Adam Posted May 8, 2010 Share Posted May 8, 2010 Just replaced my O2 sensor, and the gasket that goes before it(which coincidentally blew out again... High quality stuff O'Reillys!), but I'm still getting a misfire... It's only misfiring below 2krpms, above 2k power is great, it runs great, does highway really well, but accelerating from a stop is a little dicey... Now the kicker... When the O2 sensor is disconnected, it runs so much better, it gets off the line quite well, but still has a rather random misfire... When the O2 sensor is connected, it sounds like the misfire is consistent, not random. I've replaced every piece of the ignition besides the distributor cap and the actual distributor, so that'd include plugs, wires, coil, ignitor, rotor. Plugs are all gapped consistently, I believe at .026 is where they were gapped stock(Bosch Platinums). Fuel filter was changed, timing belt(and the alignment marks all lined up with their corresponding dimples). With the O2 sensor, and the new gasket, backfiring stopped, so I think it's close to passing emissions now, but this stumble is driving me nuts... Distributor cap? Crank angle sensor? I'm at a loss, and I've got no codes... Link to comment Share on other sites More sharing options...
jj big shoe Posted May 8, 2010 Share Posted May 8, 2010 Did your truck sit for a while or something? I ask because mine sat for about a year while I was working on it. I started it and ran it out of the garage regularly but never drove it any real distance in that year. Once I got it on the road I had an occasional sputter and hesitation for prolly 500-800 miles, pretty random. Thats a few tanks of gas and a few bottles of injector cleaner, too. I'm guessing there was some gunk in the fuel system that took a good while to clear since the sputter went away on its own. Just replaced my O2 sensor, and the gasket that goes before it(which coincidentally blew out again... Any chance your cat is clogged up? Link to comment Share on other sites More sharing options...
Cuong Nguyen Posted May 8, 2010 Share Posted May 8, 2010 What air filter are you running? It's possibly that your mass air flow sensor could be dirty. Check to see if the connections are clean and not corroded. Link to comment Share on other sites More sharing options...
Dowser Posted May 8, 2010 Share Posted May 8, 2010 I've heard others here say to stick to NGK plugs as well claiming the Bosch's gave them a little trouble until they switched back. Might be something to look into. Link to comment Share on other sites More sharing options...
Adam Posted May 9, 2010 Author Share Posted May 9, 2010 (edited) MAF sensor was cleaned. Another tidbit of info, my MAF is bored .125" over, never had an issue with it before, so I'm going to keep assuming that it isn't MAF related. Air filter is a Krap 'n Nasty... Yes, the truck sat for 2 years, but I replaced the fuel filter, the fuel rails, and the pump is pumping quite fine. It's also already gone through 3 tanks of gas now... Also, if it were gunk in the system, the engine would poorly all the time, not just when the O2 sensor is plugged in... The I just got done replacing the gasket again after wrestling with a stripped exhaust screw, and I find out that the gasket still doesn't seal... I put a pair of vice grips on it for now, but it seems like it's also not sealing at the top of the flange... I'm not sure what to do about this... Maybe bend the tabs for the flange so the middle seats better? It's still running pretty rough, until past 2krpm, then it's as close to a rocket as a Pathfinder can get I think the gasket issue is what's causing a lot of the problems with the O2 sensor, since it obviously can't get a proper reading if the exhaust is exiting before it gets to the O2 sensor... Edited May 9, 2010 by Adam Link to comment Share on other sites More sharing options...
Cuong Nguyen Posted May 9, 2010 Share Posted May 9, 2010 The o2 sensor should not have that much of an effect as to the rough running. Either it's bad ignition timing, or crappy plugs and/or wires. I'm still using the stock wires and I have well over 200k miles with no problems. Running Regular NGK plugs. Link to comment Share on other sites More sharing options...
