Strong gas smell when starting

Jhill

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.

Z_ealot

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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Jhill

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.

Z_ealot

One thing that i did try and this was purely by mistake is that i forgot to plug in the driver side maf when i reset the ecu, when i started up the car it ran really smooth but would not let me rev above about 1500rpm if that tell you anything


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Z_ealot

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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Jhill

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).

Z_ealot

as far as what I've read the FSM does mention consult III being able to perform an injector balance test, not sure on the residual fuel pressure though. one thing I did notice is that with the mafs unplugged the computer is not able to calculate an engine load as that value remained at 0 the whole time the mafs were unplugged. I'm attaching a chart to this post just in case ou were curious what the fuel trims were doing exactly while the mafs were unplugged.

Z_ealot

Tried to make it as clear as I could this time, but again, limited tools to work with lol

jchammond

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.

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Z_ealot

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


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Z_ealot

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Z_ealot

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

Jhill

Well it won’t have a load calculation because it gets that through the mafs. Without any load calc it will run like alpha n (rpm&tps) and use a map they know will run from internal testing. This will typically error rich and probably reduced timing (not an ideal running but something that is ensured to run). Again have not tested on Nissan to know if they just go to a total limp mode but others makes that I have disconnected mafs and driven for testing none come to mind that will go to a complete limp mode, in the past it was a good way to know if the maf was bad if it ran better without (although it could also mask a minor vacuum leak). So with yours disconnected your stft is pegged -25 and your AF’s are still indicating a rich condition. I’m not surprised it’s rich as I would suspect it to error rich but I’m a little confused by the stft. This may all be normal for Nissan, maybe with no load calc they just dump fuel and then the AF max rich causing the stft to peg -, I’ll have to see what mine dose.

Jhill

Ok so I went and tested my own and I think I have to apologize for leading you down a wrong path. Apparently Nissans absolutely will not run with the mafs disconnected, mine wouldn’t even start. I even disconnected while running to simulate a signal loss, it will barely run with one but dies with two and then no start, guess your stranded if you lose maf on a z. I am tuned on ecutek but I doubt they would eliminate a limp mode that oem had. Guess I’ve learned something myself through this.

Jhill

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.