How to test a Coil Pack? - Alfa Romeo Forum
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Old 30-11-09
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How to test a Coil Pack?

Quick question I hope.

I want to test the resistance over the coil packs on my 2.0 JTS as it sounds like it is very slightly off (to my ears).

I have found the following guide by Jug

"ok, lets assume you have the most common type, a digital meter with a mode selector knob. there will be several resistance modes, each designed for a different range.

the primary winding on a coil usually has a resistance of 2 ohms, so set the multimeter mode to 200. this is usally at the bottom mode dial, at approx 6 o'clock, but it depends on your multimeter.

the secondary winding on a coil usually has a resistance of 3-5k ohms, so set the multimeter mode to 20k. this is usally at the bottom left of the mode dial, at approx 7 or 8 o'clock, but it depends on your multimeter.

primary winding: disconnect each coil pack's connector and touch the multimeter's 2 terminals on the 2 pins of a coilpack, and make a note of the reading you get on the digital display. repeat for all 4 coils.

secondary winding: reomve the coil and measure resistance from the spring that the plug touches to one of the pins (try both, only 1 will give a reading)

a result of "0" or "err" or infinite or open circuit means the coil is faulty, if one is significantly different ot the others it means it is worn and should be replaced. "

but my Coil packs appear to have 4 pins and also how am I going to be able to measure resistance across the pack when there is no current running through it? (as the above suggests the connector is removed? (probably missing something blindingly obvious).

Thanks


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Old 30-11-09
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You dont need current flowing in a circuit to be able to measure the resistance... Best thing to do is to compare resistance readings between known functioning coils and ones which may be dodgy.
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Old 30-11-09
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Originally Posted by Alfa_Daryl View Post
You dont need current flowing in a circuit to be able to measure the resistance... Best thing to do is to compare resistance readings between known functioning coils and ones which may be dodgy.
Thanks, I really should have remember some of that from physics back in the day

Does it matter which of the 4 pins I choose? as Jug's guide seems to suggest there are only 2 pins.
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Old 30-11-09
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Different types of coils will have the pins located differently. You'll get two different resistance readings. So if pins 1+2 give you an open circuit, try 1+3 or 1+4. I'd guess at 1+2 and 3+4. Wont do any damage trying different combos once disconnected from the car.
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Old 30-11-09
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Looks like 1 + 2 were the trick, although I think the dial on my multimeter is a little stuffed as at the 200 setting, it just turns itself off

At 20k though, I got :-

Coil Pack 1- 581
" " 2- 568
" " 3- 556
" " 4- 552

I tried phase 2 of touching one connector on the plug end of the pack and the other end on 1 of the 4 pins (tried them all) at all the different resistance ratings with no joy.
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Old 30-11-09
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I have a bust one at home somewhere, interesting to see if it went pop completely or deteriorated and just has a low resistance reading.

Your meter is fine I reckon, just wouldnt read as it would be over range in that setting. I just use auto range on mine, not all have that though.
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Old 30-11-09
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Oh, and to follow up, usually it is coil pack number 1 that goes first, often because of spilt oil that wasnt cleaned up. (Located just beside oil filler cap after all).
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