Boost leak test leaking air into valve cover on my rebuilt engine with 50 miles

[TurboSpider]

Just had my engine rebuilt at a local Napa machine shop. The head has all new valve seals put in and a few valve guides replaced that were out of spec. Bottom end had the cylinders bore .20 over with new wiseco pistons. The reason I had the engine rebuilt in the first place is because when I boost leak tested it, it was doing the exact same thing. Leaking air out side port on valve cover. It also was going through wide band sensors left and right and smoking some under hard boost and sometimes at idle.

So I get the engine back from the machine shop and put it all back together. They assembled the head and cams. I basically bolted head onto block and put everything else back together and put it back in. Start it up and car idles kinda rough with A/F all over which may just be due to the idle. I drove it around for the first 50 miles breaking in the engine. I then started to get ready to tune it but first did a BLT to make sure everything was ok. I put the BLT on the turbo and heard air coming out the valve cover side port.

I did some research and saw it may be normal for the turbo to leak some at the seals when it does not have oil pressure. I then moved BLT to throttle body elbow. Same result, air coming out side port on valve cover. Did some more research and saw the engine should be at 30 degrees ATDC to prevent valve overlap. Tried turning engine around to where I think 30 ATDC is and still same result.

So what my next steps should be. Should I drive the car some more to break the engine in more and maybe get better engine sealing? Before I had the engine rebuilt, i did compression tests which were all good, did a cylinder leak down test which was also within spec but one was a little lower than the other. Am I missing something here? I just find it hard to believe after all I have had done with this engine it is still doing the same thing.

Also adding, i disconnected and capped off the line that goes from the intake manifold to the valve on back of valve cover so its not leaking through that line into the valve cover. and also the vacuum line that goes from BOV to intake. I left the line that comes off the small nipple that goes to my FPR hooked up

 

[dwb]

Blow-by, valve seats, valve guides/seals, and PCV valve all can cause air to leak into the crankcase.

I'd be curious what you get for leak down and compression test now after rebuild.

 

[Vegas Smith]

My old engine had almost perfect leakdown and compression results and still leaked air on a BLT. Not saying it's right or wrong.

 

[TurboSpider]

Thats kinda how mine was before I sent it out to be rebuilt. Compression was all within 10% of one another. My leakdown test was ok with with all being in the recommended ranges with one cylder being a little lower than others on pressure holding. I was originally having oil dripping into exhaust mainfolt and leaking out exhaust manifold gasket. Stuck a scope in the exhaust ports and two of the valve seals appeared to be leaking.

Vegas Smith, did you have any idling or drivability issues on that old engine?

Blow-by, valve seats, valve guides/seals, and PCV valve all can cause air to leak into the crankcase.

I'd be curious what you get for leak down and compression test now after rebuild.

I'm gonna run these tests on the rebuilt engine and see what I get

 

[Xarzor]

I'm curious to know if this is normal. I pulled my engine, installed head studs, replaced all the gaskets and seals. Did a leak test and heard the air running though the crank case. Thought I messed something up. Called all my mechanic friends and couldn't get a straight answer. Even from one friend who builds diesel engines for a living.

 

[DSMPT]

Assuming you don't have any issues, this is normal that you hear the air coming from crank case if you do the boost leak test by charging the air from the turbo inlet or/and with intake cam installed.

I did some research and saw it may be normal for the turbo to leak some at the seals when it does not have oil pressure. I then moved BLT to throttle body elbow. Same result, air coming out side port on valve cover. Did some more research and saw the engine should be at 30 degrees ATDC to prevent valve overlap. Tried turning engine around to where I think 30 ATDC is and still same result.

The air goes into crank case through turbo drain pipe. And if you had intake cam/caps installed, some intake valves would still have been open slightly.

 

[TurboSpider]

Ok this is good to know then, from what all I saw on here people were putting air into the engines and they were just holding it all in. I am testing it with the camshafts installed and testing at throttle body elbow, so I guess that is why it is leaking then. Pretty much leaks down to about 6 psi after a few seconds. I can get it to hold air a little longer if I cap off both PCV and air inlet on left of valve cover but then it starts leaking out the top of my FPR (adjustment screw) which I have seen is normal as there is no fuel running through it to help pressurize the other side. Kinda hard to tell how long it holds becuase I don't have a gauge on my BLT and am using the air fill valve gauge which doesn't register changes on the gauge unless you remove it and then reinstall it onto shrader valve if that makes any sense. I know if I wait about 20 seconds after pressurizing it to 20 psi, it is down around 3-6 psi when I check it again because of the air leaking out valve cover inlet.

