Fuel injection O-ring replacement, what else while I'm in there?

[toyhawk88]

Short question: will replacing the fuel injector O-ring fix a misfire. If this is a good idea to try, what else should be done while they're in there?

Background: 2002 3.5 Pathfinder LE
1. my check engine light has been on and off (mostly on) for the last year. they replaced all four O2 sensors when the CEL problem initially appeared.
2. The situation became critical two days ago when my 2002 Pathy started misfiring and my CEL started FLASHING! The shop ran a diagnostic and pulled multiple codes including a cylinder 4 misfire and the dreaded 420 and 430. But they didn't really believe the cats were clogged (just probably inefficient), so they tried a simpler, cheaper fix first: replacement of ignition coil #4 (left side). They also replaced the corresponding spark plug (total about $370, including diagnostic fee). They drove it twice and said it ran great, but when I picked it up in the evening it was back to the same misfiring, possibly a bit worse.
3. I have read the other threads on the 420/430 code...and I appreciate that they are NOT jumping directly to replacing all four cats.
4. They are suggesting a $350 replacement of the fuel injector O-ring (2-3 hours labor, cheap part).They said there was some kind of tech alert about it.

Other thoughts/info:
-- I'm skeptical b/c it might not fix it AND I might STILL have to shell out $2400 for new cats after this. (If I go with cats, I'd really prefer if my regular garage did the work since they have the O2S history and because they are a small local shop of great guys that would probably only charge me $1800-2000(?).
-- I keep asking about the catalytic converters because the car has 226k miles on it with original engine and cats, but they're not convinced it's worth spending the $2400 on them right now b/c it might not solve the problem. Something could have fouled the cats, like...
-- Same time last year, I used this "nearer" shop for another last minute emergency prior to traveling for Thanksgiving and they did a tune up along with a valve cover replacement--a whole 'nother story since they used the wrong one initially, come to find out Nissan redesigned it. I only drove 900 miles on the WRONG one, leaking and burning oil! They did their best to make it right, but I now read that many folks have had problems with the valve cover issue clogging their cats... Immediately after that replacement issue, I dropped from 16 mpg to 14. Throughout this year it has waivered between 13.5 and 15.5 but the garage says it's not related. But it was clearly a before:after case.
-- Right before the car started acting up two days ago, we filled up the gas tank. Could bad gas have set off a serious of unfortunate events?

I'm really counting on you all to give me some guidance here. My Pathfinder has been very good to me. ONly new car I ever had and it's been a reliable, economic beast for 13 years. It still has most everything original except for standard maintenance items. I couldn't be happier with it and want to keep it as long as I can. Please respond in plain language because I am not very knowledgeable about automotive terminology, though I am learning more every day! Thank you! --Dawn

[atraudes]

Hi Dawn,

First off, don't get the o-rings replaced without getting some more information. A really bad vacuum leak could cause a misfire, but based on what else you've described, it wouldn't be my first target. What was their reasoning for wanting to replace the o-rings? Specifically, what was the tech alert? I haven't heard about any chronic problems with them around here. It sounds a little shady to me. However, if you do end up having them replaced, have them put a new PCV valve in. They run about $5 and are otherwise a pain in the butt to get to. Having the injectors flow tested and/or cleaned is also food for thought. I mailed mine off and had it done for about $100. It'd be more peace of mind.

In response to your other question, I doubt bad gas alone could have triggered all of this, though I suppose it's possible.

Unless the catalytic converters are completely clogged (not likely if you've only had this problem for the past year) they're not contributing to the primary problems you're addressing. Some people here simply live with those codes citing no side effects, so get everything else addressed before you decide to focus on them. I had the 420 and 430 codes when I first bought mine as well and after replacing the upstream catalytic converters they went away (~$1200, btw, $400 for Walker 16344 and 16343 from Amazon, plus $800 labor). However, catalytic converters don't generally just go bad on their own; they go bad because of rich fuel conditions (too much fuel in the cylinder).

The valve cover gaskets are all squared away now, though, right? They're not leaking oil or anything? I've never heard of valve cover gaskets causing catalytic converter problems If they're all taken care of now, I'd put it out of mind. It's possible they damaged the ignition coil while replacing the gasket, but it could have just been a coincidence.

What I'd recommend first is going to your local parts store (O'Reilly, Napa, Advance, Pep Boys, whathaveyou) and have them pull the codes your computer is throwing (they'll do it free of charge). You'll get the 420 and 430 codes naturally, but I'm curious if any others are being thrown. Your next best action is really contingent on that information.

Good luck!