Strange happenings - don't know!

[herbie]

Hi folks,

Here's one for you. When I'm cruising along on a steady throttle say at 4,000 rpm the engine is all smmoth and lovely. Then every so often the rev counter needle will jump to, say, 5,000 rpm but the engine revs obviously don't rise.

Dodgy rev counter thought I at first. Not too bothered by it. Then gradualy, I have come to notice something. When the rev counter "jumps" the engine seems to vibrate very slightly. Not a lot but it is definately there (unless I'm going psychotic!). I have tried to analyse what may be happening but I am stumped. There is no noticeable loss of power or speed and the engine is definately not changing it's rpm (like it would if the clutch was slipping), just this funny tingle....

Any ideas?


Regards to all,
Herbie.

[Jerry]

Pull the alternator cover and make sure the bolts underneath are tight. Reports in the past about these working loose over time, leading to failure in a couple cases. Check NOW.

Rev counter (tachometer) is keyed off alternator field windings, so many problems with readings can be traced back to alternator problems.

[herbie]

Jerry,

thanks for the reply. What bolts are you on about? The three that hold the "stator" in place can be checked without pulling the cover can't they? Do you mean the rotor retaining bolt or is there another set I'm not aware of? I've never had the cover off, so I'm only going by information in the manual...

Regards,
Herbie.

[Jerry]

Sorry. I meant the 3 bolts that hold the stator in place. If you can check these bolts without removing the cover, so much the better!

My XJ uses a different alternator than the XS, so checking requires removal of the cover.

In any case, check the 3 stator bolts. If this is not the problem and the tach still jumps, you may need to go deeper into the wiring. Check and clean connectors, look for worn spots on wiring insulation. Based on past comments, the problem is between the tach and alternator.

[sixtysix]

The tach is electrically driven from the voltage regulator, so look for electrical problems not mechanical ones. Jerrys got you started in the right direction.

[herbie]

Hi Gary,

it's not really the tach that's bothering me (I know when I'm over revving - things pass by too quickly!). No, it's the strange vibes from the engine that have me concerned.

I thought it may be related to the advance/retard side of thing. You know, when the tach jumps and the tingle starts, there's too much ignition advance. Is that possible? Just a thought... I'm keeping on looking up to now.

Herbie.

[Dragonrider]

Hmmm . . . have you done your cam chain tension adjustment?

Also check electrical stuff, particularly the pick up wires and the wiring to the coils/ballast resistor. Also the connectors and wiring to your black-box.

Fuses good and in solid? If you still have the stock glass fuses, they can be loose and corroded and making bad connections. You may not have proper voltage to run everything at a certian rpm/vibration.

Just some stuff to check...