BIGPOPPATAP Posted March 13, 2014 Share Posted March 13, 2014 I have a 08 impreza 2.5i 188,000 miles. Lots of highway miles, I commute 150 miles a day. The check engine light came on yesterday, and the car started stuttering, mainly from accelerating from a stop, and sometimes when slowing down quickly. I stopped by O'riellys this morning and had the code tested. It read that cylinder 4 was misfiring. I Changed the spark plugs, hoping for an easy fix. Plug 4 was burnt on the tip. The cylinder next to it ( I don't remember which plug, the closest one to the front of the car on the driver side), had a plug that was covered in oil, though the plug was still in good shape. Afterwards the car ran well for a minute, though now it sputters and almost dies whenever I come to a stop. My buddy, a former full time mechanic (as in ten years ago), told me it was probably a blown head gasket. the online research I have done says it's a valve cover gasket, or the gasket at the end of the spark plug tube. Anyone have some good advice for a wanna be mechanic? Link to comment Share on other sites More sharing options...
Fairtax4me Posted March 13, 2014 Share Posted March 13, 2014 Oil on the outside of the plug is from a leaking valve cover gasket. This is very common, and a cheap and easy DIY fix. If there was just oil on the tip of the plug inside the engine, that could be a head gasket, or a more serious problem. Since the number 4 was burned on the end, that probably means the coil for number 4 is now burned out. Link to comment Share on other sites More sharing options...
BIGPOPPATAP Posted March 13, 2014 Author Share Posted March 13, 2014 Thanks so much Fairtax4me. Would the Valve cover gasket cause the sputtering? Or is that the ignition coil? Or something else? Link to comment Share on other sites More sharing options...
BIGPOPPATAP Posted March 13, 2014 Author Share Posted March 13, 2014 I'm not doubting your expertise, I'm just curious. If it's the valve cover gasket why does only one of the spark plugs have oil on it? Are they sealed separately? I'll be changing this myself, probably the most complex mechanical fix I have ever tried, so I would like to figure out as much as I can before I try. Link to comment Share on other sites More sharing options...
Fairtax4me Posted March 13, 2014 Share Posted March 13, 2014 Yes, each spark plug tube has its own seal. Generally when you catch the problem early you find one spark plug with a little bit of oil around it. When it gets really bad, both seals go bad and both spark plug tubes fill up to the top with oil. The oil in the spark plug tube can cause arcing of the spark through the oil and cause a misfire if there is enough oil in the tube. This can also fry the coil if not fixed. One problem leads to another leads to another leads to another. Make sure that the gasket set you buy has the spark plug tube seals, and the grommets for the bolts. Link to comment Share on other sites More sharing options...
tirod Posted March 13, 2014 Share Posted March 13, 2014 When pulling the valve cover don't distort the tubes, which are crimped into the head and non-replaceable. Meaning that if one is loose, the factory fix is a new head. Other makes don't do it that way, but they leak more often. If you have one bad plug, likely another is, too. You can pull them and check (no, not that easy,) since it has 188k on it they should be the second set nearing the end of their life. New plugs all around is indicated by mileage alone, don't scrimp or downgrade from the factory OEM type. Cheaper types of plugs tend to misfire more than OBD allows and it flags a code. Link to comment Share on other sites More sharing options...
BIGPOPPATAP Posted March 13, 2014 Author Share Posted March 13, 2014 When pulling the valve cover don't distort the tubes, which are crimped into the head and non-replaceable. Meaning that if one is loose, the factory fix is a new head. Other makes don't do it that way, but they leak more often. If you have one bad plug, likely another is, too. You can pull them and check (no, not that easy,) since it has 188k on it they should be the second set nearing the end of their life. New plugs all around is indicated by mileage alone, don't scrimp or downgrade from the factory OEM type. Cheaper types of plugs tend to misfire more than OBD allows and it flags a code. Is there anything special I need to consider so as not to distort the tubes? Or just be super carefull? Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted March 13, 2014 Share Posted March 13, 2014 any work done prior to this happening? did the car get a new timing belt 80K ago? Link to comment Share on other sites More sharing options...
BIGPOPPATAP Posted March 13, 2014 Author Share Posted March 13, 2014 Yes, it got a new timing belt at 95k. No other major work recently. Regular oil changes. Also, I had the transmission fluid flushed and changed a month ago. Also, I found out a might have made a major mistake. I switched from conventional oil to full synthetic and about 170k. My buddy said that that could actually cause a lot of damage. Is there any going back? Should I switch back to conventional? Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted March 13, 2014 Share Posted March 13, 2014 unlikely the synth will cause any problems. there are many theories on this but, not a lot of real 'data'. wondering about the IACV hose. Link to comment Share on other sites More sharing options...
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