Boost leaks...

[IHI-RHC7]

So Heidi and I built the $5 boost leak tester (it ended up costing closer to $8 since we used high quality neoprene hose, instead of rubber) and we found a HUGE leak...
The throttle body port to the cam covers for the PCV system was leaking so bad we couldn't build any positive pressure.
After capping off the port on the throttle body, we found that the flange for the SSQV is also leaking a tad, but not nearly as bad as the throttle body was.
So while I dinked around with the BOV, Heidi swapped out the TB for a spare one we had lying around.
The problem is that the new one seems to blow straight through as well. It was my understanding that there was a check valve inside that port that allowed the intake manifold to apply vaccum to the crankcase, but would not allow manifold pressure to flow the other way.
Testing both throttle bodies, it seems that there is no check valve in either, or both check valves are shot. Assuming that there is no check valve, how on earth is it supposed to work? It is a straight shot from intake manifold pressure to the accordian pipe. The TSRM says nothing about a check valve, and only mentions that you should clean the orifices with solvent, and blow them out with compressed air. I suppose it is possible that both TBs are shot. Can anyone verify if there is a check valve, and if so, is it strictly a one-way valve, or does it require 5 psi or so before it closes?
Any help with this would be greatly appreciated.
Thanks,
-Jake

 

[IJ.]

Makes sense to me that it would need a check valve in there Jake!
(Never owned a GTE so no real idea if it has one or not)

 

[IHI-RHC7]

Well, that's what I thought. I'm hoping I'll hear from someone that there is, in fact, a check valve in there... That would explain the fall off of boost past 4500 rpm and the screaming that the turbo makes when boosting...
(trust me, I know ct26s, and it IS NOT the death whine. There is no shaft play, it just hoots like you popped an IC hose when boosting in first gear...)

 

[IJ.]

Well if there's no nonreturn or check valve you'd be blowing boost pressure into the crankcase. (just looked at the TRSM and it's as clear as mud)

 

[GrimJack]

I could go outside and check this... but how the hell would I go about it? Pull off the rubber hose from the throttle body and try to suck from the throttle body port?

 

[IJ.]

GrimJack Sucks <jk>

 

[IHI-RHC7]

Grim, That's exactly what I did...
Well, I used the tester to do it for me
Have you used the tester you preach about so much?
If you have, did you test with the throttle plate open, or closed?

 

[Afunk]

the port on the throttle body for the PCV system has no check vavle...under vacuum it sucks oil vapors into hte intake tract, and under boost, it blows pre-turbo which helps the rings...basically, cap that port off or use it for it's stock function...

 

[GrimJack]

No, my boost leaks were... err... obvious. When you have a hose that's cracked for 6 inches along it's length, it's pretty tough to miss.

Since then, I've replaced literally every hose but one in the engine bay... my lower rad hose is still stock.

 

[gixxer750]

funny thing grim, my lower rad hose was too until about a month ago....those things hold up quite well

 

[IHI-RHC7]

the port on the throttle body for the PCV system has no check vavle...under vacuum it sucks oil vapors into hte intake tract, and under boost, it blows pre-turbo which helps the rings...basically, cap that port off or use it for it's stock function...

What could the "stock function" of blowing boost into the accordian pipe possibly be?
We're going to cap it off reguardless. It really makes no sense that toyota would have engineered a massive boost leak into our cars, and if they did, why has nobody figured out, until now, that the port on the throttle body is toyota's second worst engineering ploy yet?
We're going to get a better pump today and pump the pipes up to 20 psi, and see what happens with lots of pressure.
If there is no check valve, It would be a MAJOR upgrade for everyone to block that port.
As Ian said above, not only would it pressurize the accordian pipe, but it would effectively pressurize the crankcase, which was a bad thing, last time I checked...

 

[jetjock]

There is no check valve in the TB port. One could be added but calibrated orifices are often used in place of them, especially in PCV systems. The GTE isn't unique in this regard. The bottom line is there can never be enough flow thru the orifice to pressurize anything as long as the crankcase is connected to the accordian hose or vented to the outside.

