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Rb25 Won't Hold Boost

zinkrb250

By zinkrb250,
in Engines & Forced Induction

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zinkrb250 Enthusiast

zinkrb250

Posted
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motor: rb25det

upgrades: hks gtrs turbo, power fc, 3" turbo back, power FC boost controller, 555cc injectors, tomei poncams, Pod filter

Problem: Whenever i take the car for a cruise... I stomp on it... boost climbs to approximately 10psi and as soon as it reaches 10psi, the boost starts to fade back down to 0 psi.... almost like the wastegate is stuck open.... it will remain at 0 psi until i let off the throttle and/or push in the clutch... then the pressure will rise back to 10psi and leak back to 0

Idea: I've got the correct vacuum line going from the boost solenoid to the waste gate... but the other line on the boost solenoid which is supposed to go to the cold pipe, is hooked up to the metal tubing that runs underneath the charge pipe and leads to the throttle body plate... can't remember if it's the "com" port or the "no" port on the actuator... but i have read that it is supposed to connect to the cold pipe before the throttle body, via a nipple welded onto the cold pipe

Lets hear the ideas/suggestions

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BezerkR32 Veteran

BezerkR32

Posted
Posted

Did you use that silicone hose to plumb to the actuator? if so, put normal vacuum hose on and try it. Otherwise test actuator with compessed air. could be tear in diaphram.

motor: rb25det

upgrades: hks gtrs turbo, power fc, 3" turbo back, power FC boost controller, 555cc injectors, tomei poncams, Pod filter

Problem: Whenever i take the car for a cruise... I stomp on it... boost climbs to approximately 10psi and as soon as it reaches 10psi, the boost starts to fade back down to 0 psi.... almost like the wastegate is stuck open.... it will remain at 0 psi until i let off the throttle and/or push in the clutch... then the pressure will rise back to 10psi and leak back to 0

Idea: I've got the correct vacuum line going from the boost solenoid to the waste gate... but the other line on the boost solenoid which is supposed to go to the cold pipe, is hooked up to the metal tubing that runs underneath the charge pipe and leads to the throttle body plate... can't remember if it's the "com" port or the "no" port on the actuator... but i have read that it is supposed to connect to the cold pipe before the throttle body, via a nipple welded onto the cold pipe

Lets hear the ideas/suggestions

zinkrb250 Enthusiast

zinkrb250

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  • Author
Posted (edited)
what bov are you using?

still using the OEM BOV... wondering if i need to adjust the duty cycle on the PFC boost functions?

using OEM vacuum hose... this stuff wouldn't collapse just yet... i really do think it has something to do w/ how i've got the intake charge pipe vacuum line hooked up

Edited by zinkrb250
zinkrb250 Enthusiast

zinkrb250

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tested the wastegate... works fine...

Now when the car hits approximately 10psi it cuts off (boost press. drops/engine shuts off) only for a second... then it kicks back on as soon as it drops below 10psi... and it will keep doing this as long as my foot is on the pedal and we're at 10psi of boost...

The car literally feels like it's shutting off - then on - then off - then on...

I've got it checked on the PowerFC option "yes" that i've got the boost controller kit....

I tried turning that off and i boosted up to 15psi before i let off the gas... it didn't do any of the on/off/on/off stuff...

So what does this tell me?

zinkrb250 Enthusiast

zinkrb250

Posted
  • Author
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the map sensor is T'd off of the vacuum line going to my Fuel press. reg.... it reads boost fine on my hand controller...

I was missing the factory boost solenoid and harness when i installed the rb25 into my s14 so i had to hardwire a 12v. source to the AFM 12v source... then i ran the earth wire from the apexi solenoid to pin 25 on the efi harness.... according the the rb25 wire schematics, pin 25 is the boost solenoid control...

I can hear the apexi solenoid click whenever i turn the ignition to "on"...

I get a 12v reading whenever i check for power on the apexi solenoid

zinkrb250 Enthusiast

zinkrb250

Posted
  • Author
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So its setup like in the diagram.

post-12828-1151529964.jpg

Correct... The wastegate vacuum is running to the "COM" port (short length of hose as recommended in the instructions)

but i don't have a nipple on my intercooler piping (it's the FMIC Hybrid kit)... so instead of having the "NO" port vacuum line running before the throttle body, it's attatched to the throttle body plate that attatches to the intake plenum...

here's a picture of what i'm talking about.... This is and old one before i installed the apexi solenoid but it'll still give you the right impression....

The vacuum circled in the picture is where i've got the "NO" vacuum line plumbed....

e6fd5f70copy.jpg

according to the apexi instructions it should be before your throttle body on the cold side of the intercooler piping

rob82 Mentor

rob82

Posted
Posted
Correct... The wastegate vacuum is running to the "COM" port (short length of hose as recommended in the instructions)

but i don't have a nipple on my intercooler piping (it's the FMIC Hybrid kit)... so instead of having the "NO" port vacuum line running before the throttle body, it's attatched to the throttle body plate that attatches to the intake plenum...

here's a picture of what i'm talking about.... This is and old one before i installed the apexi solenoid but it'll still give you the right impression....

