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.