Faulty Tachometer

What car do you have?

 

Ray. Sounds like it's time to pull it out and send it out. Is there a local shop that repairs speedos and tachs where you are?

If not, box it up, send it here. Take a little while, but worth it.

http://www.paspeedo.com/

They are the best guys I know to repair vintage car gauges on your Dino.

Or, buy a new one, install it yourself.

Part is available from Ferrari UK.

Part selected: 20175907 (this part supersedes other parts)

Description: 246GT REV COUNTER ASSY

Unit Price: £137.40 (GBP)

 

One of my customers had the same problem in his 246 - turns out, the Dinoplex was bypassed and he was running the engine with just the points triggering the coil.
Bob Z.

 

This may not apply, but my aftermarket electric fuel pump caused the tach needle to dance from the cycling. A relay to the pump solved the problem although I'm not sure why.

Ken

 

Hi, Ken - good point about the pump. As I recall, the Dino (and 308 cars) use a vane pump powered by a small brush type motor.
Most repalcement (aftermarket) pumps are the pulsating type. It's quite possible that they generate an inductive kick that affects the tach.
Bob Z.

 

And, since we know that Ray doesn't have his Dinoplex, and is running with just the points triggering the coil......(from a previous thread/conversation), how does he go about fixing this?

 

Hi, Ray - he did not solve it - he just puts up with it.
I still service the car and I tried to rectify the problem but the tach driver is apparently incorporated in the Dinoplex. As far as I know, there is some sort of buffering device or waveform generator to send the required signal to the tachometer. My experience with the Dinoplex is minimal - If you know a talented electrical engineer, he could probably design a pulse generator curcuit to mimic that of the Dinplex.
The only other alternative is to replace the 'plex ($$$$$$$$$$$$$$)
Bob

 

I live near Palo Alto Speedo and had a nightmare of an experience. They lost parts, did not care to resolve the issues, did not even wipe the glass clean when putting the gauge back together. I amde the mistake of giving them a second chance with my vintage radio. They ooutsourced the job, took 3 months instead of 2 weeks, lost parts, and never returned the extra hardware I gave them. And my FM stops at 92.5. Back when I was monitoring the Alfa Digest daily, it was full of PA Speedo horror stories. It is entirely possible that others have had good experiences. Search the archives on a few boards (Jag, Alfa, etc.).

 

Nick at Nick's Forza (A sponsor here) sent me a pulse generator to go with my electronic ignition that he put together for me. Might want to contact him.

DM.

 

Don't know.

I also don't currently run the dinoplex but get a completely accurate tach.

So, I'm going to take a peek today at what's going on in there and I'll get back to you with pix if possible that show what is there.

I have not yet installed nick's stuff, so I do have a modified system that gives an accurate reading.

Also, you can get your dinoplex replaced with a rebuilt one from superperformance, or you can get a modern replacement from him, too.

 

I'm running a Pertronix in my Europa, but back when I had points the tach still did the dance. IIRC, the electric aftermarket pump was getting power from one side of the coil and this was affecting the tach. For whatever reason, putting a relay in the circuit isolated the pump cyling from the tach. I had someone else do it so I'm not sure what's connected to where but next time I'm under my car I'll look.

Ken

 

Ok, guys, I think I've got the info. The resistor that needs to be placed in line on the wire going from the coil to the tach is a 47k ohm resistor. Give it a try!

 

I think the FIAT Dino list discussion is still going on about the 47 khm resistor for the tach. Not everyone has gotten it to work, there must be some other difference since it did not work for some. Myself, I have a xr700 msd and my tach is working fine, I would consider something like that before I rebuilt the dinoplex (unless you plan on showing the car in the future).

 

Yes, in my experience the regular MSD 6A or 6AL (difference is "L" has the rev limiter) works great on the dinos. And my tach worked perfectly being signalled from the MSD box once I installed it (no resistor required). FWIW, the resistor worked fine for me too while signalling the tach off the coil while I decided whether to repair my dinoplex or go for MSD.

 

The msd is pretty easy to wire up. There are instructions with it. The only new wires it will need are a switched 12v and a ground: the other wires are the same ones you would have used for the dinoplex - i.e. trigger wire from the distributor, the wire out to the tach, etc.

I didn't really notice much difference in the way my car performed either way with dinoplex, off the coil, or finally with the msd. But i suspect that having the MSD is better in the long run because it won't burn the ignition points out as quickly as running off the coil (even with the ballast it probably burns them out quicker than with an msd or dinoplex) and it also gurantees a good spark at low rpms to prevent spark plugs from fouling while stuck in traffic or whatnot.

Hope that resitor works for you in the meantime Raymond!

-Rich

 

Here is a diagram of how the dinoplex is wired on a fiat dino and it shows the modification for the 47k ohm resistor so that the tach functions without the dinoplex. Of course some wiring may be different on the 206 and 246, but I figured I'd post it for you guys anyway.
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