Alternator at fault??

Hi all.

I hope someone,somewhere can help.

I have a fault that has just raised it's ugly head and it is as follows:
I start the car and the interior light, clock digits and rev counter all flicker in time with the engine.Same happen when the headlights are on. Does'nt show so much when the engine is revved. The alternator heat shield was loose and a bit of arching is showing on it. Has the alternator been damaged?

Very possibly.

Get a multimeter put it across the terminals at the back to see if it's charging correctly if not have it properly checked out or replace it

Charlotte

Many thanks Charlotte

put yer multi meter over the battery with the ign off ,check reading then start the engine . with ign off and a full battery you should have about 13.2 volts with engine running you need to have between 13.5 and 15 volts.. i wouldn't want to be messing around with meter leads that close to the fan belts and rotating pullies...

I have a variation on this problem, at first the battery light came on with the ignition off (and managed to discarge the batery). I also noticed with this the rev counter did not work, then when driving the rev counter started to work and the battery light then came on and gets brighter with revs. The battey is charging fine I am just left with this light on the dash. Any ideas on this? are the problems linked?

Mine is a 200TDI

it could be a short in yer alt. leading up to complete failure of said alt...of course it could be a general wiring fault behind the dash.

Sounds like a bad earth fault check the earth connections, possibly picking up earth return through other components.

if it draining the battery its unlikely just to be a bad earth..

I may be mistaken but doesn't the rev counter feed come from the alternator ? take all the connections off the back, clean them up and refit them, may cure it for you.

i think your right! you are mistaken . why would you.. no.. how could you measure engine speed at the alt?
when you turn on the ign you get batt voltage earthing through the alt which puts yer red light on when alt output is higher than batt volts the alt volts cancels out the batt volts at the red light and it goes out.
trust me my mechanics knows a bit about red lights

Fair enough, but if you disconnect one of the two smaller wires from the back of the alternator the rev counter don't work ? Its the one with the eye connector on ours not the push on spade one, I found this out when i fitted a new alternator over the Xmas break.

without a diagram i can't say what the small wire is for..at a guess i'd say its somekinda power supply for the dash.. only a guess mind!!

Bad news I'm afraid, the tacho does take its feed from the alternator, white/grey wire from terminal W on the alternator passe's thru a "phase tap resistor" than onto the tacho.

So if youve got a dodgy needle on your tacho check your alternator, I had a dodgy needle before i changed it (changed because of bearing failure not a charging prob) but it also repaired the intermittent tacho needle, that's what made me go looking for it in the 1st place, 1st drive i thought that's odd, tacho's working, all ive done is change alternator, pulled wires off it stopped, put them on it worked, learn summat every day.

well if it does it not a very reliable way of doing it, any slippage on you drive belt will cause a false reading, any wear on yer belt will cause a false reading. i think it more more likely a feed to power the thing rather than a means of measuring engine rpm. then if you have no power to it it won't work which would tie in with wot you say.
i reserve the right to be completely wrong as it may be true

Just looked up the Haynes manuel wiring diagram, this shows the Tacho being driven from the alternator as Jon says, he is correct also with the fact that it goes through a Phase tap resistor then onward via a White/Grey cable.

well i'll go to the foot of our stairs!!!!! that has to be a ford idea,, so how do they compensate for belt wear/slipage???

This won't help with the original problem but hopefully a helpful clarification on diesels and rev counters...

On TD5's and later TDi's the rev counter is driven by the ECU. On older (non ECU engines), there is a 'W' terminal on the alternator that can be used to drive a rev counter... cos diesels engines dont hav sparks to count like petrol rev counters do...

wouldn't using the crank sensor be better??

I had exactly the same problem with my old 200 tdi and it turned out to be the alternator. Changed it and hey presto problem gone!

Hope this helps

Many thanks to everyone...........I think I might have sussed it's the alternator.just got to get one now!!!