Hot-Weather Engine Lag
 

I know there are several threads about heat-related performance issues, but I haven’t found anything that seems to explain what I've been experiencing in hot weather since I moved to Phoenix a couple years ago, so please bear with me. My Z is a 2010 with 80k miles, manual transmission, and no aftermarket mods or tuning. Whenever the outside temperature is above ~95 degrees F, the engine is very sluggish below 3,500-4,000 RPM, above which it suddenly surges to almost the normal performance level. In addition to the general lack of power in the low-to-mid RPMs, it sometimes feels very jerky - when I press the throttle (smoothly - I'm not mashing it), the car lunges forward for a split second before pulling back to reduced power. The engine is even slow to rev with the clutch disengaged, e.g. when starting from a stop or rev-matching for a down-shift. The RPMs also tend to take longer than normal to start dropping when I lift off the throttle, which makes it harder to up-shift smoothly.

There are no warning lights when any of this happens, the coolant temp is a couple dots below the middle of the range, and oil temp is between 200-220F. When it's cooler outside or the car has been parked for a few hours, it performs very well with NONE of these symptoms... there's a substantial difference in drivability between my morning and evening commutes. I also never noticed anything like this for the first three years I owned the car (in Philadelphia, which is obviously not as hot but does get into the high 90s and occasionally triple digits).

I have been to four different shops (one Nissan dealer, one independent shop, and two tuners) which checked/performed the following: cleaned the MAF sensors, replaced a faulty MAP sensor, did throttle body and fuel adaptation relearn procedures, checked a brake light switch/circuit (apparently there was a TSB related to this), checked the fuel pump pressure, and checked the O2 sensors to rule out plugged catalytic converters. I even test-drove a brand new Z with the same weather, oil temp, etc. and didn't experience any problems.

Does anyone have any other ideas of what could be causing this? I'd like to keep this car as long as possible, but I've been so frustrated with the way it drives in the heat that I'm just about ready to trade it in for something else if I can't come up with a diagnosis/fix.

There are several high temperature nannies - oil temp and IAT are two off the top of my head. The FSM (link in my sig) will have details. Get an OBD tool that will let you monitor IAT, etc.

Do you have oil cooler? For the engine oil?

Sounds like it is pulling timing because of the heat and when you get up to speed you have more airflow and cooling so it behaves better. I bet your intake temps are pretty high!

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Alright, I got a Kiwi 3 and Dash Command for my phone and started doing some data logging. Unfortunately for some reason the only data set that actually saved was from this morning, which is not very relevant since the ambient temp was only about 90 degrees and I wasn't experiencing any issues. But for reference, the IAT ranged from 115 when stopped to 104-108 when driving 45-50 mph. Is there a certain IAT threshold that is known to cause the ECU to start reducing power? I'll see what I get while driving around tomorrow afternoon.

No I don't but like I said, the oil temp usually reads 200-220 when I'm having these performance issues, and it rarely goes above there. From what I've read (and experienced via two test drives of new Zs in the same conditions), it seems like that should be fine...

Any tips on how to analyze/interpret timing changes? I have the data plotted but don't know what to make of it since I'm 100% new to this, haha.

IIRC, the ECM starts reducing power when IAT gets to 85-90F. FSM should have details.

Could be poor fuel quality,,,are you experiencing any oil consumption?
wouldn't hurt to install a fresh set of plugs & inspect plenum for oil residual.
I see 200-210* oil temps all the time & even 230-240,,,but i back off & let cool.
My coolant gauge (dot's) stay consistent, 1 left of center-never any higher.
be sure air filter's & boxes are clean.

I not sure what to tell ya since mine was tuned and modded six months after I bought it and Seb gave me a hot weather map that pulled a little more timing than normal and I never really experienced anything other than would be expected with high temps as the performance is going to be lacking when temps are above 100*. I really baby the car when it is that hot and if I have to do full throttle pulls they were short and brief. I hear you that your oil temps are not that bad but I would also encourage you to get at least a 25 row oil cooler. More protection is better and take some stress off your system. It kind of crazy on 100 plus days and you start the engine and your oil temp is at 140 or 160 just setting in the sun. The bottom line heat is not a friend to combustion engine.