Boost isn't Steady

[low_psi]

For Spud:

Boosted 9.5 steadily for a week or so and then it started to leak off after peaking at 9.5psi. Reset the ECU, got rid of the hesitation issue. Still peaking and then leaking off after hitting 9.5psi.

Why did the car all the sudden start leaking boost? Is anyone holding higher boost steadily? We will be checking all the vaccum lines tomorrow, so is there anything else to do?

I know he posted this already, but I'm looking for other suggestions.

 

[SuperSpud]

I know Im not... oh wait... lol

 

[unwrittenLaw]

i'll bump this because i'm curious too...

 

[perfworks]

For Spud:

Boosted 9.5 steadily for a week or so and then it started to leak off after peaking at 9.5psi. Reset the ECU, got rid of the hesitation issue. Still peaking and then leaking off after hitting 9.5psi.

Why did the car all the sudden start leaking boost? Is anyone holding higher boost steadily? We will be checking all the vaccum lines tomorrow, so is there anything else to do?

I know he posted this already, but I'm looking for other suggestions.

How do you know its leaking boost?? Do you hear it??
It could be just spiking. Boost pressure will equal out in the manifold sometimes depending on throttle position, load and atmospheric changes. Also pressure drop in the system. The turbo may not be able to hold the boost. Sometimes also with internal wastegates the spring pressure tightens up after the flapper has opened.
There are many things it could be. You need to get a reference from the boost gauge in different spots after the turbo to see what is going on for sure. And are you using a stock recirculating valve??
i suggested to many on this board already that have the MSP to get the bosch recirculating valve to upgrade because sometimes the spring tension in the stock unit will flutter

 

[SuperSpud]

Re: Re: Boost isn't Steady

How do you know its leaking boost?? Do you hear it??
It could be just spiking. Boost pressure will equal out in the manifold sometimes depending on throttle position, load and atmospheric changes. Also pressure drop in the system. The turbo may not be able to hold the boost. Sometimes also with internal wastegates the spring pressure tightens up after the flapper has opened.
There are many things it could be. You need to get a reference from the boost gauge in different spots after the turbo to see what is going on for sure. And are you using a stock recirculating valve??
i suggested to many on this board already that have the MSP to get the bosch recirculating valve to upgrade because sometimes the spring tension in the stock unit will flutter

yes, he means spiking.. (Its my car)... it goes to 9.5psi up until around 4500, then drops down to 7'ish....
when I downshift from 5th to 3rd, it goes way down to like, 5-6psi, which is lower than it registered when I got my car.... and boost holds right at 9.5 in 5th, no spiking...

 

[boostisgood]

With a manual boost controller, you will find boost to be higher in the higher gears, If its 7.5 in 3rd gear, you will see, and hold the 9.5 in a higher gear. I truly cannot remember the explanation, Ill try to find it today, in my SCC mag that referenced it.

 

[perfworks]

Re: Re: Re: Boost isn't Steady

yes, he means spiking.. (Its my car)... it goes to 9.5psi up until around 4500, then drops down to 7'ish....
when I downshift from 5th to 3rd, it goes way down to like, 5-6psi, which is lower than it registered when I got my car.... and boost holds right at 9.5 in 5th, no spiking...

Ive seen this happen first hand when you downshift. There really isnt a load and the high rpm allows the air to flow so measured boost will be less. Untill you floor it again but then it really wont pin to a higher psi anyway till you hit 4rth

 

[SuperSpud]

so if I want to set it at 9.5 psi,, I should let it spike higher? and then let it come down to 9.5???

so it would spike at like 12, then stay at 9.5?? is that what your saying?

 

[perfworks]

so if I want to set it at 9.5 psi,, I should let it spike higher? and then let it come down to 9.5???

so it would spike at like 12, then stay at 9.5?? is that what your saying?

Again spud there are alot of different reasons why you are spiking. It is evident when you initially go into WOT. The process includes how well the engine can process the air it is given.
Then other factors take place like pressure loss and spring tension in the control devises. The MSP has a very small turbo to begin with that can only pump so much efficiently at the higher RPM levels without the stock induction " bypassing" it

 

[unwrittenLaw]

I'm just a bit worried about spiking to 12-13 on a constant basis...

 

[yashooa]

Hmm

Mine hits 12 for about 2 secs then drops to 11 and then stays on 10 until shift. I had to play with the MBC fot a few days but for the last couple weeks it has ran great not one bit of boost loss.

 

[SuperSpud]

I'm just a bit worried about spiking to 12-13 on a constant basis...

as am I

 

[kwiktsi]

so if I want to set it at 9.5 psi,, I should let it spike higher? and then let it come down to 9.5???

so it would spike at like 12, then stay at 9.5?? is that what your saying?

