Have a 99 OB 108k miles MT. Wife got a cyl 4 misfire code about a month ago. The plugs were changed at 60k but wires were original. Checked the wire at the #4 plug and sure enough it was corroded. Replaced the plugs and wires at about 106k miles.

 

After about 2 weeks the wife got the cyl 4 misfire code again. Funny thing is it happened at the exact same time and place as before. It happened on her way back from work about 5 miles from work just after being at 70mph on the the hwy for about 5 minutes.

 

I checked the wire and it was fine. Checked oil and coolant (head gasket??) and all looks fine. Reset the code.

 

A week later got the code again...same exact place. She drives about 40 miles each way to work and she never gets the light in the morning. Only in the afternoon on her way back to work and always at the same spot on the hwy. It's pretty level...no big hills. Car isn't driven while she's at work...only to and from work.

 

Anyway, I checked the wire again and the coil and all checks out ok. I took an oil sample last Monday but haven't got the results back yet. Car runs fine. CEL doesn't flash, it just comes on steady. I've never been in the car when the CEL comes on but I find it strange that it always comes on at the same geographic location (within 1 mile). EMI??

 

I'm always thinking of the head gaskets in the back of my mind but I don't see any symptoms (yet) except that possibly some coolant is leaking into #4 at high RPM and putting out the fire. But I've driven the Sube at 70MPH and no CEL.

 

Any ideas? I'm all out of them.

If you have MPFI you could try swapping the injector with another one. The problem may also be due to some carbon buildup in the cylinder so using a fuel additive may help there.

If you have MPFI you could try swapping the injector with another one. The problem may also be due to some carbon buildup in the cylinder so using a fuel additive may help there.

 

Good ideas. Thanks. I bought some Seafoam a couple of weeks ago and I forgot about it. I'll throw some in the fuel and into the intake this week and see if it helps.

 

As for the injectors...can you just swap them or do you need a new sealing washer or whatnot if you remove an injector (like in diesels)?

I think you can reuse the O-ring with no problem.

You might want to check that the EGR circuit is in good working order. Long shot, but the EGR feeds to the Cyl #4 intake runner. It seems to me that I've heard of others having misfire codes happen when the EGR is acting up. As I understand its workings, it only opens up on the highway, and it would be closing off as your wife slows from highway speed. Your car is also at that age where this circuit starts giving problems.

 

I dealt with a faulty EGR for about a year. I had to clear the code every 1 or 2 days. Once (but only once) I got a cyl #4 misfire. It has not happened again since I got the EGR problem resolved.

 

Commuter (97 OB)

You might want to check that the EGR circuit is in good working order. Long shot, but the EGR feeds to the Cyl #4 intake runner. It seems to me that I've heard of others having misfire codes happen when the EGR is acting up.

 

Hmmm...interesting. We did have an EGR code at about 55k miles and it was replaced promptly (by Subaru...I wasn't home at the time) and never had another EGR code.

 

How long do these EGRs usually last? It may be worth a shot since they aren't too expensive (I think).

 

Ahh...I miss the days of non-computerized engines...so sayeth the Luddite.

That happens to be the cylinder in pulloff's '99 that is toast. We haven't pulled the engine yet but I am guessing it's a burnt exhaust valve. I wonder if the EGR causes faster valve seat wear in #4.

 

You may want to do a compression test.

 

Have the valves ever been adjusted?

 

http://www.ultimatesubaru.org/forum/showthread.php?t=26776

You may want to do a compression test.

 

Have the valves ever been adjusted?

 

Haven't done the valves. It doesn't look fun with the horizontal engine. I was planning on doing the valves and valve cover gaskets this summer (assuming I don't have a HG issue). I should have done a compression check when I did the plugs but didn't think about it. Those little buggers are hard to get to but maybe I'll do that one of these weekends when it's not pouring out.

 

I put some Seafoam in the fuel tank but I want to put some through the intake system...do you usually pour it in or suck it in with vacuum? Is their a convenient location? Maybe PCV or some other vacuum line?

do you usually pour it in or suck it in with vacuum? Is their a convenient location? Maybe PCV or some other vacuum line?

 

http://www.ultimatesubaru.org/forum/showthread.php?t=23344

http://www.ultimatesubaru.org/forum/showthread.php?t=23344

 

Thanks...informative post.

 

BTW...this forum (along with "The Diesel Stop") is one of the best ones I've used. Quick and informative responses with minimal BS. Thanks for all the help!