CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

02 Subaru Impreza - Repeatedly ruined spark plugs and exhaust


Posts: 1

I have an '02 Subaru Impreza 2.5 TS (Manual Transmission). Recently it started running at low power, threatened to stall at low rpms (with normal-to-increased gas), and the exhaust got very loud. Check engine light was on. The exhaust sound pulsates at idle, and is coming from around the catalytic converter. Finally it almost didn’t run, and the check engine light started blinking.



I got the car checked out, and they found all spark plug wires were loose, and one was blown off of the plug. That plug was blackened and the ceramic was cracked. They replaced plugs and donut gaskets around the catalytic converter. The car has been running better for around 2 months, and now is beginning to have the same problems. Hesitation at starts, threatens to stall, very low power, and loud exhaust noise from around the catalytic converter (pulsating at idle). The car had this problem during winter, and now during summer months in Michigan. Most trips tend to be fairly short (10 - 45 minutes) city trips, with few highway trips of 45min - 1hr.



On a side note, the car for some time has had increased exhaust noise when you give it a decent amount of gas. It seems to be the last third of the gas pedal at any gear and any speed. There is a fairly defined point in the pedals range after which the exhaust gets noticeably louder. There was a little bit of decreased power, but other than that the car had been running great (This has been happening for around two years). I’m not sure if its related to the current problems, but I thought I would mention it.



2002 Subaru Impreza 2.5TS

2.5L H4 engine

140,000 miles

Ann Arbor, MI

I suggest you have the injectors looked at to see if one may be leaking. Also check the exhaust system for a air flow restriction. It may be good also to check the O2 sensors and the plugs to see how they are doing. Checking for any sign of trouble. I assume there isn’t a CEL light on currently. If there is it certainly needs to be followed up on.

Not currently. It was on a week or so briefly, but then turned off again. The engine code that the repair shop reported when the car was previously fixed is listed as P0302 for #2 misfire.

To me, it sounds like the exhaust mainfold gaskets may be leaking, and the hot exhaust gasses escaping through the leaks are cooking the spark plugs and boots. These are different gaskets than the catalytic converter donuts. These are right between the cylinder head and exhaust mainfold.

The appearance of the spark plugs can tell a lot about how the engine is running. Here are some excellent color photographs of different engine conditions on spark plugs, and, explanations of what caused the conditions: http://www.autolite.com/pdf/PlugTips.pdf Examination of your spark plugs can give you an idea of what the cause and remedy may be.

Thanks for the pictures and information! From the repair shops description it definitely sounds like detonation. Nothing else implied that the ceramic would be cracked. Thanks all for the advice, at least I have some things to check out now.