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 :)

The duty cycle values are for spooling only. They have no effect after you are at full boost. The ECU does not control boost, the restricter pill does. Your car is no longer stock, therefore a boost controller is needed to keep stock boost levels or drill the pill as previously suggested.

thewird

I just went out to have a poke around, i was determined that my solenoids were to fault. I found that the hose from the pre-control actuator to the solenoid had popped off at the solenoid end. Now THIS can cause overboost, and in my case it was the cause. I took the car out to a nearby private road for some testing, on the way out there my boost was down at 8psi ( i lowered the duty cycles on the PFC to 30% and hadn't brought them back up)

when i got to the road i then upped the duty to 48% and this then brought my boost up to a nice 11-9-11 pattern.

So in conclusion while i do realise that a MBC is benefitial (in my case it wouldn't have made a difference as i was advised leave the pill in the PCT line and let the duty control that) i still believe it's possible to control boost with the PFC.

Weather here is awful just now, and it's not the safest testing environment but my preliminary tests are positive.

Im not trying to thread jack but my rx7 came with 3" downpipe and full exhaust and im installing a catalytic converter in the mid pipe and im wondering if this would create boost creep or will i need another one by the downpipe?

From my understanding - installation of a Cat will reduce boost creep - why are you putting in a Cat?

will you need another 'what' by the downpipe?

I'm still waiting for thewird to contribute to my last post.

another cat....sorry
I live in california and emissions are strict

Yup, good ol' Arnie.

You're going to put in a Cat, and a pre-cat?

I'm going to have to disagree with thewird about adjusting boost with the Power FC in this particular case, although he does know his stuff and I respect his input. The vehicle has few modifications and I would expect adjusting the boost control settings to help.

You can incrementally drop the "boost" and "duty" values to see if you can lower boost. Did you have the first or second option selected?

There is a low and a high boost setting built into the default map.

The low values (first option) are:

Pri .80 kg/cm^2 56% duty
Sc .70 kg/cm^2 64% duty

I would incrementally drop the target boost and the duty in alternating fashion.

So you would do something like

.80 / 50%
.70 /60%

.75 / 50%
.65 /60%

repeating a similar pattern. You're kind of fishing here. If you had a Datalogit you could log the boost and duty cycle and adjust it better from there. Whatever you do, in your situation do not raise it above the default values.

The "boost" and "duty" settings control the behavior of the solenoid valves. Think of "boost" as a sort of coarse correction, and a "duty" as more of a fine adjustment. "Pri" mostly affects the behavior of the precontrol solenoid, before the transition point that is set in the Power FC. "Sc" controls the behavior of the wastegate.

The best way to tune boost control with a Power FC is by using the Datalogit interface so that you can view charts. Here is an example... this is from a car that had some issues, but it shows what I mean. The vehicle had the stock 2 port bleeder solenoids but you can also substitute in 3 port solenoids like what you would find with a separate aftermarket controller:

https://www.rx7club.com/attachment.p...1&d=1341278206

On the right you can see the boost and duty settings that you would find in the Commander. Here I was raising them up in order to reduce boost drop off in this vehicle... later it turns out that the turbos were on their way out. To the right is the turbo transition control. It is mapped based on rpm and throttle position sensor voltage. On the right is the transition rpm point during acceleration. To the left of that is the transition point back to sequential mode during deceleration (hysteresis control). There is a trick where you set these values very close together to a low rpm and the PFC will control boost on a single turbo.

On the left side of the screen shows the log. Top is rpm. Middle is manifold pressure (Pressure Intake Manifold) load coordinates where 20000 is approximately 15psi with the way the MAP sensor is scaled. On the bottom is boost control solenoid duty cycle, where 255 = 100% duty and 0 = 0% duty.

hope that clears some things up.

If this kind of thing isn't for you, take thewird's advice and buy something like a Greddy Profec S. You just turn a couple knobs.

beat to it by arghx

Hi Arghx,

Thanks for the very detailed and interesting post - i was hoping you might turn up, i've read your other threads on the PFC control. :)

It is my intention to next get the Datalogit software.

at the moment i've put all 4 turbo settings to 0.75 and primary at 44% Duty and Secondary at 48%, this is giving me a 10-8-10 pattern.

Do you know what the function of having 2 'primary' and 'secondary' settings is? Is it for the learning that is mentioned in the FC manual?

I'm currently reading your other posts at the moment as i seem to be suffering the Hunting and high idle that is common after installing the Apexi and FC....:scratch:

Thanks

I don't like using the boost feature to control boost since it also controls your fuel cut. Use it at your choice.

Hunting can be fixed my raising the F/C values. For stock port engines, I usually set it to 1200 RPM and street ports 1400 RPM. Values are obviously not a set rule but usually those work. If your idle is still higher then your idle settings and won't come down, there is something else wrong. Did you cut the 4 wires when you installed the PowerFC (assuming its a LHD)?

thewird

You have two boost choices. If you go into the commander you'll be able to select them. One boost choice could be your high boost and one could be your low boost. I like to have a summer and winter setting. The winter setting has much lower duty cycle values to prevent spiking.

Within those two boost choices, you have independent control over prespool and wastegate function. Often you're fine just setting the "Pri" and "Sc" values the same, but you do have the option to tweak them individually. The duty cycle curves are coordinated with the turbo transition logic, whereas an external controller is not. As I've said before though, the Power FC is not the simplest boost controller to adjust.

I have written extensively on the idle issues. Search for threads I've started in this section.

Yes, that adds some complexity to adjusting the values. It should have been a separate fuel cut setting all along. Using the PFC is not the simplest solution, but you do get independent control of prespool and wastegate operation and you can log the duty cycle curves.

ok, i follow, however i don't see in the commander any way to 'set' what boost setting you are on, whether it's 1 or 2...

Hi again, thanks for the input,

This is a JDM import into the UK so i didn't have to cut any wires.

My manual idle set screw is about 1/4 turn out, however i need to check my dashpot functionality and also check whether the TPS voltages change when it's warmed up and i move the thermowax assembly.

Before i put in the Apexi and FC in was aware that it idled at 1100 so i think there's probably underlying issues i need to resolve before fiddling with F/C levels.

My bet is that the thermowax is still pushing the butterfly's open a little even once it's warmed up.

Instructions bro (Google it)...

https://www.rx7club.com/attachment.p...1&d=1341442351

Ya ya man, i have that in the manual, but it doesn't 'highlight' or keep which setting you're on. :)

I'll go out tomorrow to my test road and make a high boost and a low boost setting and report back. :icon_tup:

The setting its on is the one that its on when you come in and again when you leave.

thewird

Sorry, what?

Sorry lol, on my phone. The boost setting that is selected will be the one that's highlighted when you go in. When you leave that screen, the setting that's selected when you leave will be the one that is "set". Hope that makes more sense LOL.

thewird

Absolutely,

Now it is crystal clear - i think tomorrow i'll drop setting 1 down, and put setting 2 to what setting 1 is now, and then do a few runs switching between the pair to confirm. :lol:

Well, i removed the mechanical dashpot and that seems to be my car idling very well now.

I've also upped the FC settings in the idle to 1280 (as per arghx other thread) so i get a nice hold of RPM when going into neutral, and then it drops to 720rpm when idling, so it's pretty spot on!

If you have an aftermarket clutch and flywheel you do have a potential for stalling on deceleration. I personally would have just loosened it up to the point where it's not doing anything rather than take it out completely. You may have to tinker with it when the weather changes.

The closer your engine is to stock, the less temperamental it tends to be.

my fav quote