Bouncing tachomter needle and erratic fuel gauge

Good afternoon everyone,

I hope this message finds y'all well. I am writing to seek your advice regarding the bouncing tachometer and somewhat erratic fuel gauge in my 1991 Mondial T Coupe.

I am just getting to know my car as I just recently acquired it and immediately sent it for a full service upon its arrival. A full engine out service was performed. After taking delivery I drove the car home for about 1.5 hours, and out to dinner near my home the following evening. The next morning the car started but died in traffic.

Upon further investigation by the shop, a short near the battery cutoff by the right headlight was discovered. They also cleaned other chassis grounds. Other work was also done to cure a related engine cutting out/surging condition.

The car now runs beautifully but the tachometer does not mark correctly. It sometimes is marking anywhere from 2 to 4k rpm at idle. It does seem to mark correctly once the car is underway and at a steady cruise, otherwise it is all over the dial. On a recent trip I had a slight scare in traffic as I had started out about an hour before with a 1/2 tank of fuel, but looked at the fuel gauge and it was marking almost empty.

I immediately began to look for the nearest exit, and kept looking at the gauge, and suddenly it was marking slightly less than 1/2 again.

Previous to the electrical work the car was experiencing some surging and a cut out condition but the gauges were functioning normally.

I have been driving the car almost daily to see if it might clear up on its own. The biggest problem with the car is that it has not been driven. It's a 1991 and only had 12k or so kilometers when I bought it a few months ago.

Any thoughts or help would be greatly appreciated.

 

From one Ken to another Ken, these issues are simply one of the joys of Mondial (and other era FCars) ownership

(the tach and gas tank readings, not the vehicle dying)

You're doing it the right way though, these cars NEED to be driven. Italian tune ups daily will help.

 

Thanks Ken, I will continue to drive it and see if it improves. If not I will get the shop to do more investigation later. I just wanted to finally be able to drive it as the weather has been great in Texas.

 

Have a look at the Fusebox itself. Check the contacts and relays. Might be some corrosion in there, especially if it's the original board. My 87 coupe's tach did something similar but cleared up after the fusebox contacts were cleaned up.
Regarding the fuel gauge, mine is stable while idle but easily starts moving around once I'm underway. It always returns back to the right place when the car is either idle or cruising at speed (straight line). I was advised that they all do that, but if yours is not returning consistently back to where it should be, then it could be the float sensor in the tank needs to be checked out.

 

Tach will freeze when not driven the car. Turning point has some oil that gets hard....open your tach and put a very little drop of fine oil.

 

Thanks, I'll check this out.

 

Hi Ken, two possible culprits in my opinion. 1) bad tach - solution is send to Palo Alto Speedometer for repair about $200. 2) bad sender unit, replace with KIA sender unit $25 ( search site for exact part #)

as for fuel gauge, use tripometer as a rule (I do it even though mine works) just in case it failed and I don’t know. Again could be the meter or float in tank.

 

Best thing to do for a Ferrari is drive it, and often. Agreed with you 100%

 

Have u fitted a towbar yet for the removal van ?

 

I had a 1982 Mondial 8 I just sold last month - it had the erratic tach. Mine.... Start the car, the tach stays on 0, I had to lightly tap the dash top above it EACH time I'd start it. I had no problem with it, as it was consistent and I found that a bit charming. But the car after a while out at a steady cruise would go all over the tach giving miss readings from 0 - 6,000rpm's. Never found the issue. After my major it went away for well over a month, then came back. I can't help you, other than to give you that little bit of being in the same boat so to speak. They need a weekly drive of at least 25 miles. I did that and other then it's quirks it's always had, it never developed any real problems at all. I stored mine each winter for almost 6 months, but other than that, 1-2x per week 25-30miles out in the country a bit.