Don't know if this is normal behaviour, but it is annoying behaviour!
At idle (car idles at the normal 900 but <1000 rpm regardless of hot or cold) the alternator doesn't pump out enough juice to keep all my electrics running at full power. ie the headlights are slightly dimmed, more annoyingly the fan blower when set to speed 3 or 4 noticeably slows down at idle. I don't know if this is normal behaviour or not. When you need full speed fan to demist the bloody thing goes slow. As I drive along everytime I change gear the fan speed drops, the lights dim slightly.
Note I do not have any mega ampage accessories running at the same time ie this happens even with the rear screen heater switched off, no radio on, my car doesn't have front fogs etc.
Car is a 93 ZX TD just wondered what other peoples ZX's are like!
Electrical Load at Idle
Moderator: RichardW
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Guru Meditation
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It sounds like the battery or alternator are on the way out. Does the red charge light come on at low revs?
Do the simple things first: check that all the battery/aternator connections are clean and tight.
If you have a voltmeter you can do a quick check by putting it across the battery terminals: there should be at least 14v at idle with no accessories on. If its much less then the alternator may be slowly dying. The battery should'nt drop below 12 volts when the motor's turned off, either.
Most decent spares shops can do a quick, free check on your battery using their tester.
Do the simple things first: check that all the battery/aternator connections are clean and tight.
If you have a voltmeter you can do a quick check by putting it across the battery terminals: there should be at least 14v at idle with no accessories on. If its much less then the alternator may be slowly dying. The battery should'nt drop below 12 volts when the motor's turned off, either.
Most decent spares shops can do a quick, free check on your battery using their tester.
Sounds like your alternator might be dying if the fan slows to the extent you describe. My ZX (1994 1.4i) seems to have plenty of power at idle, although things dim slightly. My biggest problem is the drive belt which always starts to squeal at this time of year (and the tensioner is missing!).
I've noticed the lights dim slightly at idle on some new cars as well though (a Mondeo TDCi and a Laguna), so it must be fairly normal. A cheap tester should confirm the status of your alternator.
I've noticed the lights dim slightly at idle on some new cars as well though (a Mondeo TDCi and a Laguna), so it must be fairly normal. A cheap tester should confirm the status of your alternator.
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Guru Meditation
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The charging warning light never comes on while the engine is running-only when the ignition is on but the engine is not running. I have a multi meter at home so I'll check the voltage across the battery terminals.
I had a problem with slipping drivebelt too-most annoying problem, glad I got that one sorted
I had a problem with slipping drivebelt too-most annoying problem, glad I got that one sorted
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Jon
Funny you should mention this.
I also own a 93 ZX TD, and at idle in traffic the alternator does seem to struggle a bit to keep up, especially if the heater fan is on, plus the headlights and HRW. Its done this since I've had the thing and does not worry me unduly.
I think you'll find that on the early 1.9TD ZX's (non Volcane) they were "blessed" with a 50 amp alternator, which was soon changed to a 70 or 80 amp version as fitted to the Volcane TD.
Valeo, Bosch and Hella replacements are all 70 or 80 amp for this application.
I also own a 93 ZX TD, and at idle in traffic the alternator does seem to struggle a bit to keep up, especially if the heater fan is on, plus the headlights and HRW. Its done this since I've had the thing and does not worry me unduly.
I think you'll find that on the early 1.9TD ZX's (non Volcane) they were "blessed" with a 50 amp alternator, which was soon changed to a 70 or 80 amp version as fitted to the Volcane TD.
Valeo, Bosch and Hella replacements are all 70 or 80 amp for this application.
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blueboy2001
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Hi,
Just as a quick check turn on your lights at idle and then rev your engine a little, if you see your lights brighten a little then its a good bet your alternator is working.
Another one is to turn off your engine, turn on your lights and then start your engine again. If your lights almost go out check your battery.
Just as a quick check turn on your lights at idle and then rev your engine a little, if you see your lights brighten a little then its a good bet your alternator is working.
