disconnect battery to change ignition coil? - Subaru Forester Owners Forum
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post #1 of 9 (permalink) Old 05-07-2008, 07:13 AM Thread Starter
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disconnect battery to change ignition coil?

i'm going to swap out ignition coils later today. is it necessary to disconnect the battery when doing this?

thanks!
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post #2 of 9 (permalink) Old 05-07-2008, 08:18 AM
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It couldn't hurt to disconnect the battery, but IMO it's not necessary. If the ignition is off, there shouldn't be any power being applied to the coil pack. Besides, once you unplug it, it's not going to be connected to any power...

Bobby...

'07 FSXT - COBB Surgeline dyno Protune - Stage 1+
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post #3 of 9 (permalink) Old 05-07-2008, 08:49 AM
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but it might make it easier to reach the coil pack depending on your size... removing the entire battery that is..

05 XS
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post #4 of 9 (permalink) Old 05-07-2008, 11:14 AM Thread Starter
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ok great, i just swapped it out.

when i started the engine (the car has been sitting for a few days waiting for the coil to arrive) it gave a really rough idle, but after a minute it started evening out and seems to run like it is supposed to.

but i popped the hood afterwards, for visual confirmation / inspection, and i hear a tick / click noise every few seconds. it may have been there before, but i just noticed it now.

normal? thoughts?

i am about to go to monroe to get the CEL cleared and see what happens.

thanks!
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post #5 of 9 (permalink) Old 05-07-2008, 11:54 AM
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Did you end up disconnecting the battery? This can reset the computer and result in a few rough starts, sometimes very rough, till it relearns things.

2003 XS Premium MT >200k miles! ● 2005 Impreza 2.5 RS MT ● Robin-Subaru Powered Generator
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post #6 of 9 (permalink) Old 05-07-2008, 12:31 PM Thread Starter
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no, i did not disconnect the battery at all.

so i got it reset and it seemed ok, but after just a minute or two of driving i felt the misfires again !! grr. but no CEL. i wasnt home, so i kept going.

after another 5 minutes the CEL showed up.

so i drove to AutoZone and had it scanned. the original Cyl3 misfire returned ... the P303 code or whatever.

when i originally brought it to monroe, he assured me it was a bad Ignition Coil. the Cyl3 pin on the coil had some black soot on it.

after checking these recent misfires, there is no soot on the Cyl3 pin so i guess it's not a problem with the coil.

wires/plugs right? the coil was way easy to swap, but how difficult are wires and plugs? should the battery be disconnected do to plugs and wires?

what tools would i need? i searched but couldnt find a DIY with photos to help.

oh, one more thing - the guy at AutoZone said i should try swapping the Cyl1 and Cyl3 wires .. that way if the misfire started showing up on Cyl1, we'd know it's the wires. I dont know if that's such a good idea with a boxer engine.. ??

thanks guys!!!
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post #7 of 9 (permalink) Old 05-07-2008, 08:00 PM
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Well, a coil won't cause misfiring in an engine. The only thing that it will do is keep it from running, period. If the engine is misfiring, it can be just a few things.

The first obvious things to check are your spark plugs and wires. Make sure that the wires are connected tight and check the wires for any cracking.

The next thing that might cause it to misfire is engine timing. How many miles are on the car? is is turbo or N/A? The timing belt needs to be serviced at 100k miles. If it has a lot of miles and it is a N/A engine, than the timing belt will need to be replaced. I think that the N/A engines used a rubber timing belt that had teeth while the turbo engines used a chain (similar to a bicycle chain). When you replace it, there are arrows that you have to align. They are kinda tricky to replace and are dependent on getting the timing perfect. If you think it may be too difficult, take it to your dealer for service.

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post #8 of 9 (permalink) Old 05-07-2008, 08:06 PM Thread Starter
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yeah word, sorry .. what a rookie move of me to not leave my info..

2001 forester L , 55k , stickshift , way stock / no mods.

i dont think it's the belt... i'm pretty sure it's the wires or plugs. or both
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post #9 of 9 (permalink) Old 05-09-2008, 07:18 AM
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Well then it sounds like luck is on your side. With that few of miles, I doubt that it would be your timing belt. I know that it is STRONGLY recommended that the timing belt replaced at approx 100k miles. If it does happen to break, it can cause catastrophic engine damage. (Piston on valve, not pretty.) I had that happen to my '93 Civic Del Sol and after it broke, the engine was toast. The sucky thing was that I was going to replace it that coming weekend. Since you don't seem to drive your Forester much, I think that the age of the belt may start to become an issue, since it is now 7 years old.

All it will take for you to get it running smoothly is a tune-up kit with new plugs and wires, and an hour's worth of elbow grease!

'06 XT w/ 5MT
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