should I be able to turn my boost down more?

[IHeartTurbo]

I have a 16g and I can only turn the boost down to about 13psi. It seems to me that I should be able to turn it down more. Am I right?

 

[96TSi_Chris]

Originally posted by IHeartTurbo
I have a 16g and I can only turn the boost down to about 13psi. It seems to me that I should be able to turn it down more. Am I right?

You def should be able to. I ran my car at 10 psi when i first got it installed w/ no mods (bought the car w/ a blown t25) and had it going at 12 for a while w/ mods.

 

[IHeartTurbo]

So do you think my mbc is faulty?

 

[96TSi_Chris]

Originally posted by IHeartTurbo
So do you think my mbc is faulty?

Is it ones of those ones w/ a spring? I know ive had tons of problems w/ mine which is spring loaded. I cant count the number ive times the spring has gotten stuck. You could take it apart and see whats up.

Just out of curiousity, why do you want it below 13?

 

[IHeartTurbo]

Originally posted by 96TSi_Chris
Is it ones of those ones w/ a spring? I know ive had tons of problems w/ mine which is spring loaded. I cant count the number ive times the spring has gotten stuck. You could take it apart and see whats up.

I took it apart and the spring doesn't seem to be stuck or anything, but it is really strong. Would putting a weaker spring in it allow me to turn it down?

Originally posted by 96TSi_Chris
Just out of curiousity, why do you want it below 13?

I get fuel cut really bad. I need a walbro 190 before I can turn it up any.

 

[TurBoGs-T]

Something isn't right here..
Are you sure that the boost gauge is reading right. 13psi should not be making you fuel cut at all. Could be the controller or you may have minor creeping. What were you running when you had the 14b, and when you had the 14b did you have the same boost gauge and boost controller???

 

[IHeartTurbo]

Originally posted by TurBoGs-T
Something isn't right here..
Are you sure that the boost gauge is reading right. 13psi should not be making you fuel cut at all. Could be the controller or you may have minor creeping. What were you running when you had the 14b, and when you had the 14b did you have the same boost gauge and boost controller???

I don't think it's creaping. It stayed right at 13 psi, and that's as high as it gets. I never ran it with a 14b on it, it had the 16g when I bought it. Before this weak, I had a huge boost leak on the outlet of the IC, but I cut the elbow off and put a 90* radiator hose and made sure everything was real tight. I haven't pressure tested it yet, but I'm pretty sure everything is tight. The really weird part is that before I fixed the leak, I would get fuel cut at 5K but now I get it at 4.5K. What the #### is wrong?

 

[TurBoGs-T]

well when i put a bigger turbo on my old car. it went 14psi without a boost controller. So that may just be what the stock boost is for it. Someone may have taken out the biss screw or whatever it is. The free mod where you get more boost. But this fuel cut situation is still confusing as hell

 

[IHeartTurbo]

Originally posted by TurBoGs-T
well when i put a bigger turbo on my old car. it went 14psi without a boost controller. So that may just be what the stock boost is for it. Someone may have taken out the biss screw or whatever it is. The free mod where you get more boost. But this fuel cut situation is still confusing as hell

Yes it is. It's pissing me off because I thought I would have fixed it when I got rid of the boost leak. One thing I just thought of: maybe the wires to my fuel pump are really bad and I need to do the rewire more then I thought?

 

[midnght]

It was the Waste Gate Solenoid Restriction that is removed for boost. The biss screw is for idle control.

 

[IHeartTurbo]

I just thought of something else. Maybe I have my mbc installed incorrectly. I think it is right, but I'd like to make sure. If it is isntalled correctly, which way do I turn it to turn the boost down. I think it's counterclockwise, but who knows.

 

[DSMeclipse4G63]

Look at it this way righty tighty and lefty loosey. When you loosen it it lessens the preasure on the spring. I believe the 16g's wastegates are set at 10 psi from the factory.
Andrew

 

[IHeartTurbo]

Originally posted by DSMeclipse4G63
Look at it this way righty tighty and lefty loosey. When you loosen it it lessens the preasure on the spring. I believe the 16g's wastegates are set at 10 psi from the factory.
Andrew

That's what I thought, I just wanted to make sure I wasn't being retarded.

I've been told to hook up a fuel pressure gauge and check it at idle a WOT to make sure that the fuel pressure increases proportionally to the boost. If it doesn't or if the fuel pressure is just really low then that might cause it right?

 

[DSMeclipse4G63]

My fuel preasure raises to the max with a blip of the throttle. Or cl;ose to it. Fuel pressure raises slightly with throttle... it has more to do with throttle, rpm and such being as though we have a mechanical return fuel system. try taking the boost controller off and see if you get 10 psi or so and if you do then its the mbc that isnt able to go down. If anything low fuel pressure would limit boost.
Andrew

 

[psychlow]

IHeartTurbo, where was your boost leak? Are you sure you don't have any more boost leaks?

 

[IHeartTurbo]

Originally posted by psychlow
IHeartTurbo, where was your boost leak? Are you sure you don't have any more boost leaks?

It was on the outlet of my my smic. I cut the 90* bend off and put a 90* radiator hose on there and connected it to the next piece of hose with some exhaust piping. I know there is no leak there, but I guess there could be one somewhere else. I haven't pressure tested it since I fixed it and I'm not really sure why, but I'm gonna do that tomorrow among many other things. I'm fairly confident that I don't have a boost leak tho.