I still am going to perform a compression and leak down test just to see the health of the engine since the rebuild and from what I am reading should be broken in enough after 60 miles. I guess if everything looks ok there, my idle issue is just tuning issue that I am having. Its definitely running a little rich at idle. Tried changing over to SD and it seemed to idle a little better but the tables must need adjusted as it is running very rich under mild boost. The idle issues is why I decided to BLT because everyone says that is the first thing to do when its idling or driving strange.

 

[Vegas Smith]

If you search BL tests you’ll get people saying it took them 5 minutes for the boost to leak etc. That’s never been the case for me, and I’ve had multiple healthy engines to go off of. Not saying I’m a master engine guru but just stating my experiences.

 

[dwb]

The air goes into crank case through turbo drain pipe.

Is this opinion or fact? I think if this were true you would be blowing oil into your intake under vacuum conditions and then pressurizing your CC under boost. The turbo oil seals should prevent such a condition.

And if you had intake cam/caps installed, some intake valves would still have been open slightly.

Blow-by, intake valve stem seals/guides, and exhaust valve/seats are the concern here.

 

[1990TSIAWDTALON]

I would break that engine in a bit more. Go run it with some varying loads on it. Get into boost if you can and make sure that the rings are seated. 50 miles isn't much. Put 300-500 on it and don't be afraid to drive her. I boosted my new engine within the first 100 miles at 32 psi. She runs good, no oil consumption, blow by, or excessive CC pressure. I always run the first 100 miles as initial break-in, change the oil and do another 3-400 and consider it THEN, broken in and all things sealed up to the best of their abilities.

 

[Vegas Smith]

Is this opinion or fact? I think if this were true you would be blowing oil into your intake under vacuum conditions and then pressurizing your CC under boost. The turbo oil seals should prevent such a condition.

Blow-by, intake valve stem seals/guides, and exhaust valve/seats are the concern here.

Probably fact. FP once explained to me that some turbos seals are "dynamic" in that they seal when the engine is running but will leak air into the engine on a BLT.

 

[DSMPT]

Is this opinion or fact?

Fact.

I think if this were true you would be blowing oil into your intake under vacuum conditions and then pressurizing your CC under boost. The turbo oil seals should prevent such a condition.

Wrong. @Vegas Smith already said above. You have never heard bubbling sound from oil drain tube while running a BLT by charging the air from the turbo inlet? This is why people tell you to charge the air from inlet of lower intercooler pipe instead of the turbo compressor housing inlet.

Blow-by, intake valve stem seals/guides, and exhaust valve/seats are the concern here.

You might have missed what I wrote at the beginning of my first comment. "Assuming you don't have any issues".
What I mentioned is you still have intake valves open and the air would enter to cylinder and goes into crank case, even if PCV valve, valve guides, valve stem seals are fine. If that's the case, nothing is concerned here.
To check blow-by (ring sealing condition), you need to run a leak down test., not by a boost leak test.. So it's not the concern here.

 

[dwb]

Probably fact. FP once explained to me that some turbos seals are "dynamic" in that they seal when the engine is running but will leak air into the engine on a BLT.

What about MHI or Garrett turbos? Pretty sure OP is running a stock T25

You have never heard bubbling sound from oil drain tube while running a BLT by charging the air from the turbo inlet? This is why people tell you to charge the air from inlet of lower intercooler pipe instead of the turbo compressor housing inlet.

No, not once. I typically BLT from the LICP anyway. I'm not disagreeing with you, just not fully wrapping my head around the idea with a stock turbo.
I have a couple MHI turbos on my workbench and I may just have to see what happens when I pressurize the compressor side.

"Assuming you don't have any issues".
What I mentioned is you still have intake valve open and the air would enter to cylinder and goes into crank case, even if PCV valve, valve guides, valve stem seals are fine. If that's the case, nothing is concern here.

So you're saying it's blow-by.

 

[TurboSpider]

Its a small 16 g turbo

 

[DSMPT]

No, not once. I typically BLT from the LICP anyway. I'm not disagreeing with you, just not fully wrapping my head around the idea with a stock turbo.
I have a couple MHI turbos on my workbench and I may just have to see what happens when I pressurize the compressor side.

You can hear the oil bubbling sound if you charge the air from the compressor housing inlet and if you have some remaining oil in the drain tube or/and oil pan. If you hear coolant bubbling sound, that would be a different story.

So you're saying it's blow-by.

No. I am saying that you hear the air coming from valve cover while running a BLT is normal if intake valves are still open.

 

[dwb]

No. I am saying that you hear the air coming from valve cover while running a BLT is normal if intake valves are still open.

