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Old 22-09-2014   #1
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46777288 Ignition Coil resistance test

Hi
does anyone have any idea what the resistance reading should be for a 46777288 ignition coil from a 1.4 Stilo?

I was testing mine the other day as I think one of them is faulty and the LT side is reading around 0.7 ohms but the HT side is reading anywhere between 17 megaohms to over 20 mega-ohms (before you ask, yes that is Mega-Ohms as in 17,000,000 ohms, my multi meter tops out at 20 mega-ohms).

I've tried a number of threads both on here and elsewhere but can't find any good info on what the reading should be. I did find an article from Beru that says that on a double, off plug coil the reading on the HT side should be somewhere in the 6.8 to 7.8 kilo-ohm so being in the mega-ohms doesn't seem good.

Many thanks in advance
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Old 23-09-2014   #2
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Re: 46777288 Ignition Coil resistance test

If your engine still starts and somewhat runs you can measure all the coils and see what most of them are reading and can use that as a known good with a +/- 10%-15% error.

FIY: a resistance check is not good enough to determine is a coil is good or bad, because even if the resistance check is ok, the coil can still be faulty and that would only be apparent under load.

The best way to check a coil is with a oscilloscope. If you want to know more on the matter search for "ScannerDanner" on youtube; He has a lot of interesting and helpful videos on car diagnostics; videos where he shows how to find the cause of different problems. There are also quite a few videos where he talks about testing different coils .. you can get a better idea.

Hope this helps in some way
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Old 23-09-2014   #3
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Re: 46777288 Ignition Coil resistance test

ah another follower of scanner danner.
the fact you've delved in as far as you have testing them out youl love his vids.
with no test equipment like scopes etc maybe even a test light from coil wire to ground and watch the spark length and colour he does fairly frequently.
as stated above coils seem to break down under heat and load, even coil wires may test o.k with a multimeter but not carry a good current to the plug(judging by his videos).
https://www.youtube.com/user/Scanner...=ignition+coil

and heres one using a cheap ish oscilloscope
I love that paddle probe !

and when you've watched enough of his videos youll know what this means , but is this a valid test people ! I think so.
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Old 24-09-2014   #4
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Re: 46777288 Ignition Coil resistance test

Quote Originally Posted by General Disarray View Post
Hi
does anyone have any idea what the resistance reading should be for a 46777288 ignition coil from a 1.4 Stilo?

I was testing mine the other day as I think one of them is faulty and the LT side is reading around 0.7 ohms but the HT side is reading anywhere between 17 megaohms to over 20 mega-ohms (before you ask, yes that is Mega-Ohms as in 17,000,000 ohms, my multi meter tops out at 20 mega-ohms).

I've tried a number of threads both on here and elsewhere but can't find any good info on what the reading should be. I did find an article from Beru that says that on a double, off plug coil the reading on the HT side should be somewhere in the 6.8 to 7.8 kilo-ohm so being in the mega-ohms doesn't seem good.

Many thanks in advance
If there's a Mega Ohm reading then this means the coil is open somewhere. An open coil could still work if the opening is small enough for the spark to cross.

However, you should really double check your way of measuring. A normal multimeter, especially the cheap ones, aren't very reliable usually. As you're measuring resistance with a low voltage.

An actual Megger uses around 500V, depending on the installation that needs to be tested.
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Old 24-09-2014   #5
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Re: 46777288 Ignition Coil resistance test

Thanks to all of you.
Yeah I used a Uni-T meter which has been fairly accurate in the past. In the end I decided to order 4 new ones so should have them Friday so I can stick em in at the weekend.
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