Alternator belt tension? Fixed: new alternator

[smegballs]

So my car seems to have a systemic electrical 'pulsing' problem. Intermittent but worse with high electrical loads, ie headlights and blower on. All the lights pulse in brightness at about 1Hz and you can hear the heater fan speed vary in time with the pulsing.

With the hood open there is a audible, but not that loud, eeeee, eeee, eeee noise that is in time with the headlight pulsing. Noise does not go away with revs, but does get louder with higher electrical load.

Is this likely the belt being (just) too loose. Ie it is repeatedly losing and regaining traction (and thus alternator output) leading to the pulsing on noise and sound.

Multimeter on the battery gives 13.6V idling and up to about 14.2V with revs with the lights off and only 12.8V or so at any revs with all the lectrics turned off...

[carlosvalderr...]

If the belt was really slipping it'd be a very noticable screech. Typically coming from old Peugeot vans being caned from cold at about 6am. From the description, it sounds more like a worn bearing grumble noise?

Unless the car is quite old, early 90's or so, it's unlikely to have a manual tensioner, most are either spring loaded or powered by engine oil pressure, like a camchain tensioner. As such, there may be little you can do to affect the tension.

In reality, it sounds like your alternator is on the way out, 12.8V with no draw isn't very good. The voltage irregularity might point to the regulation circuit. As the voltage drops, the regulator should bring it back to 14V or so.

It's worth checking the AC voltage across the terminals as well as the DC. If the AC is anything more than a couple of tenths of a volt, the diodes in the rectification circuit are dying and letting the generated negative AC leak out. Some poor terminology there, but you get the idea I hope...

It might not show anything, but get the car in the dark, engine on, lights on but everything off, and shut the engine down. If the headlights become brighter, or not noticably dimmer, the alternator isn't providing enough current. This is assuming you have normal lights and not arc type HID lights.

[smegballs]

It is 95 Subaru Legacy, so yup pretty old! And does have a manual tensioner.

Well I had a play today, and am in agreement that the alternator is fucked. The fault seems to be intermittent in that it only occurs for 3 mins or so, then 3/4 mins of normal output and operation, then 3 mins of pulsing etc etc. I imagine that the time that it is working is what is keeping the car running/starting fine.

Luckily it will be a piece of piss job to swap out the alternator (it's almost as if the engineers designed this to be easy to work on, everything is in a sensible place), which I defo want to get fixed before doing any outback driving....

Playing about with the revs today, when it is in 'pulse mode' the audible whine does rise in noise and pitch when revved, so a knackered bearing does sound quite likely.

[bugeye_bob]

Where you located fella?
I have a couple of Impreza alternators but I may be able to fix yours.

https://opposedforces.com/parts/legacy/en_b11/type_7/engine_electronic/alternator/illustration_2/

[smegballs]

[carlosvalderr...]

[bugeye_bob]

[/quote]

North Stradbroke Island..... Queensland Australia

Cheers for the offer tho mate Only arrived in straya a month ago, prices on alternators aren't too bad here. About 170 bucks for 3rd party ones with 5 year warranty.[/quote]

Ah no worries, I have a mate who works for a company that reconditions alternators, and was going to send you his way, that would be a fair trek then lol

[smegballs]

Well I got a new alternator from ebay and flopped it in.

No disco-lights, steady 14V at the battery terminals with all electrical loads turned on.

Vair nice!