Why R33-34 Gts-t (and Not 32 Or Gt-r) Misfire/stutter Exactly @4000-4500rpm(long Lol)

[silversr33]

Follow up: shortly after writing about this I went down to the garage, disconnected the battery, pumped brakes etc, earthed boost solenoid black wire, reconnected battery, reset ECU and took the car out for an hour long drive. It was noticeably stronger on boost, built up to and sustained up to around 0.85psi. First time in almost a year (yeah I been lazy ) I've been able to accelerate without stuttering/"misfiring". Didn't do it even once in the hour or spike any kind of boost or have the slightest negative reaction or suspicious knock or sound! Feels great I had forgotten how good this car could feel when it felt like this and it sounds huge again compared to when it was having issues lol. All without even glancing at a coil pack

**Disclaimer: I do not claim to know much at all about fuel management, fuel injection systems, forced induction, air/fuel mixture ratios etc. This is a logical explanation that I've pieced together by reading a LOT of stuff both on SAU, on the net, learning about how ignition systems work, picking up info about how the R33-34 systems work from unrelated threads... etc etc. I really didn't want to end up one of those poor guys who spent $600 on splitfires and then had another misfire heh. Parts of this are probably incorrect, feel free to point them out, but I'm hoping this sheds some light on the situation because this has been a f*cking pain in the ass for a lot of us for ages

It's also really long so if that's going to be one of your opening flames tough luck, I warned you

It was only when I started looking for info on better than stock coil packs that I was shocked at how many people experience this *same* misfire...and then I started noticing it only seems to happen at a specific rev range on r33 GTS-Ts and 34 GT-Ts, um and probably on stageas too actually, misfiring on boost can and does happen to GT-Rs and R32 GTS-ts on here regularly, and for (usually) related reasons, but NOT at that specific rev range.

In my opinion GT-Rs and R32s with tuned ECUs/or stock boost stock ECU experiencing misfires, etc are experiencing issues that appear similar but are in fact not like this problem at all.

I'm pretty much positive that no-one who is running an aftermarket/tuned/SAFC-controlled etc is experiencing this specific misfire and flat, stuttering spot at a specific rev range everytime (and almost always nowhere else). If you are experiencing misfires/boost stuttering/sharp boost cut.

And so....specific rev range...specific models...that isn't a misfire, it's done on purpose by the stock ECU as a harm prevention measure. I suspect you've noticed some pretty intense fuel consumption too heh, I know I have.

I think there has been an awful amount of frustration, confusion and $$$$ expended because we've been mixing up similar symptoms for a number of particular common misfiring problems.

You go to any mechanic, have a misfire under load, he'll go spark plugs, then he'll go coil packs, and if he's thinking laterally he might check out the injectors if the plugs have plenty of build-up, may even end up at the AFM and eventually do a A/F ratio test but rarely suspect that evil, paranoid little box is chucking a regular sad because it thinks we're having a little too much fun.

Why it does this though is that R33 gts-ts, r34gt-ts, stageas, have a stock 2 stage boost solenoid (unlike GT-Rs who have two turbos anyway and 32s which...I dunno just didn't get that yet). Lower boost at lower revs to give it a little pick up, then at that magic 4000rpm spot the VCTS (variable cam timing system, introduced with RB25det onwards) kicks in and the higher level of boost takes it from there.

It boils down to the ECU thinking we're going to blow the turbo because the ECU interprets the current level of airflow combined with engine speed, revs etc as a potentially harmful level of increasing boost compared to where the stock settings expect it to be at in this rev range and the ECU takes preventative action.

We could most likely get right down and figure out the levels if we really wanted to but practically I guess it works out something like this. The ECU doesn't actually detect boost, it's a vaccuum line that runs the stock boost gauge. All it does is take airflow readings, compare them to what its settings say is normal for induction, boost, exhaust, whatever, and as long as they're not out by too much there won't be a problem.

Overboost even a little bit and there will likely be a problem because of the first part of the two stage boost setup.

You guys who claim you are absolutely rock solid factory stock standard boost and this only happened after you installed a standard mod like exhaust, intercooler, maybe even pod filter etc - these all increase airflow and with enough flow our suspicious little friend thinks we're on the boost. I suspect the number of non-boosted cars that are experiencing this "misfire" are probably very low, but I suspect (and have no proof hehe) they would mostly be R34s (free-flow perhaps, aggressive ECU boost limits) and perhaps some stageas/r33S2 for similar ECU limits.

It's also quite possible if you've had the car only a short period that in fact it is boosting higher than it should be in the first boost stage and you don't know it. It takes about 2 minutes flat to insert the most manual of boost enhancers - a larger than factory diameter metal ring - into the vaccuum hose, and if you weren't acutely aware of your boost curve (eg not what it peaks at but how fast it's increasing) in the first 10 seconds of acceleration from low speed, and the peak was set at 7psi or less, you'd think you were running stock boost but the ECU knows better.

