Voltage unstable

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yourpete - 15 Dec 2006 08:25 GMT

During night driving I have noticed that the head lights vary in
brightness. They brighten up at about 2500 to 3000 revs and dim when
the revs drop. But when in say 4th or 5th gear at about 1500
revs(Diesel model) and I lift off the accrelator the lights
brightenup?. Strange. This will voltage varation only happens AFTER
the engine has warmed up. The brightness varation is also noted if you
over-ride the interior lights. My garage has replaced the control unit
but no change. Any suggestions. The battery and alternator have been
FULLY checked out and found to be OK.

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Michael Pardee - 15 Dec 2006 12:21 GMT

> During night driving I have noticed that the head lights vary in
> brightness. They brighten up at about 2500 to 3000 revs and dim when
[quoted text clipped - 5 lines]
> but no change. Any suggestions. The battery and alternator have been
> FULLY checked out and found to be OK.

It would help to know what year and model.

Mike

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yourpete - 15 Dec 2006 19:25 GMT

Accord 2.2 diesel 4 door saloon. June 2004

> "yourpete" <none@000.com> wrote in message
> news:951271_8f4af7ca4a55d1930a8829b577d7fdf6@autoboardz.com...
[quoted text clipped - 17 lines]
>
> Mike

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Stewart DIBBS - 15 Dec 2006 21:15 GMT

> During night driving I have noticed that the head lights vary in
> brightness. They brighten up at about 2500 to 3000 revs and dim when
> the revs drop.

OK, lets look at what causes a visible variation: change in voltage. Since
you say the alternator and battery have tested OK, then its likely a
mechanical rather than an electrical problem.

What causes an alternator to vary voltage? A slipping belt is the usual
reason. A bad ground is another.

> But when in say 4th or 5th gear at about 1500
> revs(Diesel model) and I lift off the accelerator the lights
> brighten up...

Have a good look at all the alternator mounting brackets. Is anything loose?
eg the main pivot bolt on to the block. Check all the engine block to
chassis ground links.

Is the crank pulley loose or is a two part balancer type? Could be the
pulley is separating and moving the belt around causing slipage or lateral
movement in the alternator.

SD

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yourpete - 16 Dec 2006 01:25 GMT

I have thought of this route BUT this problem ONLY happens after the
engine has warmed up. This leads me towards an electrical problem and
your thoughts about a poor earth will be checked. If a poor earth
should this not have shown up when the battery and alternator were
checked?
The unit that controls electrics has just been replaced with no change
to the problem

> "yourpete" <none@000.com> wrote in message
> news:951271_8f4af7ca4a55d1930a8829b577d7fdf6@autoboardz.com...
[quoted text clipped - 31 lines]
>
> SD

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GingerGSR - 16 Dec 2006 15:42 GMT

>During night driving I have noticed that the head lights vary in
>brightness. They brighten up at about 2500 to 3000 revs and dim when
[quoted text clipped - 5 lines]
>but no change. Any suggestions. The battery and alternator have been
>FULLY checked out and found to be OK.

I had this same symptom when I swapped in a JDM B18C into a USDM 96 Civic.
The problem was the fact that the USDM car had an Electical Load Detector in
the under-hood fuse box and the JDM ECU does not use one so it was confusing
the JDM ECU and it was "telling" the alternator to stop charging when I would
press on the accelerator. I remover the ELD and all is fine now. It could be
that your ELD (if you have one) is bad, or the connection to it in the under-
hood fuse box needs cleaned.

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