Why is my boost so high?
 

There's a glutton of 'low boost issue' threads out there, i know because i read 'em all trying to fix my low boost issues!

Low boost issues were down to:

- No hose with Pill going to wastegate actuator (just normal hose)

- hoses going from Wastegate actuator and precontrol actuators were into the wrong solenoids (unlike the usual when the connectors are on the wrong way round, this time it was the pipes!!!)

- cracked hose going from pressure chamber to rats nest

- faulty one way check valve going to pressure chamber

- faulty one way check valve going from vacuum chamber to IM

- and a couple of other hoses loose

So, with the low boost sorted i was smiling all round, my secondary was kicking in and the car was SO much faster.

However, the boost was then *sometimes* ok (10-8-10) but then most of the time 14-12-14.

My ECU at this point was a mines ecu and after checkign with mines they said that the 'boost limit is raised' to 0.9 KGCM2 so i thought 'this makes a bit more sense, that's why my boost is high'

Fast forward to today and i've just setup my new Apexi and FC Commander :nod:

I reset it to base map and proceeded with the learn process, which was fine, i understand that this should revert to a stock 10-8-10 pattern, but tonight when i 'tested' the boost it was still hitting wayyyyy to high, 14 psi and giving me fuel cut.

Can anyone offer any thoughts that makes boost too high? The way i see it the Apexi should now control the boost limit above the spring pressure of the wastegate and pre control actuators?

unplug these solenoids and you get mechanical boost limit (7psi?)

plug these in and the ECU should control what's happening after 7psi.

Can anyone confirm my above thoughts?

I use my FD3S as a daily driver and ideally i'd like 10-8-10 stock setup, but i like the Apexi and commander for it's more in-depth diagnostics etc.

There is no system on the ECU that controls boost. The only thing that controls boost on the car is the pill in the boost line going to the actuator and the wastegate spring. If your getting high boost, its probably cause you freed up the exhaust flow. Port the wastegate and get a boost controller. Solved. The solenoids have to do with pre-spooling, not boost control.

thewird

I've not freed up the exhaust. It's a standard JDM exhaust with an HKS back box.

If the wastegate and pre-control solenoids only contol pre-spooling then why if you unplug them do you only get 7psi from pri and sec?

in addition to this, if my CAT was smoked, would this cause my high boost? Surely this would behave like a 'freed up' exhaust?

What do you mean if your cat was smoked? Often times a bad or clogged cat will restrict exhaust flow, but if you have hollowed it out and its wide open inside there then yes it would free up flow and possibly cause the over boosting.

You need to list ALL modifications you have done to your car.

If "somked=open" you are lucky you still have a engine :uh:

Ok. From the top.

Arc induction kit,
Standard JDM downpipe and CAT, HKS super Drager backbox.
Standard sequential twins.

I've not opened out the CAT or anything, i've not touched the intake or exhaust.

Before the Apexi the boost was hitting 14psi.

hope that helps.

I run no cat just 5 inch open down pipe on a samurai with a 93 13b single turbo microtech controlled and still got engine. I dont know whats your point.

^ and I'll bet you're also not running stock fueling....

Comparing a single setup (who needs a 5" DP????) to a stock one is just silly and is a horribly inaccurate comparison.

Ok, so steering this back on track...

Reasons for boost levels hitting 14psi?

wastegate not behaving properly? hoses with restrictor pills in them not letting enough air through?

Get a boost controller, your car isn't stock anymore.

thewird

Any time you open up the flow, boost will rise. You have opened up the flow with your ARC mod, and catback. Your stock down pipe also flows well. Remove the wastegate pill and drill it out ever so slightly. This will reduce your boost.

Can i put in a manual boost controller into the wastegate pipe to replace the pill?

i have a couple of dawes device ball and spring valves handy.

Electronic boost controller is always preferred, however on a setup like yours, I wouldn't hesitate to use a reliable mbc.

thewird

Yes. Put a MBC in the wastegate line. Don't do anything to the prespool line.

Thanks for the advice,

in the absence of an EBC at the moment, i'll stick in my dawes device.

I tried this setup https://www.rx7club.com/showthread.p...+boost+control

however with both MBC fully unwound (infact i took the ball and spring out both them to check) i was still hitting 14psi up!

:(

your setup sounds much like mine. downpipe, catback, intake. PFC

with stock pills, stock solenoids, stock piping, and proper boost values in the PFC, i get a solid 0.8 bar across the board. maybe something is leaking the boost in the precontrol/wastegate plumbing.

the hoses exiting the actuators, going up to the solenoids are vented by the solenoids. if you leave these vented (open) the actuator will not open. this causes overboost.

if you must use the MBCs, have you tried capping the other nipple on each actuator? some people reported having better results with MBC.

also, are the actuators still connected to the flapper door arms? someone reported a missing clevis pin being the source of his problems

Hi, yes the actuators are working, i've tested them,

when using the MBC i DIDNT cap off the venting side (i should maybe give this a shot)

If i plumb in my MBC to the WG pill line, what should i do in the PFC under turbo setup, should i disable the PFC from controlling turbo?

the way i see it, there will be no control of the WG duty cycle (if i block off the WG vent pipe) but i will retain Pre-control duty cycle?

Leave the powerfc alone.

thewird

i concur

I unplugged my WG and PC Solenoids to test the actuators, and i get a steady 7psi of boost.

if i had a problem with boost creep due do my intake/exhaust, wouldn't it have an effect on my 7psi test?

Yes, it would. You don't have a boost creep issue.

thewird

So what 'is' my exact issue. You've stated that my problem is down to the de-restriction in my intake and exhaust but don't elaborate to the exact nature of why this causes an increase in boost.

Lowering the Duty control on the wastegate solenoid through the PFC (so it's venting less) should surely have some kind of effect on boost level (even if it's minimal)

your statement - "There is no system on the ECU that controls boost. The only thing that controls boost on the car is the pill in the boost line going to the actuator and the wastegate spring." i find incorrect due to the effect on boost limits when unplugging the WG and PC solenoids. Your statement would be correct if both 'vents' on the actuators were capped off.

Perhaps i'm totally wrong, i'm only putting to the table what i've learned from troubleshooting my low boost issues, and living in my rats nest :)