Dude- you are not spiking- a spike is right to xx psi than instantly falling to whatever. These cars go to a higher psi and hold it there for a while, then drop as RPM's increase. If I have to explain to anyone else that it is caused by a bad turbo combined with a weak WG spring and a 4 banger revving to 7k, I will lose it .

You have IM'ed me several times about this and I told you it is the nature of the car. If you don't want the boost to ever drop or fluctuate, get a bigger turbo, extrenal gate and an electronic controller. It is not a boost leak with the car, we have been through this .

My car has a damn $500 Blitz controller and it always drops around 2-3 psi from peak (and I tightened my wastegate!!) and is as much as 4-5 psi higher if I roll on it in the higher gears until the load lessens.

I don't know the reason it didn't do it at first and does now- could be the wastegate spring loosening up a bit, air density, etc. We have gone through this .. There are times where mine will hold solid and times it will drop also- again, there are a lot of variables to be considered.

Joe

 

[kwiktsi]

With a manual boost controller, you will find boost to be higher in the higher gears, If its 7.5 in 3rd gear, you will see, and hold the 9.5 in a higher gear. I truly cannot remember the explanation, Ill try to find it today, in my SCC mag that referenced it.

It is due to engine load being greater and longer duration in the higher gears. It is not just MBC's a lot of EBC's do it too- my Blitz DSBC does it too.
Joe

 

[SuperSpud]

Dude- you are not spiking- a spike is right to xx psi than instantly falling to whatever. These cars go to a higher psi and hold it there for a while, then drop as RPM's increase. If I have to explain to anyone else that it is caused by a bad turbo combined with a weak WG spring and a 4 banger revving to 7k, I will lose it .

You have IM'ed me several times about this and I told you it is the nature of the car. If you don't want the boost to ever drop or fluctuate, get a bigger turbo, extrenal gate and an electronic controller. It is not a boost leak with the car, we have been through this .

My car has a damn $500 Blitz controller and it always drops around 2-3 psi from peak (and I tightened my wastegate!!) and is as much as 4-5 psi higher if I roll on it in the higher gears until the load lessens.

I don't know the reason it didn't do it at first and does now- could be the wastegate spring loosening up a bit, air density, etc. We have gone through this .. There are times where mine will hold solid and times it will drop also- again, there are a lot of variables to be considered.

Joe

I done got told lol

 

[Brian MP5T]

Re: Varing Boost

Hey, I read the whole thread and about your boost drop...

Are you running a stock Mazdaspeed or have you tweaked it. The reason I ask is that if you use the stock intergrated wastegate at higher than intended pressures you will encounter a " Skate " problem. That is to say the wastegate will have a higher chance for inconsistent max boost ( The Boost Needle Might Skate ). If this is the case and you want better control I have two solutions.

1. Expensive, Swap to a Garrett T-25 without a wastegate and weld a Proper wastegate like Tial 35mm to the manifold.

2. Less Expensive Lock the stock wategate Actuator and then ... like above... get a proper wastegate.

When playing with Pistons under boost, the more loose your boost pressure is , the harder it will be for your fuel management system to maintain Stoych Balance. Hope it helped./members/Brian MP5T/mazda mp5t - zoom zoom - (1).jpg

 

[kwiktsi]

I done got told lol

lol...
Joe

 

[kwiktsi]

Re: Re: Varing Boost

Hey, I read the whole thread and about your boost drop...

Are you running a stock Mazdaspeed or have you tweaked it. The reason I ask is that if you use the stock intergrated wastegate at higher than intended pressures you will encounter a " Skate " problem. That is to say the wastegate will have a higher chance for inconsistent max boost ( The Boost Needle Might Skate ). If this is the case and you want better control I have two solutions.

1. Expensive, Swap to a Garrett T-25 without a wastegate and weld a Proper wastegate like Tial 35mm to the manifold.

2. Less Expensive Lock the stock wategate Actuator and then ... like above... get a proper wastegate.

When playing with Pistons under boost, the more loose your boost pressure is , the harder it will be for your fuel management system to maintain Stoych Balance. Hope it helped./members/Brian MP5T/mazda mp5t - zoom zoom - (1).jpg

Well said..

Nice car BTW. How's it run ? Any #'s on it?
Joe

 

[Tex]

Hey Perfworks,

Where does one buy this Bosch recirculating valve? I went to the Bosch web site, and could find no such animal.

Thanks.

 

[low_psi]

are there no options regarding the replacement of the stock WG's spring, to a stiffer one? i'm not familar with which turbos use the same wastegates.