Let's backup a minute. OP is pressurizing the intake at the throttlebody. It's a fresh engine so we have to assume that everything in the head is within spec. Let's also assume PCV valve is not leaking. Therefore no air is escaping the intake manifold or head into the crankcase. The next passage is open intake valves and pressurizing at least one cylinder. In a perfect world it stops there and the system holds pressure. But that is not true in this case. Where is the leak into the CC? The only other possibility is the piston rings. As @1990TSIAWDTALON pointed out, this engine likely isn't fully broken in and still needs to seat the rings. So...blow-by.

OP did mention doing a leak down test. So that may offer a little insight. Curious what the leak down is now vs. in 500 miles.

 

[DSMPT]

Where is the leak into the CC?

No offense and sorry if I understood you wrong but it seems you are misunderstanding. It's coming from piston ring gaps. And I am saying that's normal that some amount of air enter to the CC if intake valves were open (The engine temp and how wet in the cylinder would affect it, too). But you can't know if the amount of leakage to the CC is normal or abnormal by a BLT. That's why you need to run a leak down test to know about that.

Have you ever done a leak down test by yourself?

 

[dwb]

No offense and sorry if I understood you wrong but it seems you are misunderstanding. It's coming from piston ring gaps. And I am saying that's normal that some amount of air enter to the CC if intake valves were open (The engine temp and how wet in the cylinder would affect it, too). But you can't know if the amount of leakage to the CC is normal or abnormal by a BLT. That's why you need to run a leak down test to know about that.

Have you ever done a leak down test by yourself?

None taken. That's what we're here for, a discussion so we can all learn. I fully understand the difference between a BLT and a leak down test. I only ever did a leak down test once and it was on a high mileage engine so results were less than desirable.

I wasn't sure we were on the same page but we definitely are with the rings. Maybe "blow-by" isn't the correct term? I never said it was wrong or bad, just the culprit. Isn't that what the OP was looking for?

 

[DSMPT]

None taken. That's what we're here for, a discussion so we can all learn. I fully understand the difference between a BLT and a leak down test. I only ever did a leak down test once and it was on a high mileage engine so results were less than desirable.

I wasn't sure we were on the same page but we definitely are with the rings. Maybe "blow-by" isn't the correct term? I never said it was wrong or bad, just the culprit. Isn't that what the OP was looking for?

No worries, all good
I think the point is you are thinking that the air goes to the CC because of ring sealing issue, and thinking no air (blow-by) would go to the CC after piston rings are seated. That's what I understood, sorry if I am wrong. It may be less but it always has some amount of air go through ring gaps and entering to the CC, and it doesn't matter new or old.

The OP was basically worried because he heard the air from the valve cover and was wondering from where that air came from, correct? (If not, sorry I wan't following this thread well) So I was telling him that if some intake valves were still open when he ran the BLT, he could hear the air from the CC, and it doesn't mean he has cylinder sealing issue for sure. This would even happen on a healthy engine.

 

[TurboSpider]

Whew I am confused . I went from happy to unsure to sad back to happy more times then I can count .

From what I see from the posts above, its normal to have air leak into the combustion chamber doing a boost leak test because one valve is always open and the air goes through the valve into the cylinder and then leaks through the ring gaps, into the CC and comes back up to the head. That makes some sense. I did try rotating the engine to different spots and performing BLT but it all had the same result with air leaking out valve cover vent.

The reason I made this post was one because I was under the impression that the engine should be able to hold pressure when BLT at throttle body elbow. I know I saw some videos where some people did the BLT and it held for a reasonable amount of time. Now maybe they somehow got all valves closed at the same time or maybe removed cams when doing this but I don't remember off hand. Just was under the impression it should hold pressure for a while.

I need to find a way to get a psi gauge on my BLT. Does anyone have an idea how to do this? Actually mount some kind of gauge to it so I have that to go off of and can actually see how long pressure holds before it bleeds off.

Secondly I was doing the BLT test because I was having idle issues/stalling especially when air was turned on which from what my reasearch turned up, you start with a BLT. I was able to get the car to idle a lot better. Turns out my timing was set at TDC instead of the 5BTDC. When I initially set the timing with the engine idling at 750 it kept wanting to stall with the timing pin grounded and engine was surging when I was setting the base timing. I had to bump idle up to 1,000 in order for it to staying running once I grounded the timing pin and once I did this I saw timing was off. Set it at the 1st line BTDC (6bolt timing cover 5 degrees). Also my isc position was hovering around 60 which I was able to get to hover around the 30 mark closer to where it should be by turning biss screw several rotations out. Lastly I bumped the idle RPM up to 900 to account for the BC 272's. It just seems to like to idle around there. I may try lowering it down some maybe 800 or 850 but I have to see how that goes. It has been idling much better since these changes and stays running even when a/c is turned on and engine rpms actually come up when the a/c is turned on which they were not doing before.