Another one is to turn off your engine, turn on your lights and then start your engine again. If your lights almost go out check your battery.
Guru,
Although possible it is unlikely to be your alternator from your description. Modern power electronics in the alternator are pretty reliable (awaiting the barrage of abuse for that statement!).
A more likely cause is a high resistance (bad connection) between the output of the alternator and the point at which the battery/alternator feed joins with the main supply feed to the harness.
To discover the location of the fault try the following tests with your multimeter in the order listed (all of the tests carried out with the engine ticking over and the meter set to DC volts unless stated otherwise):
1) Put the black (negative)lead of your meter on the -ve battery post (important: not the terminal) and put the red (positive) lead on the +ve battery post (important: not the terminal). With the engine running at tickover the voltage should be around 14v. If 12v then go to test 2)
2)keep the black meter lead on the -ve battery post. Put the red meter lead on the +ve battery terminal( the bit of lead which joins the cable to the battery post). If it reads 14v when it only read 12v on the post then the resistance is between the battery terminal and the battery post. Remove and clean both with emery cloth and replace having smeared with a copper-slip type grease. If not go to test 3)
3)keeping the black meter lead on the -ve battey post put the red meter lead on the -ve battery terminal. If you see more than 0.2v there is a resistance between the battery terminal and the battery post. Repair as in 2) above. If not go to test 4)
4)keeping the black meter lead on the -ve battery terminal put the red meter lead on the terminal where the largest cable is joined to the back of the alternator (put it on the threaded terminal itself, not the crimp connection on the end of the cable). If the meter reads 14v, the resistance is between the alternator and the battery terminal. Trace the cable all the way from the alternator to the battery looking for bad connections. Sometimes the big cable from the alternator joins on to the big cable on the starter motor before then going to the battery. It depends on the relative location of both items. If the reading is only 12v then the problem is that the alternator is not producing. This does not mean that it is automatically U/S. If so, go to test 5)
5) keeping the black lead on the -ve battery post put the red lead on the terminal where the small cable connects on to the back of the alternator. This is the primary feed cable. It should read 0v with the ignition off and 12-14v with the ignition on depending on whether the alternator is producing or not. If the voltage is 12v or less there's a resistance in the cable providing the primary feed. I don't know the wiring for your specific model but 99% of the time it goes like this.... The cable from the +ve battery terminal/alternator main terminal makes its way to the fuse box. It goes through a fuse and then through the ignition switch. From there it passes through the charging light on the dash and finally ends up as the small wire connecting to the back of the alternator. When the engine is not running and the alternator is not producing the light on the dash sees a complete circuit from the battery through the bulb and finding its way back to the battery -ve termional through the secondary winding of the alternator. The light glows. If the alternator is working and producing voltage (bad engineering description but it conveys the point) then you end up with 12v (or 14v) either side of the charging light bulb. Because the voltage is the same either side fo the bulb it doesn't glow.
If your charging light goes out when the engine starts, the problem is not your alternator. The power from the alternator is simply not getting to the point in the system where the lights (or other components) derive their power.
Check the battery terminals, the alternator terminals and the state of the wiring in between. With any part of the cabling disconnected try setting your meter to OHMS and measuring the resitances of the cables. If in sound condition they should read the lowest reading your meter can display. In any case, anything above 0.5 ohm is a problem and should be investigated/repaired.
It is unlikely although possible for your fan belt to be slipping and not to hear it. Pushing on the belt midway between engine andalternator pulleys you should not be able to deflect the belt any more that 20mm. However, if this was the problem your charging light would be lit on the dash.
Once the engine has started the condition of the battery is immaterial in this regard. All of the power consumed by the loads in the car are provided by the alternator, not the battery. After all the alternator still has to be able recharge the battery with all those loads switched on. The alternator capacity always exceeds the consumption of all the loads. The only time when this is not true is when the car has been modified and extra lights or a massive stereo has been retrofitted.
