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High Alternator Output 9 years 7 months ago #147582

Following the cars recent emissions failure on the MOT I've changed the plugs, leads, dizzy cap and tonight got round to cleaning the idle air control valve. The car still seems to have a very mild lumpy idle, not enough to make the rev counter needle twitch but you can hear a slight inconsistency in the idle.
Out of curiosity I put my multi-meter across the battery and was surprised to see it fluctuating rapidly between 13ish to 20+ volts which I suspect is not quite right.
Is it possible that this could be causing the idle problem and maybe even contributing to the high CO emissions?

Of course it could be my multi-meter could be knackered!

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High Alternator Output 9 years 7 months ago #147584

That definitely does not seem right!
However I would be suspicious of the meter used.

Do you see your headlights flickering with the voltage changes, or does the voltage stabilize when the head lights are on? (20 volts would probably cause bulb failures, so is unlikely you actually are getting 20V)

Try and get hold of a good quality meter (preferably analogue with a needle that moves).
Failing that take it to an auto electrician to check.

Could be a failing alternator

Could it cause your problems? Who Knows...but it certainly wouldn't help!

Peter

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High Alternator Output 9 years 7 months ago #147585

Did you replace the Lambda ? this could be affecting the emissions and the idle, did you clean the IVAC too. I replaced the plugs (platinum NGK) leads with magnecor, distributor cap and Rotor arm, coil, fuel filter, air filter , Lambda and CAT and my idle is perfect steady at 800rpm (i am using super fuel BP ultimate, Shell V power or Momentum, 4500 miles on and she is still perfect. :woohoo:

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High Alternator Output 9 years 7 months ago #147591

If your alternator is pulling more power it will effect the idle/revs/power. The alternator has a diode pack and regulator inside if this is constantly switching in and out it will cause the ruff idle.

Later alternators with the extra lead to ECU cut our completely at a certain voltage (and at high revs I think)? If this is constantly switching in an out at idle it will place strain on engine and give a lumpy idle.

Most multimeters are fine for DIY use, don't buy a meter buy an alternator you can always stick it back on ebay if it doesn't solve problem. Or find some where to test it?
Like I said a couple of different alternators types so make sure you get the right one.

Let us know how you get on

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High Alternator Output 9 years 7 months ago #147594

Voltage check with Ignition off, meter set to DC leads connected across the battery, on a healthy battery 12 to 13 volts.

Start the engine and the voltage will increase, you should never see more than 14.8 volts,

If you are unsure about your voltmeter or an overvoltage from the regulator in the alternator then it's a 5 minute job for any garage.

If you go somewhere where they sell batteries the test is normally free like Halfrauds (but they will want to sell you a new battery anyway!)

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High Alternator Output 9 years 7 months ago #147632

Thanks for all of your responses.

I checked the reading on the battery in my sons clio and at rest the meter was reading around 19v so the simple conclusion is my multi-meter is the problem.

Once i get myself a new one i'll check again just in case there is an issue.

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High Alternator Output 9 years 7 months ago #147638

Thanks for updating us. :broon:
David
:shrug:

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