2007 Legacy Misfires

[Edon]

Ahoy all,

I've been having some annoying misfires with my 2007 Legacy for the past year now. The issue usually arises after having left my car for several days without driving it. First, it has a hard time starting up, then has a really hard time idling. Sometimes the CEL will start blinking, sometimes it doesn't. I usually let it idle for a bit until it starts sounding better, and kick it into drive where instantly is starts having a really hard time. At worst, I can't accelerate past 5mph, at best, I can get moving ~15mph with audibly noticeable difficulty.

The last time it happened it ended up stalling after getting into drive.

I had the codes read off and it's cylinders 1 and 4 misfiring.

After letting it idle and/or holding the rpms up for awhile, it eventually starts running fine. I then reset the computer by taking off the battery leads for a bit, and I don't see any issues until the problem crops up again.

I've tried injector cleaner but I'm still getting the problem.

I'm thinking there might be an issues with the coils (a short maybe?) or some other issue with the coils, thoughts/ideas?

Edit: ~45K miles

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[J-Chow]

Any aftermarket intakes? If so, switch to hybrid. Have you changed your spark plugs plug wires or coil ignition ? Try that as well. Maybe o2 sensors need replacing or there's a loose vacuum line on your intake? Trying to think of other things at the moment but in class right now so.... Good luck.

[Edon]

Nah It's all stock.

I forgot to mention, the cold seems to exacerbate the issue. I don't recall having many issues over the summer.

I'll check into those things you mentioned for sure, thanks!

[yarrgh]

Check for oil in the spark plug tubes. Run it at night and see if you can see arcing inside the engine bay, spray some water from a spraybottle on the wires to see if that incites arcing.

[Edon]

Friday I drove it after a week of no driving and it was worst than it's been before. It wouldn't start for a good 15 minutes, then ran really rough for another 15 minutes.

I replaced the spark plugs today, 2 of them had few drops of oil on the rubber sleeve that covers the plugs (cylinders 1 and 2). I'm gonna give it a few days without driving it to see if that changed anything. The last codes I had read off said Cylinders 1, 3, and 4 misfires detected.

PS plugs on a boxer = annoying lol

[Edon]

So the next morning after replacing the spark plugs my CEL came back on. I was able to leave the car without driving it for ~4 days. It started up fine.

I got the new code read off and it is as follows:

P0240
Catalyst efficiency below threshold - bank 1

Probable cause
Rich A/F ratio
Ignition system malfunction
Faulty catalytic converter


The guy at autozone checked the fuel cap and mentioned he was looking for vacuum leaks.

Any ideas on where to look next? I'm happy to do research on my own, I just have no idea where to start =\.

[GEE-OTTO]

Not the fuel cap or the ignition system it is your sensors you need to check both the AFR (orange) and the Cat/Fueling Sensor (gray) to make sure the connector are secure and that they are snug in the bungs If that checks out let it throw the P0420 and drive to the dealer once they read the P0420 they will replace your cat under the emission equipment warranty free of charge. Sometimes the catalyst breaks down in large pieces and causes this problem.


IF you cat is clogged you have a upstream problem that is the source of that i.e. faulty rich or lean condition, bad injector or bad AFR sensor

[Edon]

Awesome, I'll check that out asap, thanks for the help!

[Edon]

So the problem comes again after a trouble free summer. I live in the Pacific Northwest (Portland, Oregon) and started getting problems again after the cold weather/rain set in and I didn't drive it for a week.

Now I can't get it moving faster than 5 mph. It's parked on a street aways away from my place. I've replaced the plugs and just tonight replaced the plug wires and still no luck. I'm probably going to try the coil, but am getting really frustrated with the problem. I still need to check those 2 sensors you told me about GEE-OTTO.

It's idling semi-ok now (still a little rough) but as soon as it gets about over 2000 rpms or so it starts losing all sorts of power and struggling to keep running (it doesn't get much over 2K ever).

Any other thoughts? Coworker thinks that it may be fuel related, pump or filter?

[yarrgh]

your misfires may have contributed to the cat getting clogged up, hence the low RPMs.

[Edon]

Had the cats inspected, the rear was replaced. The AFR and cat/fueling sensor are snug. Issue remains =\. At this point it seems like all my research is just guessing and replacing, I'm gonna bring it in today and I'll report back what the issue ended up being.

[RaceFaceXC]

Can you log the ecu? If so chk the coolant temp sensor reading. It may be way off causing crap fueling/timing. They are relatively cheap and fairly easy to replace

[Edon]

So fun issue. Front cat had degraded to the point it was completely blown out downstream into the rear cat, clogging it, causing mass amounts of back pressure, causing the misfires. Emissions warranty covers it luckily. Thanks for all the help guys!