Bought car for 9k in 2013 @60k mi
Car had minor defect to paint, and interior was like new
Car had small hole in exhaust near muffler that made the car more responsive, deeper growl, and more fuel efficient....until the hole widened, then the performance went away, and my story of modification started...

Mods:
Stillen Cold Air Intake, Z-Tube, K&N Cone Filter
370z Injectors
ACT Stage 1 Racing Clutch
ACT Lightweight Billet Aluminum Flywheel
Stillen Headers
Stillen High Flow Cats
Stillen True Dual Exhaust Gen 1
Walbro 255LPH Fuel Pump

Hi everyone, I have been chasing the original responsiveness the G had when I first bought it to no avail.

I have added many modifications(the ones you see above), and replaced almost every sensor/electronic/component under the hood:
Knock Sensor
Knock Sensor Harness
Cam sensors
Crank Position sensor
Maf Sensor
Rear 02 Sensors
Front 02 Sensors (1 twice on drivers side)
Spark Plugs -OEM
Coil Packs -OEM
Coil Pack Sub Harness(connects to coils 1 and 3)
Injectors -2008 370Z
Battery(cleaned Ground)
Clutch Slave Cylinder
Differential Oil
Transmission Oil
Front/Rear Wheel Speed Sensors
Throttle Position Sensor
VTC Solenoid Valves
Evap Canister Purge Solenoid Valve
Fuel Pressure Regulator Passenger Side
Fuel Pump/Filter
Oil Pressure Sensor

Sadly, after replacing all of these parts, the only thing I have left I can replace would be the Accelerator Pedal Position Sensor, and the ECU that I know of...

I should mention that the car has been flashed with Osiris and dynoed at 280rwhp, however, the car does not feel like it has anywhere near that amount of HP at the wheels. The car is very sluggish on takeoff(feels like it is going to stall), and has no power up until 4800 RPM

I laid out every part that I've replaced on this vehicle the other day and thought to myself how does each part impact the issue I'm experiencing here. The ones that stood out the most were as follows:

-O2 sensors(upstream)
-Coolant temp sensor
-Maf sensor
-VTC solenoids
-Fuel injectors/regulators(dampers)/pump.

The only part I haven't replaced yet on this list is the fuel pressure regulator(damper) on the driver side connected to the fuel rail. I've heard it's very rare for this to fail. Also, the last remaining sensor on the car to replace is the Accelerator Pedal Position Sensor.

Guys, thanks for guiding me with this issue btw. If you ever need any help with your computers, audio equipment, modeling, or acting, please feel free to reach out...as those are my real bread and butter skills...

Back to the issue... Fuel pump replaced yesterday, sounds a little louder than the old, and shows no difference in performance(tired of writing that statement).
*However, I just found out something very interesting regarding the fuel level/responsiveness*:

-When the gas tank is under half full, the car struggles much more in the low end, wants to stall out, gas pedal is not hard to press.
-When the gas tank is full, car is more responsive in the low end, doesn't want to stall as much, gas pedal stiffens slightly.

Picture this, just so we are all on the same page.... I start the car, car idles fine, I start driving the car in 1st gear(wants to stall), shift to 2nd gear, while driving I refrain from pushing the gas pedal hard @ low rpm due to the fact that the exhaust gets really loud, and the car wont move/respond at all(bogged), once in 3rd gear, I steady the RPMS at around 4K(to have some power and not too much loudness), If I TAP the gas pedal lightly/consistently, and let the gas pedal come all the way back up from 4k to 4100, 4200, 4300, 4400, 4500, 4600, 4700, AND THEN OUT OF NOWHERE 4800RPM causes the car TO COME TO LIFE, and I can keep TAPPING THE GAS PEDAL up to redline with extreme responsiveness, and a perfect sounding exhaust.

I will be posting a few cipher logs soon to show this "tapping of the gas pedal" bizarre event I'm experiencing. oh and a video...

So right now I'm leaning towards Fuel Pressure Regulator(driver's side, attached to fuel rail), and Accelerator Pedal Position Sensor.

What do you think? Sell the car already, or keep stabbing at it?

 

-2nd gear pull while tapping gas pedal from 4krpm allowing the gas pedal to fully release in 100 rpm increments

-3rd gear pull while tapping gas pedal from 4krpm allowing the gas pedal to fully release in 100 rpm increments

-4th gear pull while tapping gas pedal from 4krpm allowing the gas pedal to fully release in 100 rpm increments

Cipher logs to follow.... please let me know what parameters other than RPM you would like to see....

Thanks,

Dave

 

I'd like to see MAF, MAP, RPM, knock, throttle, and spark timing. (Not familiar with that software and what's available to see)

I would put it back to stock and get rid of the injectors and go from there. There's too many variables at this point.

 

I will make sure I capture those parameters on my data logs this weekend.

Also, I forgot to mention this in the original post, but once I finished the fuel pump install the car performed perfect(stiff gas pedal, sensitive throttle input, fast response from rear wheels, tach jumped from 600rpm to 6k rpm with a light tap of the throttle in first gear, engine sounded great) for a few minutes when I took it for a quick test drive up the road.

The next morning the bogging returned, and I am hearing an intermittent electronic adjustment noise coming from under the hood(in the middle near injectors/second dampener) when decelerating from the 4k rpm mark.

Also, it should be worth noting that I experienced a flashing CEL P0303 a few months back when I revved the car through the gears up to 4th gear(from what I understand a flashing CEL gets produced when the engine runs for 6 seconds or more out of spec, which may hurt the cats). I have since replaced the cylinder 3 spark plug, coil pack, coil pack sub harness, and injector to no avail. When I put a screwdriver to the injector and listen on the handle, the injector sounds like its clicking slower than the other injectors. Could the wiring harness that connect the injectors be going bad? Has that ever happened with these cars?

