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Discussion Starter #1
Hello new to community. We have had Subaru’s for over 20 years now. Our 2010 forester had thrown a mis fire cylinder 4 code. We changed plugs and wires check engine light is gone but car is running very badly. First no check engine light now, can’t rev past 4000rpm in park or neutral, slow take off, not shifting right, we hear a slight whooshing noise when driving. Shifting 1-2 are very slow at right rpm but 3-4 tac to 4500 then shift. Can’t seem to get to 50. Transmission fuel is full,clean, and no smells. Thanks for any info we are at a loss. If you need more info I will do my best to answer.
 

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Silly I know but there aren't vacuum pipes unplugged, air box tight? Any whooshing shouts air to me? plugs gapped right, caps on tightly (I would think they are as no mil light).
 

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Discussion Starter #3
We were thinking vacuum also but every one we checked seemed good. When idling car seems perfectly fine. Thought I could hear a slight psst noise when idling but can’t put a finger on it. Plug gaps good and wires are right.
 

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Strange it's only started since you've done the plugs, I assume these are new problems to the misfire you had before? Makes me think something's been disturbed whilst working.
 

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And... I gotta ask... Did you put the new wires in the same order as the old ones? (as in: did you by accident switch 2 and 4, or 1 and 3?)
 

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Discussion Starter #7
Strange it's only started since you've done the plugs, I assume these are new problems to the misfire you had before? Makes me think something's been disturbed whilst working.
Yes new since doing the tune up. Plugs were only in finger tight. Double checked air filter to make sure it was put back right.
 

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I wonder if you have a bad plug, or bad plug wire.

You could disconnect one plug wire at a time from the coil. WARNING: Only connect/disconnect while engine is NOT running.

If you discover that unplugging one of the wires doesn't make it worse, you've found a possible culprit. Try replacing the wire with one of your old ones, same with the plug...
I've seen brand new wires that were not assembled right and the clip that is supposed to connect to the end of the spark-plug is bent, buried inside the boot on an angle or simply damaged.
 

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Discussion Starter #10
I wonder if you have a bad plug, or bad plug wire.

You could disconnect one plug wire at a time from the coil. WARNING: Only connect/disconnect while engine is NOT running.

If you discover that unplugging one of the wires doesn't make it worse, you've found a possible culprit. Try replacing the wire with one of your old ones, same with the plug...
I've seen brand new wires that were not assembled right and the clip that is supposed to connect to the end of the spark-plug is bent, buried inside the boot on an angle or simply damaged.
Could it be coil pack even if no check engine light. Only driven car maybe 3 miles since acting this way? Still not sure about the noise.
 

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Discussion Starter #13
Thank you all for the advice. We changed coil pack and car is running great right now. Only gone a couple miles but can tac past 4 in park, shifts good sounds nice and smooth. Whooshing noise may have been air filter not put back in quite right first time because noise is gone also.
 

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Discussion Starter #14
So right after car was running great we went through a puddle an now car is running like crap. Cylinder 4 wire keeps popping off. Code reader says cat failure but we have never had that stinky egg smell. We still can hear air coming from somewhere. Shifting is still very slow at takeoff. We are again at a loss.
 

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Discussion Starter #16
Hi all. Had a tread earlier where we did a tune up. The car is a 2010 Subaru Forester non turbo 2.5, sport shift. Car ran great after plugs, wires, and coil pack done. Drove through a huge puddle ( unavoidable) now car is worse then before. Bought a code reader one time it says p0420, mis fire 4. Check plug and wire. Wire had piped off s little. Cleared the code then reread now mis fire 1,2 and p0113,po102.. oh we also changed alternator. Thought we had bad coil pack exchanged it, put another new set of wires. We are at a loss every time we clear codes and start car something else pops up and not the same codes. Also just started getting a howling noise that’s why we changed alt.
 

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2009 Legacy
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P0420 is "Catalytic Converter Efficiency Below ", a failure that may not be associated by a smell.
The other codes are indeed misfire codes.

It is hard to imagine riding through just a puddle would have directly affected your ignition. Those wires and coil pack(s) are way up in the engine compartment unless you drove that thing into the Long Island surf.
If I were you, I'd spray some contact cleaner into the O2 sensor connectors. Maybe moisture got in there and is creating havoc with the system.

Your 2010 has one coil pack or does each hole have a coil/wire? I forget.
In either case:

If it has a wire from that one coil pack to a spark plug and that wire keeps popping off, I suspect you don't have a good seal on the spark plug, it is loose or there's something wrong with that plug. Knowing how much fun it is to get tools in the spark plug hole, I'd just replace that one spark plug to eliminate it as a possibility. They are cheap.

If your car has an individual wire going to a individual coil in a hole and the wire keeps popping off, you have a bad mechanical hold down of that plug. Secure it better or just replace the thing.
 

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Discussion Starter #19
The puddle was quite large. It is an area on our road that kinda washes out every year from snow melting. We have just one coil pack. After changing the wires second time they have stopped popping off. We were wondering could a vacuum leak cause the p0420 code? Just running out of ideas. Never had this much of a problem after going through water. Had Subaru’s for over 20 years.
 

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Oh, I was under the impression the P0420 occurred after your drove through the puddle and then it started misfiring while the P0420 disappeared.
So you still have the P0420 code and misfires?

Sure, it could be a vacuum leak but if you've been driving around with a misfire, eventually it will affect the efficiency of the CAT. In your case, it may well indicate that your CAT is indeed bad.

Using a non-contact IR thermometer with a laser pointer, you could see what the in and out temperature is on the actual pipes on the CAT. Out should be 100-200 degrees HOTTER than the inlet. So in other words, the end being fed by the engine is colder than what goes out the exhaust pipe.
That's really just the P0420 code - it will pop back up, even with a new cat and sensors, if you don't fix your misfire, wreck your CAT again, etc. There's no parts canon big enough unless you fix the root cause - in your case, most likely that misfire.
 
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