Tach stopped - advice needed.

[ecm911]

Just went out to start my car - been having a mild problem with cold warm up and noticed my tach did not move.

Heres what I have done.

1. checked connection at tach. - looks ok
2. Checked connections at CDI - no problems
3. Test with volt meter wires to tach - I get a read but not sure i understand it. It does vary but doesn't appear to vary with the rpms. ( used 200v av range ??)

4. also noticed tach does NOT "jump" when key first turned to on- all other gauges, except tach and speedO, do jump. No prob with speedo.


Short of replacing tach - what can I do next? Could the heat cause a problem - it sure was hot in the car - anywhere for that matter.
thanks


earl
ps - CAR RUNS FINE - NEW BATTERY AND NO APPARENT ALT PROBLEMS.

[ecm911]

ps - engine is 83 euro SC - no O2 sensor & no brain in a 78 US body.

thanks.

[Early_S_Man]

Earl,

First of all ... you need to change the meter range to 20 Volts DC. Check for +12 Volts between the Red/Black wire terminal and the negative [ground] Brown wire terminal -- on the tach when ignition switch is on.

Switch the meter range to 20 Volts AC. Check for a signal from the CDI unit between the Black/Violet 'TD' signal wire terminal and ground -- while engine is running. Make sure your clips are insulated and secure on the terminals before starting engine. If your meter has a 'Hz' position, that would also work.

[jaydubya]

Originally posted by ecm911
Could the heat cause a problem - it sure was hot in the car - anywhere for that matter.
thanks

The needle on my tach gets stuck against the plexiglass cover when the car gets hot. Grab the tach gauge on both sides and pinch it together with your fingers. If this gets the tach needle working then the plexiglass is warped and is contacting the needle when it heats up.

[ecm911]

jaydubya - thanks, but the needle moves freely in the tach.



Early_S_Man

I have 12 volts ( w/ switch on) between ground and Red/Black wires.

My meter is just a cheapy - lowest AC V setting is 200V and no HZ setting.

I think my son has one but he is away on vacation.

Anthing else I can test/try in the meantime?

Thanks Again!!

Earl

[ecm911]

Update.

Have not been able to get a better meter to check the CDI as Warren instructed.

But here is the latest. I noticed I have AC current to the battery at engine idle.

This should be - should it. Isn't this an indication of a bad alternator?

Noe 12.48 volts DC at battery at idle.

Thanks
Earl

[ecm911]

Update to update.

DC Volts at Battery with at higher rpm ( don' t know what rpm's are since my tach does not work) but i wolud guess 3500-4000.

Top reading was 13.18 volts.

Also have another question - when should the CDi whine? With engine off but ingntion on? Or both on?

thanks

earl

[MBEngineering]

HI you have the dash in bits with the speedo out also, take the speedo and wire it in to the RPM wires, that will check the car wiring is OK and you have a faulty tach to sort/replace.

regards mike

[ecm911]

Well this has got my completed confused.


After I read Mike's post - I went out to do as he suggested. The car had been seating there for a few hours - doors and engine bay open.

I started my car to listen for the CDI whine and do as Mike suggested. After here the cdi box whine ( at least I thought I did) I got back in and was just about to turn it off and the darn tach was WORKING! I swear I did not touch a thing - since the last time I was out there playing with a few hours ago!!!!! And the tach was not working then!


Obviously its not the tach, which seems to be working fine now!
Could this be the early stages of an alternator failure?
Or more likely loose connection somewhere, but where? This could be interesting to find ?


Anyway thanks to all for now!!! Any last comments would be appreciated!!!!

Earl

[Early_S_Man]

Earl,

Both the precence of AC Voltage at the battery ... and your 12.48 Volt and 13.18 Volt readings are indicative of alternator problems, and they are probably the reason for the tach malfunction in the first place!

My suggestion is to pull the fan housing and alternator, and take it to a motor/generator rebuilding shop for testing, and possible rebuild. Take your Voltage regulator with it for testing, too.

Your 980 Watt [70 Amp] Marchal/motorola alternator is the best design ever installed in a 911, so don't even consider replacing it with a later Paris-Rhone or Valeo model with integrated Voltage regulator!!!

While you have things apart ... check & clean the battery terminals for corrosion, as well as the junctions where the battery ground strap, transaxle-to-body ground strap, alternator to engine case bolt ground strap, and engine compartment electrical panel ground strap. Disassemble the battery positive connector and clean all cable connections to it, as well as the direct positive connection at the starter solenoid After wire-brushing all connections and cables, clean with vinegar, distilled water, 91% isopropyl alcohol ... then apply liberal amount of silicone grease, preferably Dow Corning 4, 111, or 112 to keep out moisture and oxygen. The 14-pin connector needs very careful cleaning with an old toothbrush rather than wire brush, as the pins and sockets are silver-plated brass -- and fragile! After cleaning the pins ... spread them slightly with a No. 11 X-acto knife blade, then apply silicone grease as on all the other connections!