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 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

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/ScannerDanner/search?query=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.

General Disarray said:

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

Click to expand...

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.

Thanks to all of you. :slayer:
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.

currently in process of replacing/testing my coils (Stilo 1.6)

Had P0204 and sometimes P0203 while cold and more likely at more throttle.

Swapped coil #4 to plug #1 and it just ran on 3 cylinders with a different code but still ignition on #1 type code.
Swapping the coil back to plug #4 fixed the 3 cylinder issue, though cold starts remained an issue. I'm not sure what the ECU was doing to help the failing coilpack, but it must have been doing something.
When I get a working amp clamp for my oscilloscope I'll retest them all again.

Ordered a replacement coil and it tested at ~1.3MegaOhm between pin 2 and the plug connection. My other 3 all tested above the meter's maximimum (2 MegaOhms). All 5 tested around 0.5 to 0.7 Ohm between pins 1 and 3.

Replaced the coil-pack that was on #4 ....fixed the issue 95%. Occassionally I'll get a P0203.

So, I just ordered 3 more coil-packs from the same supplier on eBay. All 3 test 0.5Ohm low tension (pin 1 and 3), but on the HT side (pin 2 to spark-plug-connection) one tests 1345KOhm (1.345Mohm) one tests 1407KOhm, and the 3rd is out of range (>2000KOhm).

One of the "good" ones has some plastic broken so am returning that one, and I'll also swap the >2000KOhm one. I'd like to have 4 coils that measure similar to rule any differences out.

It should be noted that these readings were with a 9v meter. My 3v meter didn't give any readings for the HT side (set to 2000KOhm range) so I expect the voltage of the meter drastically affects the results here (backing up the comment that the 500v meter is the proper way to do this).
However, an amp clamp is a better investment for me personally, and should show more insight into what is happening.