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Old 02-04-2010, 01:16 AM   #1 (permalink)
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Does anyone know of an updated procedure for testing the coil packs for 2001 through 2003 2.5 L engines? According to my Haynes manual and an article I found on Endwrench, both primary windings in the coil pack should measure at just less than 1 ohm. However, Ive tested at least 4 different coil packs for these model years and all of them show an extremely high input resistance on each primary winding as if they are open circuits. All of these coil packs perform just fine. So did Subaru change the design of the coil packs?
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Old 02-04-2010, 06:13 AM   #2 (permalink)
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Off another suby site;

http://forums.nasioc.com/forums/show....php?p=1357642

Personally I've always checked them "Old school" by sticking a known good plug, ground the strap, crank the motor and watch the spark.

Not very technical but gives a definite result I can see and don't have to second guess whether I'm measuring resistance across the right terminals.
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Old 02-04-2010, 09:02 AM   #3 (permalink)
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Thanks for the response, but this test procedure indicates a primary coil resistance of less than 1 ohm. Even on a new coil pack, I measure an infinite resistance on the primary ... and the coil pack works fine.

Has anyone else had a similar experience? Does anyone have an updated procedure for testing the coil pack?
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Old 02-04-2010, 09:37 AM   #4 (permalink)
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This seems to be the procedure:

To check the ignition coil's primary resistance, with the ignition off, disconnect the three-terminal connector from the coil. Connect an ohmmeter across terminals 1 and 2. This will test the 1-2 coil pack. Next connect the ohmmeter across terminals 2 and 3. This will test the 3-4 coil pack. The resistance should be between 0.63 and 0.77 ohms.

To check the ignition coil's secondary resistance, connect an ohmmeter between the companion cylinder coil towers. First test cylinder numbers 1 and 2, then cylinders 3 and 4. The resistance should be between 10.4 and 15.6 k-ohms (?)

Are you checking the correct locations?
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Old 02-04-2010, 11:15 AM   #5 (permalink)
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The coil packs on my 2001 and 2003 are 4-terminal packs. The two primary coils are between pins 1 and 2 and pins 3 and 4. Using a digital multimeter to measure the resistance for each of these coils gives me an out-of-range indication. This means the resistance is higher than the meter will measure. So it acts as if there is an open circuit connection.

Does anyone know what's inside the coil pack? Maybe a diode or transistor switch on the primary side that has a threshold voltage high enough to prevent a normal resistance measurement?
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Old 02-05-2010, 08:09 AM   #6 (permalink)
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Not sure what the other pin is, a trigger possibly but, try this;
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Coil Pack Testing-coil.jpg  
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Old 01-04-2013, 04:18 PM   #7 (permalink)
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Bump

I get the same things as CO 97. Secondary resistance between 1+2, 3+4 is about 12 k ohms, normal is 10.8 - 14.7.

Primary is the same as CO 97's - lead 1+2 don't move the needle, neither does 2+4. He said new fine ones test like this too, so is the manual wrong or what?

I tested other combos too:

1+3 = 50 k ohms
1+4 = infinite, but moves the needle just a bit
2+3 = infinite
2+4 = infinite
3+4 = 3 ohms

any ideas what this means?
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Old 01-04-2013, 04:23 PM   #8 (permalink)
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Note that many of the cases where ignition problems were had - people eventually discovered that the device that sends the coil the charge was the issue not the actual coil - so keep that in mind. If your having suspect spark issues. Pretty rare to see coil failures with Subarus.
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Old 01-04-2013, 06:05 PM   #9 (permalink)
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On the MY2000+ (or roughly around then) there's no way to check the primary of the ignition coils in the coil pack.

The high voltage secondaries can be checked between the towers for cyl 1 and 2, and the towers for cyl, 3 and 4. As noted above, these should be in the 12 k Ohm range.

As shown in the attached diagram, the coil pack contains an integrated igniter circuit. The four connections at the electrical harness connector are 12V, ground, and two lines which carry trigger signals from the ECM. The 12 V and ground terminals can be measured (between them for a short), and between those two and the two trigger signal pins. All should have high resistance. (Some meters with a diode check range might show different resistances when the test probes are reversed.)

The earlier systems had a separate electronic igniter. With those, the high voltage secondaries, and the low voltage primaries (0.73 Ohms) of the coil could be checked at the terminals as shown above. With these, as subiesailor noted, the separate igniter has sometime been found to have failed.
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Old 01-04-2013, 10:22 PM   #10 (permalink)
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Thanks Plain OM that makes sense now. I'm pretty sure the coil is fine, because if I "catch it right" I can rev it up to 2,500-3,000 RPM for several minutes before it dies out. Sometimes it idles almost normally for a few minutes, then stumbles and dies again.
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