Looking for some insight from other Z owners because I am new to owning one. This is going to be a lengthy post so I really appreciate anyone that takes the time to work with me on this.
I bought an 03 350z (6sp manual) about 5-6 months ago to use strictly for drifting, but I am having trouble diagnosing what exactly is causing the issues I'm having. To give some background, the PO of this car half-assed so many things that I have gone in and undone (some myself, and some with the help of a local mechanic that specializes in VQs). The engine has been pulled and we replaced cam & crank sensors, valve covers, upper oil pan, rear main seal, motor mounts, transmission mount, spark plugs, and upstream and downstream O2 sensors (all OEM except for the valve covers, for those we used the mitzone aluminum valve covers).

To give context: this car is completely gutted on the inside, welded diff, ABS lines are cut (I guess the PO didnt know you could simply cut the fuse for this and not the lines, but oh well), in-line hydro e-brake from GK Tech, pin 101 from the ECU has been pulled/cut (I believe this is for using the foot brake during a drift, not sure if 100% necessary), the exhaust is fully cat-less - test pipes, y-pipe, into a straight pipe with a 4" tip (this thing screams and is too loud for me lol)

I'm gonna lay out each problem and give my thoughts + any background.

Problem 1: The Z will occasionally go into 'limp mode' where I cannot go past about 2k RPMs and stuck at around 30mph, no matter what gear I'm in.
My thoughts/what's been done: The PO replaced the throttle body (non-em, I believe he used the Dorman 977-563 which Im not sure was a better choice over oem) and a new gas pedal and throttle position sensor. He never did the re-learn procedure for the idle/ecu, so I have already attempted disconnecting the neg terminal on the battery for 20+ mins, doing the re-learn according to the service manual which will resolve the issue temporarily but it keeps coming back to haunt me. I believe I have completed the re-learn procedure at least 3 separate times now. My suspicion is that the throttle body is no good or that maybe the MAF could be causing this? The piece that the MAF plugs into on the MAF assembly is broken on one side which I suspect could cause an issue (pic attached).

Problem 2: Specifically in 3rd gear, when accelerating past 3.5-4k rpms, the engine begins to bog and I start to lose power
My thoughts: I have no idea on what could be causing this. Third gear grinds on upshifts, but I'm good enough with rev-matching I can avoid the grind when downshifting from 4th. I do not get the acceleration issue in any other gear. I tested it out on a straightaway and I ran through each gear accelerating to 4-5k RPM before upshifting and I maintain top-end power and acceleration in every gear but 3rd. As soon as I hit 4k RPM it begins to lug and RPMs fall until I shift to 4th, 5th, 6th with no issues whatsoever. Idk if the gear being worn down due to the inherently bad synchros in these transmissions that it can cause this, but I cant seem to find any articles or other owners reporting this.

Problem 3: Engine Surging most noticeably at highway speeds, sometimes around 40-50mph & different exhaust notes
Noticed this one more recently, the engine seems to "surge" the cruising at highway speeds and sometimes driving around the city. By surging, it feels like the car wants to jump a little bit, almost like I'm quickly pressing the gas pedal and letting off. When this happens the oil pressure gauge jumps a little as well. The exhaust is usually a smooth drone while cruising in 5th or 6th gear but lately its not smooth at all. I wouldn't describe it as jumpy but more like very inconsistent.

Problem 4: LOUD chatter coming from bell-housing area, happens while idling and clutch pedal UP, don't seem to notice while driving at regular speeds
My thoughts: I am aware there are many owners out there reporting flywheel chatter on these cars, especially if you change to a lightweight single-mass flywheel, but I believe mine is OEM, I do not think the PO replaced this. He did however replace the clutch with a "ClutchMax" brand (not sure if it's their stage 1 or 2) but it's not oem. When I say loud, I mean LOUD! It sounds like a Diesel engine at idle. When driving at low speeds there is a loud clunking noise that seems to come from the same area that the chatter noise comes from too. I have already purchased a new clutch from Z1 with the 6 puck ceramic friction disk, and am saving up for the flywheel to match it. So I do plan to replace it in the future when I upgrade to the cd009 transmission.

Problem 5: Horrible fuel smell in cabin (exhaust set up: test pipes, y-pipe, straight pipe - all 4 cats removed)
My thoughts: Pretty sure this is just because the car is completely gutted with a fully cat-less and straight-piped exhaust. My guess is that the drain holes in the floorboard that are above the pipes are letting in the stink and this is only going to be resolved by putting cats back on the car.

Those are the main issues I'm having right now. If you have made to this part of the post, seriously thank you for continuing to read and I hope to get some feedback on what y'all think could be causing the issues I'm having.


Supporting Videos & Photos:

Problem 2: 3rd gear acceleration issue: - sorry for bad filming but I had my phone sitting next to me, you can hear me shift into 3rd gear when you hear the grind, and shortly after you can hear the engine lose power at the top-end around 4k rpm

Problem 3: flywheel chatter? - took a quick video when I got home tonight so y'all can hear the noise I'm referring to



broken portion of MAF housing

 

Hi @sock350z did you find the issue? Beacuse I have the same problem with my 350Z, I just already change the cam and crankshaft sensor also Knock sensor and solenoids of the variable timing control.

And I still losing power over 3.5 o 4k rpm.

Maybe I have to check out my Cats could be broken.

 

I’m not sure which specific issue you’re referring to, so I’ll cover a few of them

the chatter is most def coming from the flywheel which I haven’t dealt with yet

the power/accel issues were fixed when I replaced the MAF & MAF housing. The issue still comes back from time to time which i think is due to the fact I’m running an oreillys brand throttle body. Plan to replace with hitachi oem sometime in the future