My over the winter plan of action is to replace this injector(again), the fuel dampener connected to the fuel rail, the fuel injector wiring harness, and the top/bottom injector O rings. Unless anyone has any better idea of course...

This will be my last ditch effort to fix this vehicle, as I've replaced every electronic sensor/cleaned the grounds associated(ECU/ABS included), replaced every vacuum hose/gasket, and now have replaced almost all fuel related items (fuel pump, fuel filter, fuel dampener passenger side, evap canister purge solenoid valve)

 

P0303 is a misfire, CEL flashes when you get a misfire code usually. At that point you should get off of the pedal.

Also the pedal stiffness isn't changing with anything you're doing. The pedal isn't connected by a cable anymore, it's drive by wire aka there are sensors on your pedal that tell the ECU the pedal % and that correlates to a throttle % that the ECU commands the electronic throttle. So any effects of that are likely in your head.

My suggestion would be to take it to a specialist for diagnosis rather than throwing more parts and money at it. It could be your tune or any number of parts. If the wiring for the injector(s) were bad, it would probably be throwing a code.

 

P303 is a misfire and that's what's causing the CEL to flash.

The stiffness of the pedal is likely in your head. The pedal isn't connected to anything via cable anymore, it's drive by wire. If the injector wiring was bad, it would probably set a code and the injector wouldn't fire at all.

Have you talked to your tuner? My suggestion would be to send the car to a mechanic/tuner to look at rather than keep chasing this yourself. Stop throwing parts at it and get confirmation of what the problem is.

 

I agree with your first and third statement, and I worked with a tuner a few weeks ago who suggested to chase the fuel system, as all sensors have been replaced/not producing a CEL/vacuum leak test passed.

The stiffness of the pedal is in direct correlation with the engine timing. A softer pedal is indicative of too much retarding/advancement, which ultimately causes a lag in response from pedal depress to the wheels moving. Picture it like this: you push the gas pedal when its stiff, and the wheels will instantly react because the engine that is in between you and the wheels is taking your input and creating the output without resistance from the computer(advancement, retarding). OR you push the gas pedal when it's not stiff, the pedal travels about halfway to the floor before you receive any response from the wheels, while the engine sounds muffled, and your car almost stalls because the computer is not in sync with your input/the wheel output.

the tuner thought the fuel pump/filter was going to solve my problem...which it did for a few minutes(felt great btw, as the car went from feeling like a stock toyota corrola to feeling like a mildly modded g35)

Now there is a noise under the hood when decelerating from 4k that wasn't there prior to the fuel pump install...I'm all for not throwing parts anymore, cipher logs will be posted this weekend

thanks again for all suggestions, sorry if I'm coming off as a douche, but I'm kind of tired from throwing money/time at this vehicle, as the car should be pushing the hp/responsiveness we saw on the dyno, not what's on the pavement right now. I can post a video of me trying to keep up with a stock minivan of your choice from a stand still if you're interested in that...

 

It's your wording that's getting me. I see stiffness and think "difficulty to press the pedal." Like it's physically harder to push in one situation vs. the next when the pedal itself should feel exactly the same. As I said before it isn't hooked up to anything (spark timing, throttle, etc) that would change the actual feel of the pedal.

No worries, I'm just trying to help you sort it out. Not trying to sound like a dick either.

 

Oh, no worries bud, I'm speaking in reference to the physical resistance of the pedal when it's at the top of the range (not engaged yet). When you press the pedal there should be a resistance throughout the depression range to the floor, as opposed to my situation where the pedal shows little resistance until the halfway point, at this point the pedal starts giving resistance, and the wheels start to actually move ...

the car stalls on me all the time because of it...I'll push the gas pedal more than halfway to the floor and it still wont move the wheels until finally there's some resistance and boom the wheels start to move, and I'm thankful it didn't stall....It's quite embarrassing actually, because every stop light is like I'm hitting the reset switch to hell, as I know I will need to find this sweet spot with the gas pedal AND the clutch pedal as opposed to solely the clutch pedal ,if that makes any sense...

 

Definitely log accelerator pedal position and throttle % as well when you log. That definitely doesn't sound right.

 

Will do , and thanks for all of your support with this. Ill have the logs hopefully friday night or sometime saturday during the day. I plan to do an in park rev out to rev limit, 0-100 pull , 0-60 pull, 2nd gear till rev limit pull, 3rd gear until rev limit pull, and 4th gear till rev limit pull. Let me know if any other type would be beneficial here.

 

I don't think you'll need to go to 100mph. No need to get a ticket for this.

 

haha that's the one good thing out of everything I missed. slow car=no tickets...I knew there was sunshine waiting to peak through this dark cloud.

 

Maybe your tune is garbage?
Care to post your dyno up here?

Lots of time in modding these cars you end up giving up the bottom end power for top end power.
But typically bogging like this happens when your car has a vacuum leak. If you have had the manifolds off make sure that your gaskets are all sealing properly. This happened to me when I made my custom lower plenum, I ended up having to use some hylomar on the gasket in one spot so that it would seal.

 

It' odd, because I've considered the tune being the issue, but every time the car is on the dyno, it performs like a new Ferrari. Why is it that once the car comes of the dyno, it performs like trash? weight of the car, front wheels moving, not sure of any other variables here that could be affecting... And of course, when the tuner finished his dyno last time, it was raining, which disallowed us from doing a dry pavement run with his computer connected...might be worth taking another trip to Connecticut and driving with him at this point...

I will check my manifold when I go to replace my injector harness/fuel damper on fuel rail(what I think the problem is) , and replace all gaskets/ensure FSM is followed spec for all torque sequence/pressure in the meantime