Tachometer swings on start up

1983xj6 vp when it refuses or is hard to start, the tachometer swings wildly, but when it starts first time the needle does not move. Battery is healthy and it starts when hot. Sometimes when driving the tachometer swings then settles down until change in acceleration, back off and it settles down again. I believe the instruments are electronic.
Any thoughts.

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In my experience the speedo swing is always caused by excessive voltage drop. Long cranking events, a starter motor drawing too much current, poor connections.

I begin by cleaning the battery cable ends, underbody main ground, and the two “+” junction posts on the firewall. There’s a chance that this process alone will solve the problem. In any case, it’s good to have known-clean connections and grounds.

If no joy, post back




exactly. solves so many electric gremlin stuff. AKa electricery…

My ump will not start. Ugh. Out of gass? igntion goner haywire. too hot to mess with.

later, mebbe.


Thanks Carl and others,I know the battery terminals are clean so I’ll check firewall and starter terminals and let you know.

I had that too, bounce when starting. It went away but I can’t remember why, and has not caused damage. It can only be low voltage or an ignition problem (possibly caused by low voltage?).

My '87 Xj6 needle has bounced when starting since 1999 and I just learned to live with it

Deep thoughts, Testie - the taco is operated by the ignition module/coil connections - and your stating difficulties may have some bearing…?

The tacho will initially jump up some 200 - 500 rpms during acceleration due to converter slip - but should of course be steady with steady speed and rpms. The tacho is tied to ignition - a sign of ignition failure is that the tacho drops to ‘0’ while the engine is still turning. An ign amp fault may cause tacho anomalies as well as noticeable misfiring…so…?

I suggest you sort out the cold starting issues - a more tangible problem; the tacho problem is not really a vital problem even if it is something to be sorted…

xj6 85 Sov Europe (UK/NZ)

Thanks Frank, I think I have a spare ignition module, but with only one arm I’ll have to wait for help. I’ll post when I find out further.

It’s uncertain what caused the tacho’s behavior, testie - but the cold start difficulties has usually detectable causes…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

To me, te tach needle suld incicste RPM during the crank. If it does not, the engne as no spark and will not start.

woe is me. My lump failed to start. No tach movement. Failed ignition. fix can be simple or very involved.


Hi speedy cables would re condition that gauge for you…

Also look at the GM module….

It’s called AB14 ….

Make sure it’s a good quality part for the replacement…… in the GM module…. I use only myself… Pertronix D2000 Flame-Thrower HEI GM 4 Pin Module