SUBA3

Hi,

I drive a Subaru Forester 2005. Since a few weeks, I get an error code "Misfire on Cylinder No. 3" which causes the Check Engine indication to come on and then the Cruise Control light comes on flashing. The four spark plugs have been changed for Platinum ones. I still get the problem. This problem always happen under high humidity conditions and resolve when humidity level goes down. Any idea what could be the problem ? Thank you.

ferret

In dark conditions, spritz a little water around the coil or wires. I suspect an insulation breakdown on one or the other. Both are know to cause misfires on N/A Subaru's.

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04XSPP(7 Subaru's since 1978 All 5 sp)ILuvSubaru's

SUBA3

Thank you Ferret for your suggestion.

I will do your test. If the problem occurs after your test is done, I will get the spark plug cables changed. Do you think this could solve the problem? When the codes were downloaded, the code for misfire on cylinder No. 3 came up but there was also a code for multiple misfires.

Any advantage in having changed the spark plugs for platinum ones? The mechanic who suggested and changed the spark plugs seemed convinced that this was worthed. I still doubt about this... These spark plugs costed 86 $ for the 4 of them...

Thank you for your comments.

Ciau!

neolynne

I'll lay bets on it being a cracked coil. Does it go away after you drive for a few miles? I had the same problem with my previous Foz (01) right down to the high humidity issue. On rainy or humid mornings it would initially run like crap (rough idle, erratic acceleration), the CEL would come on (no CL light on this MY) but after the engine warmed up it would run okay. Turned out to be a cracked coil (affecting #3 cylinder too. Mechanic told me that once the coil got warm it expanded enough to close the crack allowing the cylinder to fire properly.

SUBA3

Thanks for your comments Neolynne, greatly appreciated.

Yes, your description fits very close with mine. The CEL (which I assume is the CHECK ENGINE light) first comes on flashing and then stays on steady for 10-15 minutes I would say (I assume this is the time it takes to warm the coil, however, I never monitored exactly). Then the CRUISE light comes on flashing and for sure the cruise function is disabled during that time.

The CHECK ENGINE and CRUISE lights stay on steady for a couple of engine starts and then go off if humidity is at a normal/low level. Therefore this condition may last for a couple of days if I don't use my car.

A broken coil, is this a condition that could be detected easily (visually) by an experienced mechanic ? This leads me to the following also:

Does anyone know any good and reliable maintenance manual (including wiring diagrams or at least good schematics) for the Forester 2005 and how/where we could buy it/them ?

Thanks in advance.

(looks like this forum may also be quite useful to share experiences and find Forester's solutions)

bbottomley

A good way to see whether the cable might be at fault would be to swap it with the adjacent cylinder and see what happens. But I tend to agree with those suggesting a cracked coil, due to the intermittent nature of the problem and its tie to humidity and heat.

You did pay a lot for your platinum plugs. Prices on eBay (in the US anyway) are less than half of that, though you'll always pay a premium if you buy something as part of a professional maintenance job. Be assured, however, that the platinums will have a nice long life ahead of them.

The situation with the cruise control and light doesn't mean that anything is wrong with cruise control. It's simply Subaru's idea of a safety feature, to keep you driving cautiously and attentively during a time when the engine might not be able to deliver its customary performance.

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2003 XS Premium MT - 2005 Impreza 2.5 RS MT

subaru4me77

I agree with everyone on this post about it being a cracked coil. I have had a cracked coil before on a different vehicle (Jetta VR6) and had the same problems as you describe.

As ferret said, you can spray the coil with water. If the coil has a crack, you may see a spark when you spray it.....this will tell you where your problem is located.

SUBA3

Hi,

Thanks bbottomley and subaru4me77 for your respective reply.

I did the test previously suggested by spraying a bit of water on the coil and cables, and did not see any spark.

However, today, I was lucky to meet an awesome Subaru-specialist-mechanic who put a lot of logic in all this saga.

I hope to believe he found the clue. Anyhow, next weeks will talk as the upcoming fall-wet-weather is on it's way. However, his explanation and solution were very logical.

The experienced-mechanic uninstalled my car coil to inspect it for any damage. A small scratch was found probably caused by a previous spark (but nothing to worry about as it is so thin). However, he explained that on the new Subaru models, the coil has been moved and the way the cables are now connected to the coil make the plug(s) more susceptible to catch and trap humidity when engine is cold (and may explain why I never got the problem with my previous Subarus). That explains why the trouble is coming and going as the problem disappears when the engine gets warmer. The CHECK ENGINE and CRUISE indications disappear after a few engine starts, this is normal in the circumstances.

Therefore, he simply applied sealant (tube) at the junction of each of the four coil connections and related plug.

I would also like to add that I am so glad that my car problem has been looked at seriously and meticulously. This helps building this so-important-thrust between the car maintenance professionals and the customer. Cars are not an investment, we all agree. However, the thrusted professional relationship between the customer, the specialist-mechanic, and garage service department is.