 

[psychlow]

Yeah, maybe. 13PSI sounds a little low for fuel cut, though. IMHO. Most people hit it in the upper teens or even twenties with 16Gs.

 

[IHeartTurbo]

Originally posted by psychlow
Yeah, maybe. 13PSI sounds a little low for fuel cut, though. IMHO. Most people hit it in the upper teens or even twenties with 16Gs.

Which is why I think I need to rewire my fuel pump cuz I think it's a lot worse then it should be.

 

[psychlow]

Well, here's the thing:

Fuel cut is reached when the ECU sees a certain amount of air going into the engine.

It doesn't really care if the fuel pump isn't putting out enough fuel. If the fuel pump was going out, it'd still allow you to run, albeit lean, until your engine went bye-bye.

 

[IHeartTurbo]

So I'm getting too much air? How can that be? I really don't understand this as well as I thought I did.

 

[IHeartTurbo]

Another thing I don't think I mentioned and it might be relevant. It takes longer to start up my car now then it did before, like about 5-6 seconds. Then, when it does start up, I can't touch the gas at all for about 10 seconds or it will stall. Well, if I floor it, it will stall, but if I just press it down a little bit and hold it there, it will bog right down to just a couple hundred RPMs then rev up like it should. What could this be and could it be related?

 

[psychlow]

It's not exactly that your engine is actually "getting" too much air, but that your ECU is just reading too much air.

What happens, is the air is sucked past the MAF sensor, so the engine reads that the air is going into the engine. Instead, this "metered" air gets vented to atmosphere by a boost leak before it makes it to the engine.

Thus, your ECU thinks you're building too much pressure, so it fuel cuts, even though you're only pushing 13PSI. You're taking in enough air to create much more pressure, but your pressure is getting bled off.

This also has the effect of not opening your wastegate at the right turbo speed. Your turbo keeps spinning faster and faster until it finally creates enough pressure to open the wastegate. This shortens the life of your turbo, as it's spinning faster than it was originally designed for.

Boost leaks are the plague to turbo cars' owners. (See my signature.) :thumbdown

(By the way, if you'd like to lower the PSI your turbo makes, just take off the MBC and connect the boost reference hose straight to the wastegate. Most MBC's have a bleeder hole which bleeds some boost to atmosphere, resulting in a higher set pressure.)

 

[IHeartTurbo]

Originally posted by psychlow
It's not exactly that your engine is actually "getting" too much air, but that your ECU is just reading too much air.

What happens, is the air is sucked past the MAF sensor, so the engine reads that the air is going into the engine. Instead, this "metered" air gets vented to atmosphere by a boost leak before it makes it to the engine.

Thus, your ECU thinks you're building too much pressure, so it fuel cuts, even though you're only pushing 13PSI. You're taking in enough air to create much more pressure, but your pressure is getting bled off.

This also has the effect of not opening your wastegate at the right turbo speed. Your turbo keeps spinning faster and faster until it finally creates enough pressure to open the wastegate. This shortens the life of your turbo, as it's spinning faster than it was originally designed for.

Boost leaks are the plague to turbo cars' owners. (See my signature.) :thumbdown

Wow, that's the best description of it that I have read since I've been here. Thanks, it actually makes sense now. But, lets say I don't have aboost leak, what else could cause it?

 

[psychlow]

Originally posted by IHeartTurbo
Wow, that's the best description of it that I have read since I've been here. Thanks, it actually makes sense now. But, lets say I don't have aboost leak, what else could cause it?

No problem, I'm glad that all made sense.

If it's not a boost leak, the only other thing I could say it'd be is either:
-Bad/Malfunctioning ECU
-Bad MAF (although I've never heard of one reading too high)
-Bad barometric pressure sensor (part of the MAF)

I'd suspect a bad barometric pressure sensor first, as the ECU figures where to fuel cut based on a given amount of air from a formula derived from the outside barometric pressure. If it thinks the barometric pressure is very low, I'm thinking it may perceive a low amount of airflow as 'too much' (but don't quote me on that, as I'm don't have any firsthand experience on the subject and I'm just making guesses at this point.)

Do you have a logger? If so, do you have any logs you can post?

 

[IHeartTurbo]

Originally posted by psychlow
No problem, I'm glad that all made sense.

If it's not a boost leak, the only other thing I could say it'd be is either:
-Bad/Malfunctioning ECU
-Bad MAF (although I've never heard of one reading too high)
-Bad barometric pressure sensor (part of the MAF)

I'd suspect a bad barometric pressure sensor first, as the ECU figures where to fuel cut based on a given amount of air from a formula derived from the outside barometric pressure. If it thinks the barometric pressure is very low, I'm thinking it may perceive a low amount of airflow as 'too much' (but don't quote me on that, as I'm don't have any firsthand experience on the subject and I'm just making guesses at this point.)

Do you have a logger? If so, do you have any logs you can post?

Nope, no logger. I could just switch in someones MAF that I know works to see if that is the problem couldn't I? And lets say the MAF or whatever that other thing is does turn out to be bad, would you suggest getting a GM MAF and translator?