1JZ boost cut

[mumblezzz]

I've had this problem with my engine since its been running. Under full load, boost pressure builds to about 0.9 bar and holds there for a while untill the revs gain where it creeps up to 1.0 bar where the ECU cuts.

The engine is from a JZA70 supra and it previously had a boost controller fitted but was just left with the lines from the wastegate hanging. I've looped the lines so they run standard boost pressure. Could it be the extra length of the lines thats causing it to spike?? Its becoming quite annoying.

[chrisellis]

no, i cant imagine it being the length of the lines, but if u want to make sure why not run the factory line configuration. Id guess its becasue of a decent exhaust on it. Mine creeps up close to 1 bar in higher rpm. But it doesent start at 0.9 bar, closer to 0.75 with dumps and exhaust. Why not just get an elec boost controller and set it to what boost you want and be done with it.

[chris davey]

EBC cannot lower the boost past the natural increase.

Wouldn’t think the extra length would make that much of a difference to spiking. I know that the shorter the lines the more responsive the boost controller will be. What exhaust mods do you have?

I would probably just get a jaycar DFA or SAFC and lean it out a bit (if you haven’t got anything doing fuel currently) which will increase the boost cut a bit.

[MR 1JZ]

pauly...my soarer did the same thing...it would hit just over 1 Bar on cold days...

and I didnt even have dumps

just get $80 together and find yourself a HKS FCD...I sold my old one for $80 just a few weeks back

[SL666]

now im wondering why mine doesn't go anywhere near that sort of boost..

[JZA70 R]

all depends of the quality of the breathing mods, condition of motor, turbos, wastegates ect ect.

a big exhaust w/o cat is enough to get to .9 bar in some instances.

i would be returning the wastegate lines back to factory configuration, not that hard to do, just make sure you replace the rubber lines with fresh ones. all it takes is a small crack or hole in one of those lines to have very unstable boost / boost creep ect ect.

if you do this and still have problems look at installing a FCD as others have said.

[SL666]

mine makes about 11 psi on a cold night.. but my cooler piping is less than perfect.. and i am running a cat.. big exhaust though..

[JZA70 R]

ditching my 3" cat netted me 2 psi, but with the stock cooler the ecu just saw the extra boost and threw more fuel in making the same hp.

[SL666]

mines mega-rich.... and makes 170rwkw at 10psi.. sub 10 A:F's

[JZA70 R]

they all are mate... all 1JZ ecu's are crazy rich... thats why there are some huge gains to be had from a tune.

i made 182 rwkw @ 11.5 w/ sub 10 AFR's

[SL666]

nice

im starting to think that i will fcuk the ECU off earlier than i really intended to..

[JZA70 R]

hmm yeah, well its a great ecu to get things started, but when your running out of mods to do then yeah, time to go aftermarket.

[mumblezzz]

Thanks for the help guys!

Exhaust is stock dumps into 3" with a straight through muffler at the back. No cat.

Breathing mods are just a pod filter, but 3" Intercooler piping all the way and a big front mount.

I think I'll be going the FCD. A friend has offered to give me one so that should work around it.

BTW: has anyone ever heard of a blitz boost jumper? I've go my hands on one but i've no idea how to wire it up. No one has ever heard of it. It looks like its just a less popular FCD than the HKS one.

[JZA70 R]

with those mods you will almost definately be hitting boost cut unintensionally (without boost controll).

FCD or stand alone management from here on.

[chris davey]

haven't heard of the blitz thingy. If it doesn't work, zener diode time

yeah, the no cat thing is why you have more boost than everyone else. I really should get rid of mine as well!