And we all know what happens next: *pop*, farting sounds, you probably ease off boost to wait it out for those few hundred revs while silently raging against the fact that you paid $600 for a set of ignition coils you won't need til you have about another 70kw at the wheels and then, it's all good til you stop again.

Our misfire is actually a damage prevention method often referred to as "Rich and Retarded" because at a critical point in the stock boost power band the ECU uses a harm prevention tactic which enriches the fuel ratio compared to the induction, while agressively retarding the ignition timing in order to circumvent the turbo. Why?

ECU just does what it's been told to and calculations show that at the current boost level, which has been rising in a linear curve instead of tailing off as expected before the high end boost kicks in at about 4500-5000, major damage will result if boost increases at this rate and as far as the ECU is concerned this is a major snafu in the car and if it doesn't do something it's f*cked.

R&R effectively prevents the turbo from making much boost at all, until it detects as it leaves the transition rev area between the low and higher boost stages that the boost is within acceptable levels (because it's spooling up again from scratch heheh) and then assuming you aren't peak boosting over about 11psi (r33 series 1: ceramic compressor wheel) and not over 10 for R34, R33 S2 or Stagea (more aggressive ECU, lower fuel cut cos of nylon compressor wheel), your boost will be back to normal and your "misfires" won't occur until you have to slow down and move through that same low gear rev range.

Course those of you who do exceed the 11/10psi limits (or thereabouts anyway) are probly familiar with the consequences - an extremely nasty complete fuel cut, which makes the entire car jerk (and from memory engine brake) to prevent critical stock turbo kaboomage as it very rapidly approaches its safe operating limits. You can imagine what that kind of shock does to the engine too - not good, but better than what it's there to prevent heh. Not that I'm defending my mean, paranoid little ECU.

So the "misfire", as evidenced by the fact that it always happens in the same rev range, to the same kind of car, and never happens anywhere else (otherwise you've also got a misfiring cylinder lol) shows it's actually not a misfire at all but intentional ignition timing retardation combined with fuel flooding to sabotage the rogue turbo.

If you've read many of these threads you'll see another recurring theme is that many will say that they are mildly boosted over factory settings, but if they take the boost back to normal it stops misfiring immediately.

Well that's one option yeah but let's face it, no-one wants to do that one.

Tricking the solenoid as per this thread might work ----> http

/www.skylinesaustralia.com/forums/HO...st-t42895.html

Haven't tried it, I think it would work but you might still want to ground that stage 1 wire if you choose to bypass the solenoid completely and use a larger bore in the hose - eg if you wanted to run 10psi in a S1.

Option two is obviously ditching the stock ECU, and have it remapped to your current setup. potentially expensive - it depends what your plans are with the car.

if you can't afford that, for a few hundred less you can leave everything as it is, get a safc/emanage etc and intercept the airflow readings and lie to your ECU

Those are pretty the options afaik, stick to factory spec, ditch the ECU or lie to it. And possibly just trick it using the solenoid.

Don't forget to check your sparkplugs, ignition coils etc too, if this has been occurring for a while there could be a lot of build-up...and gap the spark plugs correctly when you change the boost.

Also I reset my ECU after changing anything like that, but I'm not sure if it's necessary or if I just want that spiteful little box to GTFO of my life for at least a few seconds.

If your vehicle does not employ a two-stage boost pattern, eg R32 or GT-R then I can't see how you could be having this particular issue (unless someone slipped you a different ECU? lol) but you may be experiencing similar disciplinary action from Mr. ECU if you're attempting to overboost too much (but I expect the complete fuel cut at peak, rather than stuttering at low speed and hard boost acceleration).

You may also have an actual misfiring cylinder - in which case check your coils one by one, spark plugs, O2, etc.

**As stated at the start I'm not claiming this is all fact, it is simply an explanation for a very specific occurrence over a specific and limited number of models, and which only occurs in absolutely specific circumstances, operates in exact replication of a commonly employed ECU tactic especially amongst dual-stage turbocharged overboosted vehicles, and is therefore not a malfunction, and is based on official information, observations, considered opinion, outlandish conjecture, public domain knowledge of fuel injection etc and plenty of caffiene.**

Edited December 3, 2007 by silversr33

[Granthem]

wow long post... cant read that at work

[Taleb Tyres]

nice work, makes sense, but would this still hold if you also had a piggyback running (ie hks fcon s)?

[silversr33]

nice work, makes sense, but would this still hold if you also had a piggyback running (ie hks fcon s)?

Maybe not, if you had it set up properly...for me this came about after changing the spark plugs so I guess I knew it wasn't definitely the obvious ignition components.

My car is much better with misfires now though it still happens...it's fixed 90% of the problem but not all of it.