Not Boosting over 7psi

[mr299ron]

So I've recently fitted an aftermarket boost gauge to see what kind of boost the car is running.

When the car is cold, the vsv will stay closed and only allow 5/6/7psi of boost, which is normal and fine. However, once the car is warmed up, and it noticeably is a little faster, it's still only about 7-7.5psi.

I don't think there are any vaccum leaks or kinks in the line and someone has suggested my vsv might not be operating properly. Also, could my timing possibly affect the amount of boost the car makes? My timing belt was replaced before buying, and I've read that garages have set turbo'd tubbys to 5 degrees as that's some sort of standard setting..

Can anyone shed any light on why I'm possibly only seeing 7psi once the car has warmed up?

99ron

[mr299ron]

If it is in fact the VSV, and the car has gone into a "fail safe" mode where it will run on wastegate pressure, could I ensure this by disconnecting the VSV and see if the car behaves in the same way?

99ron

[tsango]

Wastegate may have weakened due to age or actuator stuck in the open position maybe??? I had a similar issue.

You could get a new wastegate but a MBC will sort this out.

[bobhatton]

If it is in fact the VSV, and the car has gone into a "fail safe" mode where it will run on wastegate pressure, could I ensure this by disconnecting the VSV and see if the car behaves in the same way?

99ron

Check for fault codes to start with, then check your cam timing then the ign timing. Stock is 10 deg btdc but if you are going to try and run more than stock boost set it to 8 deg btdc

[mr299ron]

Yeah I am currently in the process of sourcing a decent mbc. Cheers tango.

Sorry bob but I'm not following the last part of your comment. Could you explain why I should lower my timing, for more boost and power on high octane?

[mr299ron]

If it is in fact the VSV, and the car has gone into a "fail safe" mode where it will run on wastegate pressure, could I ensure this by disconnecting the VSV and see if the car behaves in the same way?

99ron

Check for fault codes to start with, then check your cam timing then the ign timing. Stock is 10 deg btdc but if you are going to try and run more than stock boost set it to 8 deg btdc

But the thing is the car is noticeably different between cold and warm. The gauge reads 5 psi when cold and 8 psi when warm. The car feels noticeably different. I honestly think it's just a bad gauge now, as the difference in figures is the same from cold to warm.

I.e on my gauge it's 5 to 8 psi

the car should be showing 7 to 10 psi

Why would the car show 5psi, then up it 8 degrees when warm? Timing out?

[mr299ron]

Come to think of it, I think there's an issue with the vsv and/or spring that releases the boost pressure.

I reckon it's a little worn and won't open up as it should.

I'm going to install an MBC and disable vsv and see what happens.

[2mad]

The vsv is a solenoid that open a hole/jet to bleed pressure away from the actuator .. if it gummed up with 20years of crap you wont make stock peek boost pressure .. my st205 gt4 was doing this .. fitted an mbc and bingo 0.8 bar to the red line ... sorted 0.9 bar at wot yay


Been watching your posts hope you sort it .

[mr299ron]

The vsv is a solenoid that open a hole/jet to bleed pressure away from the actuator .. if it gummed up with 20years of crap you wont make stock peek boost pressure .. my st205 gt4 was doing this .. fitted an mbc and bingo 0.8 bar to the red line ... sorted 0.9 bar at wot yay


Been watching your posts hope you sort it .

Hopefully this sorts it. Can I get to what allows the vsv to open and/or the hole to check how worn/full of gunk it is?

Haha hopefully dude, thanks for being helpful this far. Really appreciate it!

[masterbateson]

some one who is more of a jedi master with these engines may correct me, but you dont need to do any of those things you were talking about re the vsv if....
You are fitting a MBC.
All you do is cap off the wastegate actuator the one that your MBC is not connected to, and block off the pipe that is left loose.

Your Mbc will fit between the vacuum line off the turbo and go into the waste gate actuator.