The vacuum circled in the picture is where i've got the "NO" vacuum line plumbed....

e6fd5f70copy.jpg

according to the apexi instructions it should be before your throttle body on the cold side of the intercooler piping

Cant remember if you can get the duty cycle reading on the hand controller but see if you can get a multimeter that measures it. Then you will be able to see if you have a mechanical problem or an electrical problem.

zinkrb250 Enthusiast

zinkrb250

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Yes.. On the H/C under settings - boost - you have about 5 different boost settings to choose from.... next to each boost setting you've got the duty cycle setting and then next to each duty cycle setting is the number 255...

right now i've just got it on the lowest setting of .5 mmhg? and then 48 duty cycle....

These were the original numbers already in the pfc from apexi

Wouldn't i have to be driving the car to use the multimeter to see when or if the solenoid was opening?

r33_racer Grand Master

r33_racer

Posted
Posted

umm if its after then that might be your problem, you want it before the butterfly plate so its on the charge pipe side...not the plenum side. As typically you would have it off the turbo charger housing or somewhere around there on your intercooler piping. I believe that for quickest response you try and set it at a point closest to the pressure source...which is your compressor outlet.

rob82 Mentor

rob82

Posted
Posted (edited)
Yes.. On the H/C under settings - boost - you have about 5 different boost settings to choose from.... next to each boost setting you've got the duty cycle setting and then next to each duty cycle setting is the number 255...

right now i've just got it on the lowest setting of .5 mmhg? and then 48 duty cycle....

These were the original numbers already in the pfc from apexi

Wouldn't i have to be driving the car to use the multimeter to see when or if the solenoid was opening?

Yes thats right there are four boost setting each with a boost pressure set level and a starting duty cycle. The way it works is you take a stab at the base duty cycle from here the PFC works out wether or not it is above or below the boost set point and decides if it needs to increase or decrease the duty cycle to achieve the desired boost level, it does this throughout the entire rev range at a frequency of about 40Hz from memory. That means it can calculate a duty cycle 40 times per second.

Now what happens if you set a high base duty cycle and a low boost setting is it spikes up using the base duty cycle guess and then it sees that its current boost point is too high for the desired boost level and it pulls the boost out by reducing the duty cycle. Remeber it can only go as low as the base wastegate spring pressure if it is less than this at any point the you have a mechanical problem. A good test would be to take the boost solenoid out of the equation and see if it holds wastegate pressure.

The setting you have in there of 0.5kg/cm2 = about 7psi which is probably pretty close to wastegate spring pressure. So if your duty cycle of 48 is spiking to say 15 psi and you are trying to run 15 pound then you need to put in a boost setting of 1.05kg/cm2 = 15psi.

Edited by rob82
zinkrb250 Enthusiast

zinkrb250

Posted
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Yes thats right there are four boost setting each with a boost pressure set level and a starting duty cycle. The way it works is you take a stab at the base duty cycle from here the PFC works out wether or not it is above or below the boost set point and decides if it needs to increase or decrease the duty cycle to achieve the desired boost level, it does this throughout the entire rev range at a frequency of about 40Hz from memory. That means it can calculate a duty cycle 40 times per second.

Now what happens if you set a high base duty cycle and a low boost setting is it spikes up using the base duty cycle guess and then it sees that its current boost point is too high for the desired boost level and it pulls the boost out by reducing the duty cycle. Remeber it can only go as low as the base wastegate spring pressure if it is less than this at any point the you have a mechanical problem. A good test would be to take the boost solenoid out of the equation and see if it holds wastegate pressure.

The setting you have in there of 0.5kg/cm2 = about 7psi which is probably pretty close to wastegate spring pressure. So if your duty cycle of 48 is spiking to say 15 psi and you are trying to run 15 pound then you need to put in a boost setting of 1.05kg/cm2 = 15psi.

Well i took the solenoid out of the equation and it held a steady 10-11psi ....

So does this mean (on the pfc h/c) that on boost setting #1 at .5kg/cm2 i should lower duty cycle from (factory) 48 to....?????? what? I have no idea how this thing works

rob82 Mentor

rob82

Posted
Posted
Well i took the solenoid out of the equation and it held a steady 10-11psi ....

So does this mean (on the pfc h/c) that on boost setting #1 at .5kg/cm2 i should lower duty cycle from (factory) 48 to....?????? what? I have no idea how this thing works

So that means that you have a 10psi actuator.

If you want to run 15psi then put in 1.05kg/cm2 for boost and try about 50% duty cycle. If the boost shoots over 15psi but then drops back down high in the rev range reduce your duty cycle by 5% then try again. Do this for each boost level you desire remeber the high the boost level the more base duty cycle it will need and vice versa for less boost.

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