2007 HR Hesitation - Nissan 350Z Forum, Nissan 370Z Tech Forums
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post #1 of 13 (permalink) Old 03-07-2017, 12:54 AM Thread Starter
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2007 HR Hesitation

This is my first post here so cut me some slack. (and yes, I have searched and done my homework before posting and no, I dont need you to google that for me)

Car: 2007 Enthusiast, 150K, adult owned and highway miles

Issue:
Regardless of if you are taking off slow or punching it, the car hesitates, feels like it dies, then takes off.

Notes: The car idles perfectly and once it gets going it pulls good. Fuel Trims are all within range. The Pass side AF runs around .4 to .6 but the driver side AF runs between .9 and 1.3 (strange?) but not much fluctuation, they typically sit at .4 (passenger) and .9 (driver) unless letting off the gas when slowing down.

History: I got the car a month ago. Ran great at first but then I started to notice the hesitation after a couple of weeks, then I got a P2A00 for the bank 1 AF sensor. Changed the AF sensor and then got the 420 (i think?) cat efficiency code on the same bank 1. I installed the new cats, no more codes but the hesitation is still there.

Steps taken:
Multiple computer resets by way of battery disconnect
Removed and cleaned throttle bodies
1000 different variations of the throttle body/idle resets I found online although Im not sure if any of them actually worked
Checked for vacuum leaks (nothing visible, no hissing and my vacuum is around 23 at idle)
New Denso Iridium Plugs
New AF sensor on passenger side
New Berk HF Cats
Cleaned Mass Air Flow Sensor (with mass air flow cleaner)
Seafoamed the gas tank and thru the brake booster (twice)
Inspected and tested the VTC solenoids, they are both clean and click open and closed with 12v applied although Im not sure if they are opening and closing all the way, dont have a reference point, just know that they are at least moving.

I havent changed the oil yet, it has 1000 miles on it and is clean but I dont know if it's the right weight. I have read that if not it can cause the VTC to not work correctly. I have also not checked fuel pressure, mainly because it idles so well and pulls so good once it gets going (although this is one of the next things I may check).

Soooo, anything that I am missing here? Does anyone know how to check the VTC covers or know how far the VTC solenoid shaft should move, mine probably moves 1/4 inch or so?

Thanks in advance to the 350Z guru that knows whats wrong with my car.
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post #2 of 13 (permalink) Old 03-07-2017, 03:02 PM Thread Starter
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OK, so I just did Throttle Body reset, again. Does anyone know if the reset works when there is no CEL to begin with? From what I see, the absence of the CEL post reset is what tells you it took. Guess the better question is since I dont have a CEL lit, how do I know if it worked?
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post #3 of 13 (permalink) Old 03-07-2017, 05:58 PM Thread Starter
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Ok, so one more possible clue. I can hear a distinct sucking sound coming from my intake plenum. It almost sounds like a blow off valve. If you hold your ear directly about the plenum you can hear it when someone revs the engine, it sounds like its coming from dead center of the plenum. It happens when you first punch the gas, you hear the sucking sound, the car hesitates and then it takes off. Apparently my car sucks!

So is this a normal sound, is it because the plenum is plastic and you can hear the air being pulled through or is it a blown intake gasket?
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post #4 of 13 (permalink) Old 03-08-2017, 01:46 PM Thread Starter
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Looks like it's the intake gasket :(
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post #5 of 13 (permalink) Old 03-10-2017, 04:26 PM Thread Starter
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Nissan has it at the moment, say they cant find anything wrong...This is crazy! If they cant find any issues, they will reflash the ECU.
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post #6 of 13 (permalink) Old 03-13-2017, 04:17 PM Thread Starter
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Nissan says I have a bad coil pack (cant tell me which one). Said that people typically replace them all instead of replacing just the bad one. $1195 plus tax!!! Funny thing is when I changed plugs I OHM'd out all my coil packs, they all read 2.4ohms. Also, I dont have any misfire codes and havent since I got the car. Does this sound suspect to anyone else? Has anyone else had a bad coil pack and if so did it cause the ECU to throw a misfire code? I had em reflash the ECU anyway even though they said that it wouldnt do anything, about to go pick it up now. Back to square one. Thoughts??
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post #7 of 13 (permalink) Old 03-14-2017, 02:34 PM
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OK- let me post here just b/c you've clearly tried to get some responses. First, I've never experienced your problem in either my DE-powered street Z or HR-powered race Z. What was the Nissan dealer's estimate of what a coil pack replacement for the faulty part going to be? FWIW- I think you're taking the right approach. If the coil pack doesn't address the problem, the tech will take the next step in the diagnostic tree to fix it.
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post #8 of 13 (permalink) Old 03-16-2017, 09:18 AM Thread Starter
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Thanks dkmura, Nissan wanted $1195 to replace the coils but they were purely guessing, they couldnt even tell me which coil was suspect. That just didnt make sense anyway because while I was changing the plugs a couple of weeks ago I OHM'd out all the coils and they were all good. I've lost what little faith I had in the dealership.

....but, I fixed the problem and the car is now in beast mode, no hesitiation, idles perfectly and will set you back in the seat!
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post #9 of 13 (permalink) Old 03-16-2017, 07:18 PM
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What did the problem turn out to be?
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post #10 of 13 (permalink) Old 03-17-2017, 08:22 AM Thread Starter
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Bad ground in the engine bay. When I checked from neg battery post to engine ground I found 1ohm, same with neg battery post to chassis. The grounds werent lose but after checking they were grounded to paint and the connections were starting to show slight corrosion, particularly where the ground connector met the chassis. I removed the grounds (battery to chassis, chassis to engine) and sanded off the paint and replaced them. After this I had 0.0 ohms from neg battery to chassis and 0.01 ohms from neg battery to engine. After this the car immediately went into throttle body relearn (i attempted about a thousand times before fixing the grounds and couldnt get into relearn mode). I did the relearn, let it idle about 10 mins and went and burned up the roads. ;)
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