Revs drop when using electrical stuff, is that normal ? ?

Post by **wasserleaker** » 17 Mar 2007, 21:03

Hi all,
Just noticed while parked up, engine ticking over, [2.1 digijet] that when i put the blower fan on ,or flash main beam etc. the revs drop about 100 rpm, and wonder if its a sign of the alternator on its way out, or is this fairly normal with electrical demands placed on it, and i just haven't noticed before!
wouldnt mind having it re-wound, re brushed etc., sometime if anywhere still does that kind o thing, as they are 100 quid exchange in J.K. Book.

Post by **andysimpson** » 17 Mar 2007, 21:37

Yes its normal the alternator is working harder so taking more power from engine.

Post by **wasserleaker** » 18 Mar 2007, 07:36

thanks for the reply, something i hadn't noticed before.

Post by **matt** » 18 Mar 2007, 08:31

wouldnt mind having it re-wound, re brushed etc., sometime if anywhere still does that kind o thing, as they are 100 quid exchange in J.K. Book.

Place on Woods Road, derby alternators, charged me £15 to rebush mine
and that included him picking up the bit from Nottingham

Post by **clartsonly** » 18 Mar 2007, 16:12

I think they are only about £5 and it take a minute or two, when my volvo 740 went caputt luckily german and swedish ordered the wrong part so simply changed the bushes out instead, also I got away with telling them I wouldn't be taking the new battery either

Post by **sixsprings** » 18 Mar 2007, 16:36

maybe your idle stabilisation unit is kaput?

it's only function is to stop what you're experiencing...and all works fine without it.

in my experience...when they break..the car stops and won't restart until it is removed from the ignition system, so you're lucky

Post by **mahatmacoat** » 19 Mar 2007, 14:13

Your engine revs should dip by around 100rpm when you put any heavy electrical load on it. The heaviest loads are things like main beam lights & heated rear screens (if you have one).

It's also a useful quick test to see if your alternator is working - wack as many electrical loads on & listen for the idle to drop.

Not sure about digijets, but in most modern injection vehicles the ECU adjusts the idle for this & other additional loads i.e. aircon.

For the tree hugger's/hippies/tight gits out there, make sure you minimize your electrical load & you'll increase your mpg i.e. dont drive around with your heated rear screen, headlights, mega amp on if you dont need it.

Post by **wasserleaker** » 19 Mar 2007, 20:02

Thanks for the info all,
have since developed something more to worry about!
big fat cable from battery positive to starter solenoid broke orf in north wales, about 100 miles from home, must've just been holding together by a few strands for a while, as it looks green and corroded near the break at the starter solenoid ring connector.
could have been very nasty if it had earthed to the engine or bodywork

R.A.C. man 'bodged' it as a get you home fix, but needs the proper terminal crimping/soldering on again, or a new cable making up.
there's allways summat eh? keep telling myself nothing else will need fixing eventually, but it keeps surprising me!

Post by **sixsprings** » 19 Mar 2007, 20:30

mahatmacoat wrote:Your engine revs should dip by around 100rpm when you put any heavy electrical load on it.

Not sure about digijets, but in most modern injection vehicles the ECU adjusts the idle for this

it shouldn't.....T3s have an idle stabilisation unit, doing what you say modern cars ECU does

Post by **wasserleaker** » 19 Mar 2007, 21:18

Idle stabiliser unit [ beige coloured plastic box, with 2x 3pin connectors going into it] is brand new, so hopefully this is working as it should be, and compensating for any extra loads, but revs. still drop slightly when electrical stuff is switched on. revs also vary a bit, then settle down, on full lock with the power steering, as there is a sensor on the power steering pump whitch, i think, detects load and 'tells' the E.C.U. to alter the timing or revs to compensate.

Post by **andysimpson** » 19 Mar 2007, 21:25

wasserleaker wrote:Idle stabiliser unit [ beige coloured plastic box, with 2x 3pin connectors going into it] is brand new, so hopefully this is working as it should be, and compensating for any extra loads, but revs. still drop slightly when electrical stuff is switched on. revs also vary a bit, then settle down, on full lock with the power steering, as there is a sensor on the power steering pump whitch, i think, detects load and 'tells' the E.C.U. to alter the timing or revs to compensate.

The idle valves/ecu's can be slow to rspond to some changes. Just about every car has a slight rpm drop as electrical stuff is switched on or power steering demand goes up. Give the throttle housing a good clean out, the engine is then less reliant on the idle valve.