joshuaho96

The reversion issue is very real if you decide to go without any BOV. Or if the OEM bypass valves decide to stick closed from age. I have heard this badly impacts the resulting tailpipe emissions. The hot film MAFs are supposed to fix this by only measuring airflow in one direction.

In my experience it affects idle, it definitely uses the VSS signal to raise the idle target and adjust the open loop AAC duty cycle or something like that. If you push the clutch in while moving it will idle closer to 1200 rpm before very slowly dropping down to 950 rpm. More often than not you need to get it into neutral and make sure the neutral switch actually triggers by wiggling the shifter in neutral before it'll finally decide to drop the idle down.

Isn't that a slightly modified rebranded G42-1450? The GTIII-SS as far as I can tell really is an MHI TD04HL somehow adapted to fit a compact 5 bolt RB26 application.

If the rear diff cover is finned and your gauge cluster has an A-LSD warning light you have the A-LSD.

IIRC a lot of these Japanese chip tunes tend to have epoxy all over the ROM chip because they didn't want to make it too easy for their maps to get dumped. If the board isn't ruined by all that then Nistune is a pretty easy way to get a map figured out if only to reset timing/fueling for local fuel quality.

Good to hear. Any air bubbles in the system will drastically affect A-LSD and ATTESA response time. I personally have never noticed the ATTESA reservoir doing what you said either.

The only reason I can imagine going for cast is if you want very tight p2w clearance. I'd have to check again to be sure but I'm pretty confident a 4032 forged piston like Mahle or Tomei is on par with OEM cast for p2w clearance spec.

https://page.auctions.yahoo.co.jp/jp/auction/g1127754625 Appears to be discontinued so... that's a bummer

Do some ECU logging. Consult cable + Nissan Data Scan 1. Try to record a 14 psi pull then a 7-10 psi pull. Make sure you record airflow + airflow RH, throttle, RPM, injector, ignition timing, and wastegate solenoid. If the solenoid indicates it's on in both cases and you aren't on knock maps then my first suspicion is the wiring to the solenoid might be intermittent. Next step from there is to unplug the ECU, get some long wires and verify the wiring from the ECU to the solenoid maintains solid contact/low resistance, jiggle the wires while probing to see if it drops out at all. If all of that checks out you should try capping the plenum to wastegate hose, then test with 3/5/7/10 psi regulated pressure and figure out the minimum pressure needed to barely move the wastegate actuator, then how much is needed to really get it to swing open. The R32 engine manual has a more specific spec for these things but if it's like 8-9 psi to really get it to swing open then it's fine. You can try putting as much as 20 psi into the wastegate actuators to see if it opens smoothly and doesn't make weird noises/rattles. If none of those things are conclusive try removing the intake piping enough to look at both turbo inlets. Or the turbo outlets in the exhaust if you prefer removing the down pipe and turbo outlets. Make sure nothing is damaged, no shaft play, etc. If none of that figures it out then I dunno. Post back and I can noodle on this more.

TPS input voltage being higher than the ATTESA expects will cause weirdness for sure. Also goes to show diagnosing these faults is never a dull moment it seems.

It's worth it because you can flip it for 1400 USD on Americans that can't look up part numbers for some reason.

Didn't Nismo just announce they're making these? https://www.nismo.co.jp/news_list/2024/news_flash/24005.html

Right, I'd need to be able to log exactly where the stock ECU is in the fuel tables to see where it's actually going into high load enrichment but it doesn't take much of a grade in my experience to start getting into positive pressure. God forbid you're closer to 80 kph, the reserve torque margin gets very thin around 2000 RPM, 2800 IIRC is min BSFC according to Nissan's dyno data. The R34 GTR 3.545 is to some extent compensating for the shorter 6th gear, roughly equivalent to a 3.7 with the FS5R30A.

My math did put it right around 3.7 final drive being about ideal for highway cruise but it doesn't really consider anything else. I thought about doing similar on an R33 GTR but I find myself using pretty much all of the reserve torque in fifth quite often. The spacing between 3rd and 4th is also kind of strangely small while the gap between 2nd and 3rd is huge. The other thought I had was final drive ratio changes requiring speed sensor recalibration so I mostly gave up on those thoughts. PAR engineering also offers a 0.7 5th gear. I still don't really know if their ratios are the way to go or the more common stuff like PPG/OS Giken/etc.

It runs fine but it'll cause a bit of weirdness, the ECU definitely uses the speed sensor input for idle. Sounds like OP needs a tune anyways so just do a power run in a lower gear to avoid hitting the ECU speed limit for a baseline and then run a standalone to sidestep the issue. RB26s seem to really hate going much below 1000-1200 rpm especially if you put any kind of load on them so it's nice to keep around for refinement reasons. Or maybe I just need a new harmonic balancer.

Whatever your ECU is will have a program that lets you pull ECU logs.

Make sure your O2 sensors agree with each other, make sure your MAF is generating sane values. Make sure your injectors aren't clogged or seized. Make sure your fuel pressure is good and isn't dropping out at higher load. Make sure you don't have any vacuum leaks.

Check grounds, see what happens if you unplug the ATTESA fuses.

Factory R34 GTT should be at ~3100 rpm indicated at 75 mph (120 kph). Easy way to tell if there's actually any room to run a taller (lower number) final drive is look at manifold pressure at highway cruise steady state. If it's already pretty close to atmospheric leave well enough alone. On an RB26 the ITBs obscure some of this but there's really not a lot of room to drop engine RPM.

Curious to know what others think of this, in my head this doesn't quite make sense. I'm thinking the explanation is more like the RB25 can keep the turbo spooled for a wider powerband so more power on average -> more heat to dissipate. Everything else kind of seems like a 2nd or 3rd order effect that wouldn't make a 30+C delta in oil temps.

Yeah the problem there is for some reason Nissan doesn't sell most of the vents separately, it's only sold together with the whole center stack surround piece for reasons beyond me.

I'm also searching for some way to fix my R33 center stack vents. Somebody broke some of the louvers where they connect to the vertical adjustment bar. I bought a used one but I can't just throw it in because half the tabs are broken. I honestly have no idea how I could non-destructively remove the old louvers from my car and put in the "new" ones.

http://www.mines-wave.com/english/CATALOG/ECU/VX-ROM_NISSAN.htm#SKYLINE Stagea 260RS says it can be done on a trade-in basis. I guess you're right in that there is no separate ROM chip and doing the rework will suck but sourcing the right Hitachi H8, programming the onboard flash storage, and soldering on a new one with the speed limit set to whatever you want it to be is entirely possible. The only question in my mind is whether you can even still buy programmable H8s in the right formfactor/automotive grade/etc. A lot of the tuners in Japan absolutely still have all the hardware necessary to do the programming otherwise you wouldn't see companies like Nismo still hawking remapped stock ECUs with their engines. Techtom was the same thing. Only reason to bother with this is if you have no plans to change anything. Stock tune, stock car, etc. Otherwise I agree, skip all this nonsense and go straight to Elite 2500/G4X/KV8/etc. But from personal experience truly achieving 100% stock equivalency on a standalone ECU is very, very difficult and I don't think any tuner out there actually cares either.

Factory wheel is a 17x7J supposedly so 225/50R17 is probably the actual tire size.

There’s a bunch of Japanese ROM solutions around. It may be built into the MCU but the advantage of japan still living in the stone ages for this stuff is you absolutely can ask them to give you a ROM chip that is stock but with the limiter removed.