Dodgy electrics ?

rashmore · Unread post by **rashmore** » 07 Dec 2004, 16:32

Have noticed occasionally that when after having started car, set off up the road with blowers on, the speed of the fan(s) will suddenly increase from one constant speed to slightly higher.
This effect has been observed with the lights. They will be at a reasonable brightness, then suddenly increase and remain slightly brighter.
typically happens within a few minutes within journey / engine starting.
I also noticed last night that when press horn, the lights dip in brightness for the duration of air horns parping.
Is this alternator related - has been squeaking down there for a bit but figured was the tensioner ? or simply a dodgy connection somewhere
TIA

bxbodger · Unread post by **bxbodger** » 07 Dec 2004, 17:19

The first thing you need to do is make sure the battery terminals are clean and tight, and the alternator drive belt is o.k., then check if its charging properly- if you have a multimeter put it across the battery terminals with the motor running: you should be getting 14 to 14.5 volts, increasing slightly with revs. Anything much less points to a fault somewhere in the charging system.
If all this checks out o.k. then you may be in need of a new battery if its unable to keep up with the load now winters here.

Kowalski · Unread post by **Kowalski** » 07 Dec 2004, 17:53

It could just be down to a dirty contact somewhere in your electrical system, a fuse or an earth.
If your battery is going flat, I would diagnose a problem with the battery or alternator but if it starts Ok and the battery doesn't go flat, its most probably a wiring fault.

rashmore · Unread post by **rashmore** » 07 Dec 2004, 18:14

Cheers.
Starts ok - bit lumpy ocasionally. Battery is heavy duty and about 2 yrs old (5 yr guarantee)
Will check out charging and then belt. Need to check here as been squeaking but put down to tensioner. Might be time for new belt - remove and see if squeak stops then at least know from there. then a case of checking circuits i guess

np · Unread post by np » 07 Dec 2004, 23:29

Sound normal to me.Mine does the same,mostly on colder mornings.Start it fine,drive off,about 1/2 miles later lights go brighter,heater goes faster(if set on max).Diesels take a lot of power from the battery on start up.I once had a brand new Rover 200 TD,that was the same on cold/dark winter mornings.
Still be worth doing the checks anyway.

derekjl57 · Unread post by **derekjl57** » 08 Dec 2004, 01:20

Diesels take a lot of power out of the battery when starting, and it all needs to be put back by the alternator once the engine is running. So, my guess is that the slower fans is due to the battery sucking as much power out of the alternator as it can to re-charge, once it gets closer to the normal voltage, the charge current drops off dramatically (I know this from watching the ammeter on my series 1 Landie after dumping the dynamo for an ammeter!) and there is more current available for the fans, so they speed up to the normal speed.

However, I don't have any noticable effect on my 1.9TD, so I surmise that there must be something different between our two cars. My guesses are:
Dodgy connections - check the engine earth strap (mine failed).
Alternator faulty - maybe one or more of the diodes has blown, not enough to stop it working completely, but just not enough to deliver the full current it would normally be capable of (this happened to my Disco, of the six diodes in the pack, two had blown open circuit, so it was only chucking out 2/3 of its rated current, it took ages to notice anything was really wrong, until winter came and the demand from the battery increased, and on short runs it didn't get fully charged. This can sometimes - but not always - be spotted by checking the voltages).
Good luck...

beezer · Unread post by **beezer** » 08 Dec 2004, 01:30

It is possible that you have a glow plug heater system that runs on after starting. This may account for the heater and lights coming on to full after half a mile. The drop in power when pressing horn does seem to confound this though....

Unread post by **Jon** » 08 Dec 2004, 02:48

I've had 3x ZX TD and they all did this.........................................................

uhn113x · Unread post by **uhn113x** » 08 Dec 2004, 13:17

I think Beezer has the right answer. AFAIK all XUD glowplug systems remain on for a couple of minutes after starting unless coolant temp is above a certain level; my ZX does just the same.

rashmore · Unread post by **rashmore** » 08 Dec 2004, 17:44

Thanks guys,
The consensus seems to be that it is 'normal' (citroen relativity

.
Will perform basic checks just to be on safe side.
Had a look at horn - i have two sets of air horns, one situated in usual position underneath so it can catch all the road crud, the other in the engine bay. Wiring for second has been spliced into that of first. Has got its own relay.
Ran out of time but will disable 2nd horn and see if that the cause of dimming lights when pressing horn ? Tho bros driveshaft replacement a little more important.....