Adam Posted May 9, 2010 Author Share Posted May 9, 2010 I don't think its wires or plugs... the quality of the duralast wires seems pretty high. I still have the originals, but they were arcing to the cylinder head. The old plugs were platinum +2's, still have those around, and they ran great before the parking, so I didn't throw them out just in case... I'm gonna get a new cap next payday or when my tax return comes in, but I'm looking for any other suggestions... Link to comment Share on other sites More sharing options...
adamzan Posted May 9, 2010 Share Posted May 9, 2010 (edited) Could be partially plugged cat as my fathers r50 is doing the same. Stumbles when you take off but runs fine above a certain rpm. Also I had a really hard time getting it to pass emissions the second time as well. Edited May 9, 2010 by adamzan Link to comment Share on other sites More sharing options...
Adam Posted May 9, 2010 Author Share Posted May 9, 2010 Could be partially plugged cat as my fathers r50 is doing the same. Stumbles when you take off but runs fine above a certain rpm. Also I had a really hard time getting it to pass emissions the second time as well. I'm also wondering about this, if that's not potentially the reason why it's also popping the gasket, the path of least resistance... Link to comment Share on other sites More sharing options...
Kingman Posted May 9, 2010 Share Posted May 9, 2010 I would suspect a clogged cat. If at anytime it was overheated, it very likely could have melted down inside and is blocking exhaust flow. Running way too rich will kill one too. If the gasket keeps blowing then there's something blocking the exhaust so it's only way out is through that gasket. Try taking the cat off and see if it runs any better, it might be loud, but worth a shot. Link to comment Share on other sites More sharing options...
nismothunder Posted May 9, 2010 Share Posted May 9, 2010 My 95 is doing the samething right now with its v6.It wants to die when you stop so you have to give it gas.I had a miss but its since gone away. Link to comment Share on other sites More sharing options...
Adam Posted May 9, 2010 Author Share Posted May 9, 2010 Decided I might as well take care of it now, since it's one of the last things left, gonna replace the cat with a Magnaflow unit, 101 shipped isn't too much to spend on that. Pretty soon, I won't have anything left to do besides rebuild the engine Link to comment Share on other sites More sharing options...
Adam Posted May 19, 2010 Author Share Posted May 19, 2010 At the exhaust shop, they're gonna chop out the flange that leaks and weld a new section of pipe in... the cat is getting replaced as well, the bolts holding it in were welded in, so I couldn't replace it myself. Hopefully this is the end of my saga... Link to comment Share on other sites More sharing options...
Adam Posted May 19, 2010 Author Share Posted May 19, 2010 That was a bust.... plug the o2 sensor back in and it runs worse than ever until 2k, then after 2k its a banshee... with the o2 unplugged it still runs rich but at least can accelerate off idle... Link to comment Share on other sites More sharing options...
Adam Posted May 19, 2010 Author Share Posted May 19, 2010 O2 sensor wasn't seated properly, fixed that and now it runs much better, though a little weak off the line, and if I'm coasting slowly and go to accelerate without kicking down, its really hesitant, and there's an audible sound, almost a clicking, like a relay or something... Link to comment Share on other sites More sharing options...
Adam Posted May 19, 2010 Author Share Posted May 19, 2010 Came home and timed it, its great now. Hopefully this means it can pass emissions too! Link to comment Share on other sites More sharing options...
Adam Posted May 26, 2010 Author Share Posted May 26, 2010 Bumping this up. I just took the emissions test, and my NOx is way out of spec on the 15mph, everything else is way way below spec, and everything else passed(though NOx on 25mph test only barely made it). Did some Googling, 2 things stuck out to me... EGR, which I haven't replaced yet, but I have a replacement ready to go in, and running lean. I'm most likely absolutely running lean, because I'm running a bored out MAF, .125 over, meaning I'm putting more air in while the sensor still thinks I'm putting the same amount in. The first thing I'm going to do right now though is replace the EGR, and if that does it, then I'll skip the MAF, but I can get the MAF for cheap at the junkyard, so no biggy... Any other suggestions to get the NOx down? Link to comment Share on other sites More sharing options...
Adam Posted May 27, 2010 Author Share Posted May 27, 2010 Well, I passed! I adjusted the TPS, brought it back, failed, they let me adjust the TPS again, adjusted it the other way, passed in training mode, then they ran the full test, and gave me my sticker! Link to comment Share on other sites More sharing options...
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