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        General >> Problems >> erratic rev counter & alternator Whine
        
(Message started by: mattir on Nov 18^th, 2007, 5:24pm)

Title: erratic rev counter & alternator Whine
Post by mattir on Nov 18^th, 2007, 5:24pm

Hi,

I've recently bought myself a 1996 24v Ultima, which on the whole is really good. It has a few niggles which I'm slowly ironing out, however I'd really appreciate anyones thoughts on the following two.

The Rev Counter does not make much sense at all. It fluctuates wildly, bounces around and does not seem to ever give a sensible reading. Has anyone else had this problem? if so does anybody know the cause? is their a possible repair? I had a chat with my local ford dealer and I now understand that the rev counter, tacho is a combined module that is quite sophisticated and does quite a few clever things. Apparenty the part is now obsolete, however if Ford still carried it, it would cost me in excess of £300.

2nd problem, the audio system (standard ford head unit with cd changer in the boot) is suffering from alternator whine. This occurs wheather you're playing a cd, a cassette, or the radio. I can't believe it is meant to be like this, given what the car would have cost new. Also, my dads 1991 granada audio is as clear as a bell so I would hope that things didn't go backward in the intervening years. If anybody has any ideas on this one I'd also appreciate it.

Thanks.

Matti :)

Title: Re: erratic rev counter & alternator Whine
Post by martin_rowe on Nov 19^th, 2007, 8:42am

check alternator output, cleck all earths / wireing condition, could be related, tacho picking up 'noise' from alternator.

Title: Re: erratic rev counter & alternator Whine
Post by jonnycab on Nov 19^th, 2007, 9:47am

[]....It's does sound as though you may have a problem with the alternator as both your problems sound alternator related.

The rev counter works off the alternator output & radio interference, as far as I know, is caused by a dodgy alternator diode :)

Title: Re: erratic rev counter & alternator Whine
Post by martin_rowe on Nov 19^th, 2007, 3:30pm

hence check alternator / wireing, best check for alternator would be with osciloscope to check wave pattern, multimetre would be ok, would have lower output, some alternator testers can show diode fault also.

Title: Re: erratic rev counter & alternator Whine
Post by mattir on Nov 21^st, 2007, 1:02pm

Hi Guys,

Thanks for all your thoughts, these are much appreciated and may well have saved me from pursuing a couple of dead ends! From what you've all said, faulty alternator diodes would make a lot of sense. In fact the bahviour is very reminiscent of that I've experenced with other Fords when jump started with flat batteries. The Tacho's on all my old Xr2's used to jump around like this until the battery got a bit of charge in it and damped everything down. I'll definately have a look and see if I can isolate this as the cause.

Thanks again.

Matt