1jz rev limiter / cut

[disc0-dan]

Hi guys

Just got my jzx81 back after getting the clutch replaced and a few exaust leaks fixed and its all been running sweet apart from one minor problem. It seems to break down at about 6-6.5k RPM and by that i mean it feels like the limiter is cutting in or its hitting boost cut. The rev limiter is set to the stock 7k thats posted on the digital dash and it used to rev to 7k no probs. The car was babied around for a few months while i was waiting on the clutch and exaust pieces to arrive and be installed / fixed. During this period the car driven almost 100% of the time off boost ( dno if that coulda caused something to foul up due to lack of revs ? ). Anyhow i havnt pulled the plugs or checked coil packs or anything like that yet, more or less just wondering if anyone else has any idea's as to what it could be ?

Also what is the standard 1jz boost cut level as ive only tested it on cool nights, may just be over boosting at high RPM ?

Cheers guys
Dan

[TJ]

Its probably hitting boost cut.

New clutch, exhaust leaks closed means it will making more boost and the car will hold it.

[disc0-dan]

That's what I'm thinking / hoping. It does seem to be making good power.

[thermus]

...seems to break down at about 6-6.5k RPM and by that i mean it feels like the limiter is cutting in or its hitting boost cut.

Is it cutting out all together (like you've got zero power) or does it feel more like it's miss-firing/breaking down?

[beatle]

Boost cut comes in at about 1 bar (might be 14PSI). have you got a gauge on it?

1J's are known to get spark break down when the coil pack 'stalks' deteriorate and crack. wrapping them in heatshrink/ electrical tape is the usual fix.

[Skitzo]

Dan, boost cut on the 1j is around 13/14 psi. I'll hit boost cut if the air temp is low. I'd almost guarentee that's what it is. Power cuts for a second, then get's back on it as if nothing has happened, until it hits it again.

[Risk10k]

FCD is an easy fix, not overly recommended unless you have gauge EBT etc, I think 2JZR31 can make them up for you - not sure if he's on here, but send him a message on performance forums.

[disc0-dan]

Running about 12/13 psi, its also very violent when it happens which also makes me think boost cut. SAFC will fix this won't it ?

[Skitzo]

Yep, boost cut will propel the body forward when on WOT.

As far as my understanding goes, it doesn't eliminate boost cut, but it increases it. Because you are telling the ECU that there is less air than there actually is, the car will essentially run more boost before it hits cut.

[disc0-dan]

Guess its time to save cash and get proper after market ECU

[Skitzo]

Start saving buddy. Think there is a PowerFC available atm for 1700 :(

Maybe also look into gettting a Jap Rommed ECU. Something i am highly considering.

[disc0-dan]

Advantages of Jap Rommed ECU ?

[Risk10k]

Boost cut removed, higher psi, more aggressive timing/fuel maps etc. Much cheaper than a full ecu upgrade..

[Skitzo]

They tend to have speed, rev and boost cut/limiters removed. Usually tuned for the usual mods ie, FMIC, intake, exhaust and sometimes bigger injectors. Higher boost and advanced timing.

[disc0-dan]

Sounds pretty good, im guessing Yahoo auctions japan is the way to go then ? How the hell do you shop there, its all in Japanese ? :-S Do you have an English link ?

[Risk10k]

PM Mayhem, he should be able to get you one ie; Brokerage service,

or you can translate the page..

[Endless]

Only problem with that is you have to cross fingers it's not too aggressively tuned as our fuel is shithouse compared to Jap..

SAFC would be cheapest fix but not ideal (used this myself for a bit when i went single)

Also one other cause if it isn't boost cut - coilpack connector plugs, when the insulation breaks apart inside causes a feel very much like boost cut.

[Skitzo]

Use importmonster.com.au/yahoo to search the auctions. Go through the categories on the side, then search using broad terms. Ie, JZX90, 1JZ etc etc. FInd what you want, then copy the actual yahoojp link into an email, and forward it to Jesse Streeter for a quote.

None on there atm though. Can also look for them on Soarercentral.com. If you find one, ask for the serial number, then contact the shop that did the rom and ask them what the ECU was tuned for. Should be able to tell you all the details.

Also, will ahve my hand on a FCD soonish. May offload it.

[beatle]

note that a JZX81 will run the same ECU as a JZA70, JZZ30's & JZX90's run a different plug configuration.
Jap tuned roms are also tuned for their atmospheric pressure, which is a lot different to ours. I run a Haltech interceptor on mine and would recomend it if you cant afford full standalone. can adjust fuel from 0-200% over standard plus has a decent range of timing adjustment.