Boost leak test question?

[Flybiyou]

Hope you are ok man. My dad just had a heart attack about 6 months ago scared the shit out of me. Well if im not the first at least like you said a good read about places that can leak. What do you think about my story think it matchs with whats happening.

 

[steve]

What do you think about my story think it matchs with whats happening.

Sure, it's easy for the EGR to leak from the intake manifold to the exhaust. It shouldn't but it doesn't take anything more than some carbon buildup on the valve to let it leak. That's why I keep saying to take the EGR valve off and clean it. You can check or replace the EGR gasket while your there and make sure that the valve doesn't leak when you put it back on.

Steve

 

[Flybiyou]

Well I tryed cleaning the Egr but nothing it is the same. So I blocked it off and did the test again it held fine no air coming from the egr hole. BUT I found all 4 lower injector seal's leaking. It was coming out good to didnt need soap and water to tell. I cant tell if anything else it leaking though till I fix the seals. I already ordered them and I have a FPR coming with all the stainless steel lines so I can just change out the bottom seals while I am there.
I have been tearing my car apart getting ready to add my new setup and have found that even though these car's are a PITA to work on they are simple to work on . I would also suggest anyone who has not done a boost leak test to do one. I found 7 Leaks I never knew of. Injector seal's//both intercooler couplings// BOV flange leaked at weld// Bov leaked at the gasket///Intercooler pipe coupling small tear//EGR was stuck half open.
I will continue to test this system till I find all leaks. Thanks again for all the help
AJ

 

[power=dsm]

so everytime you do a boost leak test you have to make sure your 30* after tdc? How come i never heard of this before

 

[Flybiyou]

so everytime you do a boost leak test you have to make sure your 30* after tdc? How come i never heard of this before

I didnt really know about it as well it dosent say anything in the vfaq or in the tech articals.
help me out alot though.

 

[steve]

How come i never heard of this before

Because people expect you understand that at least one set of valves in each cylinder needs to be closed for a pressure test to work. Since most people don't seem to own a manual, know what the cam specs are, or how to figure the duration of overlap, I started suggesting they use 30 degrees as a simple rule of thumb.

Steve

 

[FORMONTOYA]

so everytime you do a boost leak test you have to make sure your 30* after tdc? How come i never heard of this before

I don't know why it is not mentioned in the VFAQ, but the reason behind it is so you have no valve overlap. Meaning that none of the valves are open. You want to make sure the valves are closed so you are not leaking into the combustion chamber through the intake valves and then out through the exhaust valves (or past the rings, but that is another test). At roughly 30 degrees ATDC all the valves are closed so that is one potential "boost leak" that you do not have to deal with.

Of course when people write up tech articles they are doing it from memory and sometimes things get left out/forgotten. And as stated, you are expected to know the "basics" of whatever you are trying to do.


Jim

 

[oldman]

I don't know why it is not mentioned in the VFAQ, but the reason behind it is so you have no valve overlap. Meaning that none of the valves are open. You want to make sure the valves are closed so you are not leaking into the combustion chamber through the intake valves and then out through the exhaust valves (or past the rings, but that is another test). At roughly 30 degrees ATDC all the valves are closed so that is one potential "boost leak" that you do not have to deal with.

Not quite. Valve overlap means both intake and exhaust valves are open at the same time, this only happens in between the end of exhaust stroke and beginning of intake stroke, the purpose of 30* after TDC is to avoid just that. It is not necessary nor is it possible to close all valves in all four cylinders at the same time, there will always be something open, the key is to avoid both opening in the same cylinder at any given time. Since valve overlap only happens 4 times in each engine cycle for a relatively short period of time, I suspect the reason for this not being mentioned more often (steve and I actually have mentioned it many times) is probably because you're less likely to hit valve overlap than not, usually a little bump from the starter should fix this.

 

[FORMONTOYA]

Not quite. Valve overlap means both intake and exhaust valves are open at the same time, this only happens in between the end of exhaust stroke and beginning of intake stroke, the purpose of 30* after TDC is to avoid just that. It is not necessary nor is it possible to close all valves in all four cylinders at the same time, there will always be something open, the key is to avoid both opening in the same cylinder at any given time. Since valve overlap only happens 4 times in each engine cycle for a relatively short period of time, I suspect the reason for this not being mentioned more often (steve and I actually have mentioned it many times) is probably because you're less likely to hit valve overlap than not, usually a little bump from the starter should fix this.

Thanks for the clairification. I knew that it meant that they, intake/exhaust valves, were open at the same time in a cylinder. However, I did not know there is NOT a spot where all valves are closed. Although it makes sence that a set of valves will be open at any given time.


Jim

 

[power=dsm]

thanks for the info

 

[oldman]

However, I did not know there is NOT a spot where all valves are closed. Although it makes sence that a set of valves will be open at any given time.

Jim, you mis-understood me. Both intake and exhaust valves are closed during both the compression and power strokes of that particular cylinder, it's just impossible to put all cylinders in compression or power stroke at the same time.

 

[FORMONTOYA]

Jim, you mis-understood me. Both intake and exhaust valves are closed during both the compression and power strokes of that particular cylinder, it's just impossible to put all cylinders in compression or power stroke at the same time.

I understood what you meant, I guess I just didn't reply that well previously. Sorry.

Thanks again

Jim

 

[oldman]

No problem.

 

[Flybiyou]

Well I guess this thread help not only me out but others to understand the right way to test foir leaks.

I found out that I was missing a bolt in the middle of the fuel rail. I got one from the junk yard and went to put it in and found the guy that put my 6-bolt in broke the bolt off in the head . This look's like it will be a PITA to get out. I havbe never used a EZ OUT im sure it's not hard the thing that worrys me is that I might not be able to get the drill in there. I torqued the two other bolts to 9lbs and the leak was slower I was going to torque it down a little more but I have heard people talk about there rail snaping. I am still going to put the new seals in but so far it will hold 22psi then fall to 15psi in 8seconds 15psi to 10 psi in 13 seconds and then fall really sl;ow to 3psi in 42seconds. I keep pumping the air in while a friend cheaked for other leaks nothing except I fell\hear alittle by the exhaust ports and one leak by the intake manifold to head really small though spayed it with soap and water and the bubble was tiny. I could also hear air hissing slightly when I removed the oil cap and stuck my ear by it. Could of just been the injectors leaking making it sound like it was coming from the head. Im going to turn ther motor over again and see if I can get the slight hissing from the exhasut ports to stop maybe they are cracked open a tad.

So for what the engine is holding for pressure now bad is the leaking and does it have to hold completly for what ever pressure you run. Im not looking for perfect just better than acceptable. Thanks again Steve & Oldman any words for this post maybe a easy way to get that bolt out easy without taking off the head or do you think the two bolt should be fine. It has been like that for 35,000 mile's and never leaked fuel. Let me know.