problem in the past according to one poster.

 

Yeah, I came across that one, but indeed no resolution.

I found a blown fuse in the stereo amp today which I replaced, and was crossing my fingers would fix the odometer but alas... At least now I have working tunes.

With the key on, it sounds like there is a small motor whirring behind the odometer. It was quiet in the garage and I was able to hear it. I think next is to figure out how to take the instruments off.

 

Sorry, I edited my message after you read it. At least one poster in that message thread said that a new odometer fixed the problem.

 

Your car does not have a check control system, and therefore to my understanding of the wiring diagram no milage counter module (as it would serve no purpose since you don't have a service due light) - it would be located in the front trunk rh side near the ac dryer.

Does your car have side marker lights?

 

Understood about the check control system.

Yes, it does have the side marker lights. I replaced the rear drivers side the other day.

 

So it is a US version. If you remove your milage counter/clock unit here the wire colors/functions so you know what you are looking at:

black: permanent ground for clock and milage counter
blue red: permanent 12V (for the clock)
green white #1 : switched 12V in for the clock (shows time)
green white #2 : switched 12V out to the speed impulse sensor
red black: speed impulse sensor signal via the speedo (direct, you can disconnect the speedo and still count the miles)
yellow: lights ON 12V, input for the rheostat and dims the clock
yellow purple: dimmed output to all the instruments lights
blue: unused on your car, it triggers the service milage counter not present on your car

I would take the unit out and have a good look at it. If your speedo works the sensor and related circuit is good, you have power and ground else your clock and counters wouldn't work. My best guess is that the stepper motor gets permanent 12V instead of the trigger from the sensor.

 

The speedo and trip motor wiring are spliced together, so if the odometer is getting an erroneous 12 volts, so is the speedo.

https://www.dropbox.com/t/rqEeYRHEqB6IzEfn

Sorry for the poor quality pic.

Definitely sounds like an odometer internal fault.

It's interesting to note that the odometer appears to be supplying power to the speed sensor.

 

Yes the 12V supply to all the instruments is the same - my point is that the stepper motor shouldn't get permanent 12V but the signal from the sensor. Obviously it does get permanent 12V.

So yes, internal odo fault since his speedo works correctly = sensor works normally.

I think the sensor technically isn't getting 12V FROM the odo - it's just passing through it ;-) supplying both the stepper motor and the sensor.

 

What I'm trying to say is that the pulsed speed signal from the sensor is spliced to feed both the speedo and the odometer. How can you get an erroneous 12 volts FROM the speed sensor but not affect the speedo.

Of course all power comes from the battery/alternator. It just seems like an odd way to route power to the sensor.

 

You can't. That signal is obviously correct. That's why there must be an odometer-internal fault supplying permanent 12V, bypassing the sensor signal.

Chances that someone changed the external wiring is slim = connecting something wrongly at the plug?

The only part I would check in this regard would be the rheostat - if somebody had bypassed that somehow to get better instrument lighting and by error soldered up something that supplies 12V to the odo?

 

Thanks for the comments - I was able to get the tach trim ring off yesterday without much trouble. When I have a chance, I will take out the instruments to have a good look behind the scenes as it were. I suppose that I should be able to test the voltage through the signal wire to the odometer with key on to try to isolate the problem.

I could have sworn that resetting the trip odometer many, many times (while stopped) had slowed the counting up, like maybe it loosened up or something, but after taking it for a drive, it was clicking up at its brisk pace when stopped. My 6 mile test drive said I went 22 miles...

I emailed Palo Alto Speedometer yesterday and they had a helpful reply: "I have seen this issue before. When the odometer starts counting with the key on, it tells me that a diode or transistor has failed. You will need to remove one transistor at a time, and either test or replace them."

Anyone have guidance about testing diodes and transistors? Electronics are not my strongest suit.

 

You might be lucky and find a shorted diode, but if the circuit is like the Testarossa's, you may need an expert to replace components for you:

https://www.ferrarichat.com/forum/threads/odometer-keeps-running.584869/

There are probably lots of helpful YouTube videos on how to check diodes and 3 pin transistors. Without a circuit diagram, as the man said, you will probably have to remove the components to test them. A photo of the circuit board may help us identify particular components.

 

Here a few views of a RHD odometer assembly; from the back as removed; the clock is removable (small screw to right) from this unit separately - the brown 4 pin connector links it to the pcb:

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the pcb slides out from the side:
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backside as in position - forward protruding section mid-height is the rheostat position:

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the odometer stepper motor and mechanicals are linked with 2 wires (illumination sticking straight up out of focus):
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top view of PCB, clock plug removed:
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other view:
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I have some more pictures of components if necessary.

PS the reason why I opened it up was to fix a broken LED element in the clock and my odo had a mechanical hick-up at one point - taking 100-mls number while turning the 10-mile barrel. Regreasing it all solved it. Note rheostat spiral:

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Definitely one for the experts unless there are components or solder joints which are clearly faulty (blackened, leaking, cracked).

I assume that big power transistor with the giant heatsink is for driving the tumbler motors (?).
Then you have a smaller transistor.
Some chips:
ITT SAA1004N "Frequency divider"
UA55TC "timer"
ITT SAY115Y "Tachometer"
7 (?) resistors, 8 (?) diodes and whole bunch of capacitors.

 

For me its something mechanical....the 100 meter barrel is blocked to the 1 km barrel and instead of km its counting the 100 m as km.

 

I don't think so Guido, Derek said it's spinning when the ignition is on, even without moving.

 

Thanks for the pictures - very helpful to know what I’m getting into.

 

Oh and what kind of grease is advisable for presumably the plastic gears? A while I’m in there preventative approach.

 

Something which is not petroleum based.

Google, unfortunately, has a lot of contradictory information on grease:

Ref: https://bisleyinternational.com/difference-between-white-lithium-grease-silicone-grease/

Silicone lubricants seem to be good for (low load) plastic gear application.

I see WD40 offer a silicone spray, but I don't know if it's suitable for clock gears:

https://www.wd40.com/products/silicone-lubricant/

 

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