1UZ Turbo + stock ecu: idle problem

[Fasteddie]

Guys,

the 1UZ LS400 with T88 is finally running!
Since we progress on the rwhp stage by stage we kept the stock ecu to begin with.
The T88 is currently only making 3-4 psi on "full" boost with AFR 10-10.5 so enough room to increase boost. We also use a Virtual exhaust system and external wastegate.

We now how the following "problem": when cruising (no boost) and SLOWLY braking the car nicely brings the rev down to idle position. But when driving (let say 30 mph,no boost) with ABRUPT braking the car can't keep the idle position and dies.
We already closed the wastegate and lenghtened the air intake (maf to close to turbo) because we thought of "compressor surge", this seems to help a little but still not solves the car dieing under hard braking.
This problem is even worse when coming from 6000 rpm and braking "hard"..


Any suggestions what to try ?...we do want to keep the stock ecu for now...

ps.what psi the stock ecu can handle (i read 7psi, but didn't find an explanation)..will the AFR go > 11.5 when boosting more then 7psi ???

THX !
:biggthumpup:

 

[Lextreme II]

Are you using MAF or MAP? If your BOV is too close to the MAF then this is very common. Make sure the BOV is at least 20" away from the MAF.

 

[Fasteddie]

We will have to change to MAP now....probably a MAP ECU (2)

What we did was (on stock ECU):
-with 1 small spring in the wastgate we got 2-3 psi...AFR 10 on full boost....
-with 1 large spring we got 6 psi...AFR 11.5 on full boost.....
-with both the small and large spring we got 8 psi...AFR 12.5...so too lean !

Strangely with both springs the wastegate shouldn't open before 14+ psi...so i wonder why we only got 8 psi on the boostmeter...

We placed to MAF in the intake after the intercooler and not before the air intake anymore....so the idle problem was gone, but the MAF now measures the "boosted" air...

Any ideas why only 8 psi with both springs ?...is the exhaust too restrictive ?

This was how we tested:
http://www.supras.nl/phpBB2/attachments/thumbs/t_dsc01997__medium__286.jpg

 

[Lextreme II]

Double check your BOV distant from the MAF.

 

[mkiisupra1982]

How is 12.5:1 AFR too lean?