01 Forester - Coil Pack failing diagnosis - Subaru Forester Owners Forum
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post #1 of 9 (permalink) Old 11-13-2010, 01:26 PM Thread Starter
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01 Forester - Coil Pack failing diagnosis

I've been working on my girlfriends 2001 Forester lately after a check engine light came on last month. I went and had the codes read and the P0303 code came up. I pulled the spark plugs and found all of them significantly worn. The gap was more than double the specification. I replaced all four with Bosch platinums and correctly gapped them. I had the CEL codes cleared and didn't have the light come on for 3 weeks. It just came back on last week so I started looking into this issue again. I'm fairly certain the code is the same but I will confirm that this weekend.

After reading some other posts on this forum about miss-fires and P030x codes, I wiggled the wires to each plug as well as the wires to each injector with no significant change in engine performance.

I then decided to check the coil pack by using a timing light hooked up to each wire. What I found was that on cylinders 1 and 3, about every 6 to 8 revolutions, there would be a miss (no spark fire). The #2 cylinder was consistent and the #4 had excessive firing (2 to 3 times per revolution every 6 or 8 revolutions). From these results I'm looking at the coil pack as being the failure.

Can anyone else confirm this as the reason for miss-fire? Or am I overlooking something else that would cause this erratic firing order. I just want to be more certain before I drop the $$ on a new coil pack.
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post #2 of 9 (permalink) Old 11-13-2010, 01:32 PM
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I see this is your forst post, so welcome to the forum from Oregon!

Make sure the coil pack wiring plug connections are not corroded. If the connections are not clean & shiny, clean them & coat with dielectric grease. The high voltage cables should also be coated on both ends with dielectric grease, of course after checking & cleaned off any corrosion.

When were the spark plug wires last changed? If the spark plugs were in bad shape, my guess would be it's time for new wires.

Bobby...

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post #3 of 9 (permalink) Old 11-13-2010, 04:01 PM Thread Starter
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Hi Bobby,

Thank you for the welcome!

I checked the 4 pin connection at the coil pack and all pins looked shiny and not corroded. The spark plug wire age is unknown. However, there was dielectric grease on both ends of each wire. The electrodes on the coil pack were also shiny and there aren't any signs of arcing or other excessive mechanical wear.

I can easily replace the wires, but I still wonder how that would account for the inconsistent firing, especially on cylinder #4 (when it fires more than once per revolution). My plan was to replace wires and the ignition coil pack, but I could start with just wires and see if anything improves.

I'm a little more old school and used to working on engines with a distribuitor instead of the electronically controlled 'pack'. Seeing more than 1 pulse per cylinder per revolution seems strange to me.
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post #4 of 9 (permalink) Old 11-13-2010, 04:50 PM
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Does this help from End Wrench:

All late model Subaru four cylinder engines employ a
“waste spark” ignition system. Each time the ignition coil
fires, it provides a spark to two cylinders at exactly the
same time. Since only one of the two cylinders is on the
compression stroke when the coil fires, the spark to the
second cylinder (which is on the exhaust stroke) is “wasted.”"

Also: http://www.northursalia.com/techdocs...l/ignition.pdf

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post #5 of 9 (permalink) Old 11-14-2010, 08:09 AM Thread Starter
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Hi Kevin,

Thank you for the information and link to the ignition document. The waste spark is good to know about and honestly when I said I thought there was 1 fire per revolution it was based on the assumption that there wasn't any kind of 'waste spark' (although it does hold true since these are 4 stroke engines, 1 fire per revolution). These coil packs remind me of the coils on twin motorcycles.

So I read the 4 page PDF and the most compelling justification for a coil pack failure was best said in the document:
"For example, a coil that is beginning
to develop a defect could have no noticeable effect on engine performance
at idle when the running compression pressures are low, but will cause a
cylinder misfire under acceleration when cylinder pressures are high.
Higher engine speeds increase the likelihood of misfire because there is
less time for the coil to build up its electromagnetic field."
These symptoms are exactly what I experience with the vehicle. At idle, especially under load (accessories running, heater, lights), it stumbles and misses. It feels like the engine is about to stall out. Under acceleration load the vehicle again does not have a smooth/consistent rpm increase... it jumps all over until the engine is unloaded at a cruising speed.