So basically I am going to try and get my SD dialed in and drive it around for awhile and increase the break in miles to higher than 60. I will then run a leak down test and post the results here. Thanks for the help everyone.

 

[1990TSIAWDTALON]

If you are running speed density and drive around enough, you can RIGHT CLICK on the log from the drive and select SD Adjust (CombinedFT). Follow the directions but basically you will tell it to "Continue" and it will suggest new values for your SD table derived from your MAP, CombFT and closed loop data. You have to physically change those cells or apply them to your SD table (and always save your log BEFORE you run that adjustment, just in case the car runs worse). It is a nice little gem in the programming that is in ECMlink, in case you were not aware of it.
I did a few screenshots from one of my logs: THE DARK NUMBERS on the SD table are numbers that Link is suggesting that I use in those cells. I would then tell it to apply those changes or manually input them.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

 

[TurboSpider]

Thank you I will give this a shot. So basically if I hit copy all to ecu after it brings up the suggested changes, it will automatically make them for me? Yes I have a few idle logs already saved from after I made the changes to the biss, timing ect so I can use those to revert back if need be.

 

[1990TSIAWDTALON]

Yes. You should drive your car around a variety of terrain like hills, straights, low speed and high speed so the program gets as much data as it can before it suggests changes. The more driving you do, the better the data. Some of the tuners I have used have told me to go drive like I just said and to try and keep the vacuum on the engine (load) the same.

 

[DSMPT]

its normal to have air leak into the combustion chamber doing a boost leak test because one valve is always open and the air goes through the valve into the cylinder and then leaks through the ring gaps, into the CC and comes back up to the head. That makes some sense.

Correct but not one valve, two valves (one cylinder) is correct. And gaps/clearances are open maximally when the engine is cold, so it would let more air pass.
Of course it would depend how much air is coming out from valve cover. I don't know how much air exactly you are talking about but if it's just a little air then you probably have no issue. If all the pressure is escaping to the crank case then probably you have some serious issue. What I have been saying is, in your case you still can't judge if it's normal or abnormal by only hearing the air coming from valve cover while running a BLT if you have intake valves open.

I did try rotating the engine to different spots and performing BLT but it all had the same result with air leaking out valve cover vent.

In case if you can't find the right spot, you can remove the cams, it would make all valves closed for sure and it's less complicated.

I was under the impression that the engine should be able to hold pressure when BLT at throttle body elbow.

Yes it should be able to, assuming you don't have any leak between throttle body/intake manifold and cylinder head.
If it doesn't hold the pressure, then most likely you have intake/exhaust valves open (choosing a wrong spot, middle in overlap) or the EGR valve is stuck open (I would check this first, if you have the stock intake manifold w/ EGR valve. And if this is the case, this may be related to your unstable idle/performance issue) or perhaps you have a issue with valve/cylinder sealing.
In case if the air is escaping from open exhaust valves or EGR port, you should be able to hear the air coming from tail pipe, too. Did you check that?

 

[Buddy2]

Correct but not one valve, two valves (one cylinder) is correct. And gaps/clearances are open maximally when the engine is cold, so it would let more air pass.
Of course it would depend how much air is coming out from valve cover. I don't know how much air exactly you are talking about but if it's just a little air then you probably have no issue. If all the pressure is escaping to the crank case then probably you have some serious issue. What I have been saying is, in your case you still can't judge if it's normal or abnormal by only hearing the air coming from valve cover while running a BLT if you have intake valves open.

In case if you can't find the right spot, you can remove the cams, it would make all valves closed for sure and it's less complicated.

Yes it should be able to, assuming you don't have any leak between throttle body/intake manifold and cylinder head.
If it doesn't hold the pressure, then most likely you have intake/exhaust valves open (choosing a wrong spot, middle in overlap) or the EGR valve is stuck open (I would check this first, if you have the stock intake manifold w/ EGR valve. And if this is the case, this may be related to your unstable idle/performance issue) or perhaps you have a issue with valve/cylinder sealing.
In case if the air is escaping from open exhaust valves or EGR port, you should be able to hear the air coming from tail pipe, too. Did you check that?

Agree. I dont pay much of attention on the air escaping from cylinders to any direction while blt as its not something to find out with it.