Originally Posted by Z_ealot (Post 3701000)

Unfortunately a scope is one tool i dont have in my arsenal, I’ll see if i can put together a graph of what exactly it’s doing at cruise speeds as i do have another data file that i recorded over an 80 mile trip after resetting the ecu that i havent processed yet. Appreciate the help in trying to track down this issue, it has been a pain in my side for the last few months trying different things to find out what’s causing it with what little knowledge i have and every mechanic I’ve tooken it to has said there’s nothing wrong with it that they can see


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Originally Posted by Jhill (Post 3701016)

Yea the graph isn’t helping me much, it’s hard without being there to get a feel and then have the graph re affirm my suspicions side from that it only shows what’s happening and not really a “why”. The part that stands out to me as odd is it not running well with the mafs disconnected. As I said I’ll have to test it on my own to reconfirm but I have never had a car not run “well” with mafs disconnected (like you’d be hard pressed to even know the maf was disconnected aside from the MIL). To me that feels as if there is something way beyond spec causing an issue. Typically as I said from what I’ve seen is the manufacturer has a pretty damn good idea of how the engine should run just from countless hours of bench testing and they build a pretty good map around that (like an alpha n tune) then the other sensors really fine tune it in but without mafs it runs off the data they’ve gathered that they can be fairly certain will allow the engine to run “well”. Hopefully that makes sense.

Originally Posted by jchammond (Post 3701018)

You Guy's are both plugging away at it!
Glad you got someone w/more knowledge helping you Z ealot! As none of my good contacts have got back w/me on this.
I read through most of what you guy's are doing; don't forget PCV valves & grommets.
And at this milage-probably wouldn't hurt to install new injectors (if you haven't already did this),,,Also when you remove plenum for gasket-inspect for oil residual/build up....may be time for catch cans.
You're gonna get it-I'm confident.

Originally Posted by Z_ealot (Post 3701039)

Thanks for the info jc :) i did replace the pcv valves about a month ago as i had noticed a lot of oil residue buildup on the intake manifold, fast forward to my visual inspection that i did on the injectors and i noticed the intake manifold is now clean after running the new pcv valves for a month, and yes i did go ahead and replace the injectors just to rule them out. The graphs i have attached to this thread are with the new injectors so i think it’s safe to say the physical injectors themselves werent the problem


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Originally Posted by Jhill (Post 3700979)

Well I'll have to disconnect my mafs to make sure the z doesn't do something different than what I'm used to but from what I'm hearing is it's running really well at cruise load but issues at idle (where engine are most sensitive). I've seen engines with moderate leak down (valve train issues) do this but it's usually accompanied by a rougher idle and an intermittent misfire but at 158k on an engine not known to have valvetrain issues I doubt it, vacuum leaks can cause this but I would suspect your fuel trim would be going + not -, mafs acting up (typically accompanied with a dead spot in the powerband) but I'll admit none of the car lines I've worked for had dual intakes but I assume it averages

both. I will say I have had one injector have a poor spray pattern sort of have the same symptoms you describe but again a rough idle and misfire that would smooth out and run fine at cruise with more airflow/turbulence to atomize the fuel (not sure what fuel trims would be doing as it was pre obd) but this is highly unlikely i think. Slightly leaking injector but usually accompanied with a stumbling start.



Do you have a scope with amp clamp? If so scope the amperage for the injectors power wire (before it splits into parallel) and see if all the injector amperage are relitively equal.

Originally Posted by Z_ealot (Post 3701184)

I tested the engine with no mafs connected again after i got home today, results are interesting to say the least. From cold start with both mafs disconnected the rpm’s fluctuated between 1500 and 2500 rpm until the engine coolant temps were up to spec at which point the rpm’s flattened out to about 1100rpm and only once about every 20 to 30 seconds the rpm’s would dip down to about 600 and then clim back up to 1100. Just a note, but i decided to check and see what fuel trims were doing after everything was warmed up. Long terms were pegged at 0 for both banks while short terms were pegged at -25% and would go to 0% when the rpms dipped to 600 and climb back to -25% when rpms came back to 1100. I tried driving the car while the mafs were disconnected, it would not let me go past 2500rpm, but seemed smooth otherwise. I recorded a few minutes of data while the mafs were disconnected that I’ll upload here shortly and see if we can glean anything from that if necessary.


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Originally Posted by Jhill (Post 3701200)

Probably won’t have time till the weekend to see how the z responds to no maf signal so I can’t say for sure. Would really like to see a residual fuel pressure check and injector balance test on yours (I can’t recall if the Nissan pcm has injector balance testing abilities or not).

Originally Posted by Z_ealot (Post 3701203)

also forgot to note that one other thing I noticed is that both banks AF sensors were recording a 0 voltage while the mafs were unplugged

Originally Posted by Jhill (Post 3701239)

Interesting read. Apparently Nissan does not work like other cars in terms of their fuel trims.

How to read CONSULT printout? - Nissan Forum

I can confirm because my scan tool gives the oem data and I was totally lost looking for stft and ltft and could not find it unless in generic mode. Great all my years on other lines won’t do me any good if I ever start to have an issue, have to learn my own car now lol.