Strong gas smell when starting
 

Acts like it wants to die with both disconnected at idle, rpm’s fluctuate between 1500 and 600rpm, both maf’s are new


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That's odd, I haven't tested this on the Z but typically a car will default to safe mode that almost always runs smooth with no MAF reading (usually a good indicator if the MAF is bad if it's smooths out with it disconnected). I'll have to test it on mine.

Have you checked the basics like vacuum leak?

Triple checked and couldnt find any leaks even trying to hunt one down with soapy water. The only suspicious thing i happened to spot was what looked to be a tear in the outer part of of the intake manifold gasket.


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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.

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

http://www.the370z.com/members/z_eal...-ecu-reset.jpg

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.

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.

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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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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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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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).

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.

http://www.the370z.com/members/z_eal...06-mafless.jpg

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

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.

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.

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.

Interesting, so if i understand that thread correctly nissan mainly uses the af sensors to determine fuel trims. It does leave me wondering as i have only changed out my bank 1 af sensor if maybe the bank 2 sensor is throwing everything out of whack as that sensor is way overdue to be changed out?


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Is it normal for there to be cracks on the outer edges of the lower intake manifold gaskets that mate to the heads?


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Hey guys! have you taken alook at you spark plugs? Also when was the last time you changed them. if they are original plugs the gaps have widen out to the point that your not getting enough spark. but you should pull them anyhow and read whats going on in the chamber, you might might be surprised at what you learn. Just and old school thought.

Thanks for the suggestion boss, the spark plugs are less than 3 months old and looked fine when i inspected them while i had my fuel rail off, just a golden brown color. Original spark plugs i pulled out had the same golden brown color to them, but just worn out tips due to being in the car for over 100,000 miles


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All cars use the AF sensors for fuel trim. The mafs + rpm determine what cell on the map the car is in and the AF sensors give the feedback to verify the AF is matching the desired AF. What I was talking about was Nissan in the oem data does not list or use stft or ltft it uses that alpha data, something a bit foreign to me but I guess it’s like a combo of both.

Can’t say for Nissan but in my experience AF sensors don’t “age” and get lazy like a classic o2 sensor. If it’s way off you can use the rear o2 vs front AF readings to see if something is up.

Any best method for testing with the rear o2’s?


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I have not used this method to test post cat but I’ve heard it still works even post cat (maybe a slower switch), you can make a vacuum leak and watch all sensors react to it, rears should go low voltage like .1 ish and the fronts for the z I believe (I would need to double check) are a 0-5v with 5 being lean I think. If I remember reading right the nissans are opposite what a conventional o2 is and given in voltage. I found information on them before and they are a little different than some of the other AF sensors but now I cant find it.

Then you can force it rich with a little propane and watch all sensors switch.

Not sure if snap throttle method will work for post cat testing. Just an FYI some manufacturers actually use the post cat for fuel trim as well, some are more open about it than others like Toyota I believe the rear o2 heavily effects fuel trim.

I read in the fsm concerning the fuel system that the post cat o2 are not used for fuel trims when in closed loop mode, but then it goes on to say they are used in open loop and also to fine tune the fuel trims in closed loop mode....confusing to say the least


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Ok so snap throttle does work.

Slam throttle hard accel onto freeway (didn’t get that cap) and than snap off throttle. Also a cruise shot where they stay fairly middle of range. Should react fairly quick.

didn't get a recording of the wide range voltage which I believe my scanner is capable of picking up, but I did get a snapshot of what the post cat O2's are doing, to me at least if i'm interpreting it right it looks like my post cat O2's are reading a rich fuel mixture at cruising speeds compared to yours

http://www.the370z.com/members/z_eal...ost-cat-o2.jpg

Well mine were just a screenshot not a log. My scanner has great control for whole vehicle including bi directional control but sadly doesn't log, I have to use Ecutek for that. Yours look like they are switching so not really bad, they are able to go near 0 volts and up to about .800 fairly normal. It looks like it's switching maybe a little more frequently than what I think I should see but if that were truly the case you would have cat codes

So what do you think of the crack in my lower intake manifold gaskets, something to worry about or normal?


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When did all this start? After replacing the MAFs, cleaning throttle bodies etc or have you done all this because of this concern? It's not really looking like an injector issues as the two banks seem to be doing the same thing, it highly unlikely you have one injector on each side having a leak.

This all started around the same time i started having overheating issues after i had the dealer flush the cooling system, the odd thing with the cooling system is that the only time it overheats are when outside ambient temps are high and the ac system is going. Shut off the ac and the system goes back to normal temps. I’ve done a pressure test on the system to check for leaks and turned up nothing, switched out the thermostat which also did nothing, switched out the radiator which did nothing. Bled the system and flushed it multiple times to no avail, the only thing i havent done is switch out the water pump, but everyone I’ve talked to has a hard time believing the water pumps on our engine could fail due to their design. The only hypothesis i can come up with at this point is that the water pump is not moving enough coolant, therefore causing hot spots in the engine and throwing everything off. The car is very reactive for the first half hour to hour that it’s on, but the moment the emgine starts to get any amount of heat soak, the performance drops pretty dramatically to the point where i feel no power until after 5,000rpm. The only other symptom that i could point out that seems odd to me is that when the engine is completely heat soaked i start to get a light kind of tapping from what sounds like either cylinder 5 or cylinder 6, but goes away immediately after shutting off and restarting the engine


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Oh I remember that post. So the overheating has still not been fixed either? What reason did you change the mafs and clean throttle bodies etc? Did you ever do a block check on the cooling system? I can’t remember

Yup, performed a block check as well multiple times and turned up nothing. All i know at this point is that everything seems to be pointing towards heat being the instigator when it comes to the fuel trims and the engine bogging down. The only other odd thing i can point out that started more recently within the last two months is that from a cold start right as the coolant temps are getting up to normal if im accelerating i will hit a dead spot in the powerband that lasts for no more than a second and then the car will be completely fine after that until the engine gets heatsoaked and starts bogging down again.


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Hmm I’m kind of out of ideas for remote help. Any chance the AC compressor is going out and just poor timing after the cooling service (I highly doubt it)? I’ve never seen one put extra load on the system to make it overheat but I’m kind of lost here. Running lean would run hotter but your fuel trims don’t indicate that and you don’t have any fuel trim faults, all your ***** new and both banks seem to be balanced. Your in SoCal there should be some good shops down there but remotely (and not a Nissan specialist) I’m drawing a blank.

There is one thing i noticed after i had the ac system recharged by a shop i trust and go to all the time for things i cant do at my apartment complex. After they evacuated and then recharged my system when i replaced my radiator i get cold air, but not as cold as before they serviced the ac system. When the rpm on the car get up to about 2500 though it finally starts blowing very cold air like it did before the ac service. Not sure if that’s an indication of anything or that they just didnt service the ac system properly, but that’s the only other odd thing i can think of.


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Check your A/C for a leak. One of the o-rings at a connection may not be right.

Checked the ac lines for leaks this morning, no leaks anywhere


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Anybody know if it’s possible for drag from the ac compressor to cause overheating? I’ve seen mention of this on a few other car forums and just finished watching a video of a mechanic replacing an ac compressor on a 370Z and mentioning that the ac compressors on our cars go out quite often.


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So i did a little test and set the ac temp to outside ambient temp at night after the cabin of the car had cooled off.....ac clutch never disengages even after 10 minutes....is this normal for our Z’s?


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