[mr299ron]

some one who is more of a jedi master with these engines may correct me, but you dont need to do any of those things you were talking about re the vsv if....
You are fitting a MBC.
All you do is cap off the wastegate actuator that your MBC is not connected to and the pipe that was on there (the pipe on actuator you have just removed0 you block off with either a proper bung made for the job or like a lot of us will have done, rammed a bolt or a screwdriver bit into the tube to block/seal it.
hopefully someone will come along with a nice pic for you next.

Yeah I completely understand how to fit the MBC. You're basically installing your own vsv type wizardry that allows you to set the actuator to not release pressure until a certain measurement of boost. I.e 10psi.

Reading into the VSV and actuator, I honestly reckon the spring is bu88ered. I'm seeing 5psi when cold and 8psi when warm.

Now, the spring/actuator is not supposed to release until a certain pressure is hit to control boost (also linked with vsv to give you low boost when cold). So, when cold I see 5psi and when warm I see 8. So in my opinion, I think that the vsv is working correctly, however the actuator's spring/whatever is weak and is letting air escape when it shouldn't be. Thus why by passing this and letting an MBC do the job will fix it.. Correct? :S I might be wrong

[mr299ron]

Thinking about it.. I'm replacing the vsv not the wastegate spring.. How is an MBC supposed to solve this? Maybe the vsv is bu88ered then?

Does someone understand what I'm trying to say?

Cheers
99ron

[mr299ron]

Maybe the vsv is causing it to open early? Not reading boost properly?

[mr299ron]

Correction:

The T-VSV opens and bleeds off some of the pressure on the
wastegate to allow more boost, but if the sping isn't releasing correctly and not allowing me to see more boost, could this be the issue? Dodgy spring?

Feel really stupid trying to work all this out lol.

[mr299ron]

It's one of two things and I need someone to confirm:

1. The VSV opens to help bleed pressure out of the wastegate, so you don't run serious boost/boost creep and/or spike. So, if closed this means you could run say 15psi when all you want is 10. Could the wastegate constantly be releasing pressure when it's not supposed to, thus why I'm seeing 5psi when cold and 8psi when warm?

So the air is being released at 5psi when the engine is cold, and 8psi when warm.

2. Now that I've seen 1. I dont have a 2..

Im losing my marbles trying to understand all this. If you didnt know, im new to this haha

[2mad]

Ok dont have a brain meltdown mate .. my car does this with the vsv attached, when the cars warmed up it barely increases boost .. so i fitted an mbc and it fixed the problem .. 99.9% your wastegate spring is fine .. you could have a temp sensor problem but i dont know how to advise you with that ..


Basically fit an mbc and see if it cures it worked for me

[tiff_lee]

Take a breath mate!

I'm not entirely sure if you understand how the boost control circuit works or not, in some posts you seem to get in but then in others you seem confused about it.

Just to clarify (disregard the vsv for a moment), boost pressure is controlled by the wastegate actuator, once boot pressure reaches the required pressure to overcome the spring inside the actuator it will move thus opening the wastegate and regulate boost. This is how boost is controlled when cold and the vsv shut.

The vsv operation is nothing to do with boost creep or boost spikes, those are two different phenomenon which can occur with turbo setups.
So when 'hot' the VSV is open, by bleeding off a small amount of air (via the VSV) a higher boost pressure is now required to overcome the actuator spring (needs to compensate for the loss in pressure via VSV).

I'm not sure if people run a mbc with the VSV still connected or not as i'm new to 3SGTE engines (had c20lets before) but if you were to remove it from the boost control circuit and just use a mbc then whatever you set that to is what you will get. Depending on whether you use a bleed valve type or dawes device (ball and spring) you may get a boost spike then if setup wrong.

[2mad]

Nice explanation tiff_lee with the 3stge we cap of the vsv actuator port and fit an mbc to control boost

[tiff_lee]

Nice explanation tiff_lee with the 3stge we cap of the vsv actuator port and fit an mbc to control boost

Cheers mate, yeah I figured that was the case but wasn't too sure as i'm yet to even touch the engine on mine.

[2mad]

Nice explanation tiff_lee with the 3stge we cap of the vsv actuator port and fit an mbc to control boost

Cheers mate, yeah I figured that was the case but wasn't too sure as i'm yet to even touch the engine on mine.