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Originally Posted by silversr33
Hmm, thing is what's happening at 10psi+ on stock ECU isn't R&R, at 10psi the ECU is in serious danger mode that's Fuel Cut.
If you've ever tried to exceed 10psi on a stock ECU r33 SII, or about 12 absolute max on a SI you'll suddenly feel like you've hit a brick wall, boost will be cut instantly and it jerks the whole car very violently. First time it happens you'll probably wonder what the fk you just did to your car heh. Anyway that's when the ECU feels boost pressure getting dangerously close to stock turbo limits (at or going juuuust above 10psi for SII and r34gt-t, 12psi for R33 S1) the ECU goes boom and cuts the fuel supply which kills boost.
So yeah, that isn't R&R, that's fuel cut and it's much more immediate and severe than R&R - and needs to be cos the ECU uses it when you are at or just less than 2 psi from what is considered breaking point for the stock turbo (12psi for SII and R34, 14 for SI).
I'm sure you can imagine how fast an overboosting wide open throttle could build from 10psi to 12psi to 14 then boom...like maybe a second or two heh, if that.
R&R seems to be commonly confused with fuel cut, and I think if I had a dollar for everytime someone mistakenly messed with their AFM, spark plugs, coils and injectors to fix a "misfire" that was being induced on purpose by the ECU retarding the ignition timing because its factory settings cause it to misinterprete mild boost tweaking as rapidly approaching turbo destruction
R&R isn't as immediate or severe as FC but worse almost because it's very frequently misdiagnosed as a normal misfire where one of the spark plugs or ignition coils is missing its turn under high boost etc.
The situation can be caused by a faulty AFM, but you will never see R&R at the peak boost limit, only fuel cut, and likewise fuel cut couldn't be mistaken for a misfire in a million years.
R&R seems to be used in situations where the boost levels are not really even close to critical meltdown level, but the increasing boost curve is not following the boost settings the ECU expects it to, and should the curve be projected at a linear increasing rate - which to be on the safe side is what the ECU has to assume - that if something is not done it would cause potentially serious damage in a few seconds time. To control it the ECU floods fuel (Rich) and delays (Retards) ignition timing briefly, and this often results in a misfire, while the oversupply of fuel combined with momentary lack of combustion and access to exhaust causes the turbo to be unable to continue producing power at any efficient level.
It can concievably happen on stock boost on very cold days etc when air is much easier to compress, and S2 and later GTS series ECU's are particularly twitchy because their lightweight nylon compression wheel spools faster than the S1 ceramic but it's also not expected to survive above 12psi while the ceramic is rated at 14.
Far more commonly it happens because of even minor overboosting on R33/34s, (not GT-Rs or 32s) and always well below the danger thresholds where you'll experience fuel cut at 10-12psi.
R33 GTS-Ts, R34 GT-Ts and stageas (and prob ceffies not sure) really frequently have R&R "misfire" and stuttering issues at about the 4-4.5k rev mark down low in the gear ratios during on-boost acceleration, where the boost prior to that rev point exceeds 5psi.
It's cuz people use bleed valves and such to increase boost at a linear level across the rev range...which is fine for some cars, but the models listed above have a factory 2 stage boost setup as standard which runs a lower boost very early on in the acceleration to make it a little more friendly in traffic, more torquey and less laggy at low speed. Within only a few seconds of firm acceleration the ECU gets ready to tell the solenoid to switch to it's full (stock 7psi) boost for the rest of the rev range.
So if you've manually boosted to 9psi, when it gets to that 4000-4500rpm range the ECU is expecting a 5psi setting to give way to a higher 7psi setting but is recieving data indicating a linear boost spike well above factory settings, not close enough to the absolute boost threshold to warrant a fuel cut but the projected curve indicates it'll get there fast.
So it uses R&R to prevent it spiking to dangerous levels. For a while you'll probably notice the sputtering every time you accelerate and not know what it is, after it has been doing it every time you accelerate for a while it will usually cause a misfire when it retards the ignition. You'll struggle a bit through that rev range without boost building or sustaining, at about 5k it'll build again and will generally stay solid til redline or you hit the factory cutoff threshold (and serves you a fuel cut) depending how boosted you are.
So yeah anyway, detailed explanation but there seem to be an absolute ton of people spending money on trying to fix elusive misfires that actually have nothing to do with faulty ignition components.
It's also easy to avoid - if you want to boost a little at stock you need to take the stock boost solinoid out of the boost control loop cos then the first boost stage won't be initiated, which means the ECU won't go "wtf?!" at the rising boost when its expecing a second stage, so it won't try and flood with fuel or retard the ignition.
There are a number of ways to eliminate the boosting safety precautions being executed too, but ultimately this all obviously relies on your ability to know what a reasonable level of boost is before you apply too much strain to stock internals.
More efficiently, as above posted get a remapped ECU for your setup, piggyback ECU or fuel regulating attachment like SAFC or e-manage.
I've seen pages upon pages of people posting about their R33/34 sputtering and misfiring and being told (in good faith) to go buy $600 splitfires or get a new O2 sensor etc etc. to fix a "misfire problem".
Even experienced mechanics (like mine who has hand built custom drag car engines with power levels that make ours look like scooters) who aren't used to skyline-specific issues almost always assume this is a misfire caused by a faulty spark plug, coil pack, injector, etc etc until it becomes an expensive, frustrating drama that never actually fixes the boost issue, at most hides it, until you one day put an aftermarket ECU or piggyback on and suddenly find out what kind of performance you didn't realise you were missing out on. : /
Often the "misfire" is really elusive and after spending hundreds on plugs and coils it's still there...other times the coils do cover it up, while in the background there's problems every time you accelerate and R&R kicks in, flooding your ignition system with fuel creating buildup that fouls spark plugs and leads to misfires....heh.
Point being, if there's stuttering/R&R and misfiring, fixing the misfiring is missing the point.
The misfiring is not the problem, it's a symptom of it.
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