bouncing tacho needle

[dings]

My tacho needle has started to bounce all over the place, when accelerating hard it is ok only when I take my foot off the throttle or cruise along it happens any advice would be grateful.

[The Surveyor]

Often a sign that you have a problem with either the low-tension side of the ignition, or that your coil is on it's way out. Also been reported after swapping from ordinary plug leads to the Magnacore type high performance ones. Have you changed anything recently?

First thing to check is the wiring routes from the distributer and the coil, then the coil (can you swap one over for a short while off somebody?). If it's not there, it could be the rev counter, but from what i've read, that's quite rare.

Cheers

Paul

[That Daddy]

Yes,had a 400 in the other day with 8mm magnacors with dancing tacho,but could be coil,low tension connections etc,etc, thoughcheck to make sure none of the leads have chaffed thru on the engine components,run the engine in the dark with the bonnet up you may see the leads arcing.

[V8 GRF]

It might be the 'damper spring' on the needle that's failed. Your problem sounds like mine and that's what's happened to mine.

[nawarne]

OK, bought my 450 S plate in August - had the same indications.
I've changed the coil,HT leads, dissy cap and rotor arm (all from Tim in E.G so should be good gear). Obviously, in changing the coil I made sure of the LT connections. Result - exactly the same!!.
Funnily enough when I was test driving, I drove a 500 from Fernhursts....had exactly the same issue with the tacho needle. In fact I commented to the sales guy (Nick) was it a slight clutch slip?

Bottom line - I think it must be the instrument??
Nick

[Zippee]

Mines the same as Nick above - tried everything so guess it must be the tacho itself. TBH it doesn't affect anything regarding the running of the car it just looks a bit odd till it settles down.
Going to leave mine until I get time to have it taken out and sent away for repair.

[dings]

I had new leads fitted, we tried moving the leads around to stop this but still no good, it was ok before I had the leads fitted so it must be something to do with the new ones, dont know what to try next

[blitzracing]

If the leads are low resitance type, it can cause glitches on the coil primary, that drives the tacho' (I hate the Bl**DY things- you DONT need them). Try standard carbon cored leads ( I got a set of Lucas for a landie discovery v8 for a whole £12 on fleabay- work perfectly) , or if you prefer fit resistive plugs (NGK types have an "R" added to the plug number. Last resort (and maybe cheapest), fit an inline suppressor to the King HT lead.

Mark

[blitzracing]

Another thought, try just a resistive king lead instead of an inline suppressor, it may be enough to calm things down.

[robmarrs]

dings said:

I had new leads fitted, we tried moving the leads around to stop this but still no good, it was ok before I had the leads fitted so it must be something to do with the new ones, dont know what to try next

Yep, exactly the same problem on mine, i bought a complete new ingnition system when i bought my chim as two of the extenders were broken and the leads were old and one was split, bought magnecors from ACT, and the rev counter then jumped all over the place at idle or light load. The solution was to put the old king lead back on, it is now fine. I tried to find somewhere that would sell a single king lead, halfords do but they look crap. Spoke to clever trevor he says he can get one made to look like the magnecor with hopefully enough resistance to keep the rev counter stable. will let you know when they arrive, moral of the story is probably use standard range rover leads from rimmers and the like. You can buy 4 sets for the price of 1 magnecor set.