paul7002

Ok I've replaced the o2 sensor(messed up the original swapping it), new plugs, and new pcv vale. What I have is while at idle bank 2 reads about double than bank one. the o2 sensor on bank 2 is reading .8 - .9v while bank one is at .45v most of the time. Also, slight stumble when pressing the pedal at about 1K rps like a miss. I can almost hold it there with the brake on and make it stumble like crazy. It runs great either below or above that point. I don't have them in front of me but the fuel trims don't look right on bank two either. I did clean the throttle body some time ago so I'm a bit suspicious of it other than than I have no idea why it would run rich. I'm assuming a high reading from the o2 sensor is rich I hope that is correct. Also, no CEL is set but the gas mileage is awful and the exhaust smells bad. Could a throttle body being bad or something else cause it? I've read the FSM and I can get a fuel pressure gauge to check pressure and such but cannot do the testing from the FSM. What is everyone's opinion should I just bite the bullet here and take it to the stealership or? I've searched for exhaust leaks and vacuum leaks and haven't found any yet. It's really odd it's only on the one side. I know one thing for sure I want my Z back to normal this is driving me nuts!

samsniss350z

I wouldn't be inclined to take it to a Nissan stealership, I'd try to get recommendations of workshops near where you live by members of the forum who have used shops with a good reputation.

paul7002

That would work better. I'm located in NC in between Fayetteville and Raleigh so either direction would work. Anyone know of a decent repair shop that's good with Z's? My zip code is 28327 I'd be willing to drive a ways to get good reliable service at a good price. Anyone?

zakmartin

Did you replace the O2 sensor, spark plugs and PCV with OEM parts or aftermarket? Did you give the computer enough time to re-calibrate to the new parts?

paul7002

No but it has the same identical problem. The new o2 sensor is reading the same. There is one thing maybe I should check is to make sure the line voltage is good. I know the o2 sensors generate some but the .45v baseline should be there. After watching the fuel trim and comparing to bank 1 it doesnt look too different and the fact I have a stumble could maybe mean something else wrong with fuel or ignition. Oh what the heck I'll keep at it as long as it doesn't cost too much. Oh also, the plugs I installed are better than the stock plugs and I did get a boost from them as cyl 1 is leaking oil into the spark plug hole and needs a gasket change so I'll be doing that too. I was noticing though maybe it's too lean and not rich because I introduced air on the bad side and the o2 voltage went up not down. I couldnt find any leaks though it may need a smoke test or maybe Ive just got a stupid clogged injector. Ok its evident I dont have a clue here but maybe eventually something will turn up.

Italianjoe1

iTrader: (6)

Do you have all stock exhaust? I've seen these cars have issues with the gasket at the top of the test pipe, where it meets the header, drawing fresh air back in when idling and setting a false lean code. Runs perfectly otherwise as you said so that's something to check.

If you actually do have an a/f error then something is leaking air or fuel into the engine upstream, which would also cause the stumble if say that injector isn't closing down properly and it running that cyl too rich at idle but once the RPMS come up it's not enough to be out of line.

paul7002

I have all stock. I know I've searched for an exhaust leak with no luck. I even re-tightened the O2 sensor to make sure. It does feel exactly like you said as if it gets enough fuel when the rev's are higher or at least are hitting the sweet spot for it to fire. I sprayed cleaner all over the intake and lines searching for leaks by watching the fuel trim with no luck. I've even disconnected all the vacuum lines and plugged them off just to isolate any leaks no luck. If it were an exhaust leak I don't think it would stumble like it does. If I can I'll try to put a video together and show what it's doing. It's really quite simple it will not miss unless under a load and only misses at around 1k rpm. I can put my foot on the brake in gear and barely press the pedal and make it happen.

Italianjoe1

iTrader: (6)

Try holding the car at the point where it stumbles for a little bit, 30 seconds or so, and see if it sets any misfire codes. That may help you track down which specific cyl is the culprit. It's hard to meet the conditions for a misfire code to trigger though, so it may not set if it's something that is just causing a power balance issue and not a fully dead cylinder.

paul7002

Ok great... I held it there and it was hard to because the pedal has to be just right. I got code P300 in memory no MIL flashing or other. So random misfire is seems to be one of the harder ones to diagnose but I can say I saw the fuel trim on bank to going nuts when it was missing going from 8% all the way to 16% and at one rime 25% max. It seemed to fluctuate with the engine stumbling. So it's doing it at about 800 RPM. I first noticed the miss after cleaning the throttle bodies(didn't remove them), and changing air filters. The car started stumbling then. Since then I've cleaned MAF's, swapped MAF's, changed MAF's(used from Ebay) changed the O2 sensor Bank 2, changed spark plugs, and the PCV valve. No change. Then removed both throttle bodies and cleaned with no change still stumbles. I a suspicious of the TB on bank 2 but not even sure where to start. Most things I've read point to electrical so I guess I'l start there and check connections but this is not a constant problem so I don't think that makes sense for me. It seems to do with A/F mixture somehow.

myfirstzcar

Swap the throttle bodies and see if the problem goes to the other bank. Otherwise, you may just have to drive it and stop fixing stuff that isn't broken.
You may have to wait until a code appears.

Italianjoe1

iTrader: (6)

Pull the spark plugs and look at them, the one that's misifiring will be darker/wet with fuel or lean/burned from lack of fuel. That will give you more direction.

myfirstzcar

I'm pretty sure he mentioned having a random misfire, which could be any cylinder at any time.

paul7002

Ive checked the plugs on bank two they look normal. The tbrottle bodies cannot be swapped I wish they could. Im pretty sure this is a fuel mix problem so most likely air. Since the problem occured after I did the air filters and cleaned the throttle bodies I just keep guessing the throttle body on that side is screwed up. Also now I remember having an idle issue trying to reset and relearn. Maybe I screwed it up somehow. I know there are dischssions on throttle bodies and OEM but I know I can get a new one like the OEM at Advance Auto for about 150 with a coupon not too bad. Ill try that soon dont really know of anything else to try.

myfirstzcar

Did you say you cleaned the mafs?.....With actual maf cleaner?

Italianjoe1

iTrader: (6)

That just means the car can't determine which cylinder via the PCM and crank angle sensor, not that it isn't just happening on one cyl.

Seeing that his sample is so small, he has to force the car to misfire enough to even set that code, the chances of it triggering a 301-306 cyl specific code are pretty slim.

Italianjoe1

iTrader: (6)

Problem with a throttle body is that it won't just affect one side, the manifold is open inside and at low RPMS there's no way that it couldn't balance out enough to feed both sides even if one of them was closed completely.

I'm still thinking a fuel injector but since you say the plugs are fine there's not a lot to go on there.

I have a full set of HR injectors and rails, i'd say swap them in if you were close but it's still a lot of work to hunt down this issue.



One more suggestion: With someone helping you, have them hold the car at the misfire point and pull the coil pack connectors off one at a time, see if one gives a smaller/no change than the others. At this point you have an air/fuel mixture problem on one cyl from the sound of it and you need to isolate it before you just throw more parts at it.

zakmartin

Jesus Christ, you really don't know what the hell you're talking about, do you?

myfirstzcar

Don't be a douchebag.

I don't own an HR, and have never worked on one....HOW THE F#CK WOULD I KNOW THEY'RE NOT THE SAME?

tangi

Hello !
does the problem has been sold , i have ( i think ) the same problem!

Thank's
Tangi