2 replies to this topic

[Mothy]

1992 998 with a random bouncing tach needle.  When bounces (example cruising 3000 rpm will see bounce to 5500 and back) engine runs but loss power for 1-2 seconds.  Doesn't happen 1st 5-10 min drive and can occur as low as 1500 rpm.  One step at a time I have replaced coil, cap, rotor, plugs. Now onto points then capacitor .  Have checked plug leads visually.  Voltage regulator? Anyone been down this road?!

[Spider]

It can be from a wide variety of causes, some being (and that you've already covered);-

 

     Points

     Condensor

     Coil

     The Tacho itself

     HT Circuit tracking somewhere

     Alternator (and usually from it being on the way out)

     Bad Earth

     Something that makes electrical 'noise' - while not exactly helpful this is to cover odd ball things

                like a 'clicking' relay or something that can induce 'noise' in to  the electrical system.

 

Of these (and its not a complete list), the Points, Condensor, Coil and Tacho would top the list

[Cooperman]

Try taking the tacho out of the circuit. It will run with the tacho wiring disconnected then you can see whether it still has a random loss of power. if it does, then go into the basic ignition system and check the things which Chris suggests. If it runs OK with the tacho out of the circuit, then it will probably be a tacho fault so fit a new one. 

I usually change the standard tacho for a new Smiths tacho when doing a restoration on a 3-dial dash Mk.3 onwards car as the standard Rover tacho is not very good.

Anyone remember the early tachos which were fitted in line in the basic low-tension switch to coil cable. Tacho failure used to cause the engine to stop and we used to fit a by-pass wire with a switch in case the old type tacho failed on a journey. The latest pulse-counting tachos don't have this problem and are unlikely to cause misfires.