For today, I'm getting some new wires and checking the codes again (still don't have my own OBD tool). I'm also thinking about hitting the pull and pay to find anoter coil pack. I found they have a 2000 Impreza outback sport. From the little research I have done, I believe this Impreza should use the same coil pack. Picking up the coil pack would only be $25 and I could return it if it also had problems.
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post #6 of 9 (permalink) Old 11-29-2010, 09:05 PM
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How did it go?

Noob here, so glad to find this thread.

My '01 had the same issues. Pepboy's wanted $775 to replace plugs, wires, and coil. I did all 4 wires and plugs for cyl 1 & 2. ( I'll get 3 & 4 soon when i have time and daylight. Cyl 2 was throwing the code anyway.) No check engine light, but runs a bit rough. Did you end up replacing the coil? If so did your car run better?

Experts: Are there any timing concerns for the coil? I am having a hard time separating my mind from the distributer concept. Is it really as simple as making sure the wires are in the proper place?! Pepboys wanted $140 for labor on this part. Am I missing something!

Troy
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post #7 of 9 (permalink) Old 01-04-2011, 02:39 PM
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Hi all, I have an 2002 2.0 litre non turbo with £112,000 mls and am about to bite the bullet with a new coil pack (£175.00). Actually I’m picking up a used part first (£45.00) just in case diagnosis is wrong.
Symptoms are intermittent; Initially 1 in 6 outings would result in misfire from cold but after 10-15 mins this would usually clear. As time has gone by problem has got worse and now 1 in 3 journeys has symptoms, misfire takes longer to clear when it occurs. On occasions I can stop, then start again and it clears. It ranges from fairly mild and quite hard to detect to ridiculous kangarooing and has almost cut out completely on a few occasions. Seems worse under load. Took in to local garage, where they re-gapped plugs, changed leads. Problem still occurs. Other day engine management light came on whilst misfiring. Took back to garage where from readings they traced it to cylinder 4. Changed plug on 4 but reckons coil pack is problem, and symptoms still there so I hope he’s correct. Is it worth trying dielectric grease on connections first? Anyone else had similar problems? Will be getting coil pack shortly so will keep you informed.
Note: timing belt replaced recently, could there be a connection there?

Note II: sorry, I think this may be in the wrong section, I’m a 2.0 litre non-turbo but just traced this coil pack problem so posted here

Last edited by rupert the bare; 01-05-2011 at 01:39 AM. Reason: poor smelling and possible wrong forum
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post #8 of 9 (permalink) Old 01-16-2011, 11:58 AM
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continued

Hi again,

Have now replaced coil pack with used unit and misfire problem still there. I thought it had cleared as first 2 outings ok as the car ran a dream with one or two minor misfires. Having done a 35 mile roundtrip today with the misfire there constantly, sometimes bad other times barley detectable (did clear briefly after stop and re-start) but car still driveable, I am now considering where to go next?

Could this be a mechanical or fuel delivery problem ? Itís quite odd as itís so intermittent

Any tips or ideas or similar stories folks?
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post #9 of 9 (permalink) Old 01-17-2011, 06:22 AM
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Quote:
Originally Posted by al_xv View Post
So I read the 4 page PDF and the most compelling justification for a coil pack failure was best said in the document:
"For example, a coil that is beginning
to develop a defect could have no noticeable effect on engine performance
at idle when the running compression pressures are low, but will cause a
cylinder misfire under acceleration when cylinder pressures are high.
Higher engine speeds increase the likelihood of misfire because there is
less time for the coil to build up its electromagnetic field."
I know it's a completely different coil setup, but my FXT had a coil pack (XT's are coil-on-plug) start to go bad. It would only misfire when the engine was under boost.
If you can find somebody with a working coil, you should try swapping just to see if the problem goes away. That way you can save yourself from replacing it when in case that isn't the problem.

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