Hope this helps. Don't hesitate to ask any other questions.
regards
noz
ps
these tests apply to any car in the world with a negative earth when looking for an alternator fault
Although possible it is unlikely to be your alternator from your description. Modern power electronics in the alternator are pretty reliable (awaiting the barrage of abuse for that statement!).
A more likely cause is a high resistance (bad connection) between the output of the alternator and the point at which the battery/alternator feed joins with the main supply feed to the harness.
To discover the location of the fault try the following tests with your multimeter in the order listed (all of the tests carried out with the engine ticking over and the meter set to DC volts unless stated otherwise):
1) Put the black (negative)lead of your meter on the -ve battery post (important: not the terminal) and put the red (positive) lead on the +ve battery post (important: not the terminal). With the engine running at tickover the voltage should be around 14v. If 12v then go to test 2)
2)keep the black meter lead on the -ve battery post. Put the red meter lead on the +ve battery terminal( the bit of lead which joins the cable to the battery post). If it reads 14v when it only read 12v on the post then the resistance is between the battery terminal and the battery post. Remove and clean both with emery cloth and replace having smeared with a copper-slip type grease. If not go to test 3)
3)keeping the black meter lead on the -ve battey post put the red meter lead on the -ve battery terminal. If you see more than 0.2v there is a resistance between the battery terminal and the battery post. Repair as in 2) above. If not go to test 4)
4)keeping the black meter lead on the -ve battery terminal put the red meter lead on the terminal where the largest cable is joined to the back of the alternator (put it on the threaded terminal itself, not the crimp connection on the end of the cable). If the meter reads 14v, the resistance is between the alternator and the battery terminal. Trace the cable all the way from the alternator to the battery looking for bad connections. Sometimes the big cable from the alternator joins on to the big cable on the starter motor before then going to the battery. It depends on the relative location of both items. If the reading is only 12v then the problem is that the alternator is not producing. This does not mean that it is automatically U/S. If so, go to test 5)
5) keeping the black lead on the -ve battery post put the red lead on the terminal where the small cable connects on to the back of the alternator. This is the primary feed cable. It should read 0v with the ignition off and 12-14v with the ignition on depending on whether the alternator is producing or not. If the voltage is 12v or less there's a resistance in the cable providing the primary feed. I don't know the wiring for your specific model but 99% of the time it goes like this.... The cable from the +ve battery terminal/alternator main terminal makes its way to the fuse box. It goes through a fuse and then through the ignition switch. From there it passes through the charging light on the dash and finally ends up as the small wire connecting to the back of the alternator. When the engine is not running and the alternator is not producing the light on the dash sees a complete circuit from the battery through the bulb and finding its way back to the battery -ve termional through the secondary winding of the alternator. The light glows. If the alternator is working and producing voltage (bad engineering description but it conveys the point) then you end up with 12v (or 14v) either side of the charging light bulb. Because the voltage is the same either side fo the bulb it doesn't glow.
If your charging light goes out when the engine starts, the problem is not your alternator. The power from the alternator is simply not getting to the point in the system where the lights (or other components) derive their power.
Check the battery terminals, the alternator terminals and the state of the wiring in between. With any part of the cabling disconnected try setting your meter to OHMS and measuring the resitances of the cables. If in sound condition they should read the lowest reading your meter can display. In any case, anything above 0.5 ohm is a problem and should be investigated/repaired.
It is unlikely although possible for your fan belt to be slipping and not to hear it. Pushing on the belt midway between engine andalternator pulleys you should not be able to deflect the belt any more that 20mm. However, if this was the problem your charging light would be lit on the dash.
Once the engine has started the condition of the battery is immaterial in this regard. All of the power consumed by the loads in the car are provided by the alternator, not the battery. After all the alternator still has to be able recharge the battery with all those loads switched on. The alternator capacity always exceeds the consumption of all the loads. The only time when this is not true is when the car has been modified and extra lights or a massive stereo has been retrofitted.
Hope this helps. Don't hesitate to ask any other questions.
regards
noz
ps
these tests apply to any car in the world with a negative earth when looking for an alternator fault