Think of the volume of the cranckcase and plumbing. Now think about trying to pressurize this large volume thru an orifice by using a small delta P like 20 psi for the short time it's there. Not to mention the negative pressure in the accordion hose, even under boost. This increases the delta P even more.
In short, you're failing to consider the differences in pressure/flow between a static system (engine off) when using the leak tester and when the engine is running.

There are other reasons for plugging the TB PCV port but solving a boost leak isn't one of them and a major upgrade it wouldn't be. Yes, it's true you'll remove a tiny leak but it'll gain you nothing in boost. What it will do is route all your blowby to the turbo. Better use a good separator if you're going to do that.

Btw, an often overlooked cause of legitimate boost leakage is a bad ISC check valve. Most people forget it's even there. A failed one will not show up on a leak test unless the intake plenum is pressurized.

 

[IJ.]

JJ: Damn good post and thanks for the explanation!
(Always said this is a huge strength here at SM people willing to impart knowledge, learning all the time here)

 

[jetjock]

Thanks Mate. In return I'd like to say that after persuing this forum in depth I find you to be hands down one of the most knowledgable here. I'm able to make that judgment accurately not because I don't know my shit but precisely because I do. The devil is in the details and it's obvious you take learning very seriously. Such an atttitude will continue to serve you well.

 

[IJ.]

JJ: You've made me blush!

Thanks I'm a bit of a sponge and love learning new things and usually don't post an opinion until I've researched it or have some experience in the past.
(been wrong a few times and am always happy to admit it learn from it and move on)

No one knows everything the 1st step is in understanding this then asking for help .

 

[chriso]

Jake and Heidi,
Can you post a pic of the cheapo boost leak detector you made up and what ports did you plug off to test.
Thanks in advance....
BTW, good informative thread.

 

[IHI-RHC7]

There is no check valve in the TB port. One could be added but calibrated orifices are often used in place of them, especially in PCV systems. The GTE isn't unique in this regard. The bottom line is there can never be enough flow thru the orifice to pressurize anything as long as the crankcase is connected to the accordian hose or vented to the outside.

Thanks, I gather that pressurising the crankcase is not going to happen, but if you remove the throttle body and look at the port, it is not exactly a calibrated orifice per se. It's a 1/4 inch hole. The vaccum cap size that covers the port is 9/16. I'm familiar with metered orifices, most pcv valves have some restriction, keeping them from being a vaccum leak. I can't feel any restriction when I blow through it, and I don't see how it wouldn't be a leak.

Think of the volume of the cranckcase and plumbing. Now think about trying to pressurize this large volume thru an orifice by using a small delta P like 20 psi for the short time it's there. Not to mention the negative pressure in the accordion hose, even under boost. This increases the delta P even more.
In short, you're failing to consider the differences in pressure/flow between a static system (engine off) when using the leak tester and when the engine is running.

Agreed. My primary concern was the robbing of boost. However, I do think that it would make sense that in the process of opening one side of a pipe to pressure, and the other to vaccum, it wouldn't aid in venting the crankcase.

There are other reasons for plugging the TB PCV port but solving a boost leak isn't one of them and a major upgrade it wouldn't be. Yes, it's true you'll remove a tiny leak but it'll gain you nothing in boost. What it will do is route all your blowby to the turbo. Better use a good separator if you're going to do that.

With the throttle body port capped, the car now hits 17 psi at 5,000 rpm, where it only had 10-12 psi max before...
I understand the legitimacy of your post, but I think it actually is a big deal.
Also after capping the port, it took the ecu 30 minutes of driving, and I had to flash the ecu to make it idle above 450 rpm. The engine was used to breathing through that hole. And the turbo was used to losing all of its breath passed 4500 rpm through that hole.
To put it into perspective, go drill a 1/4 inch hole in one of your hardpipes, and tell me you can't feel the difference, or see it on your boost gauge when you're pushing your turbo to the limit.
We'll adress the blowby issue with a proper catch can/seperator in the near future.

Btw, an often overlooked cause of legitimate boost leakage is a bad ISC check valve. Most people forget it's even there. A failed one will not show up on a leak test unless the intake plenum is pressurized.

The plenum was pressurized. The throttle body port is also behind the throttle plate, so many people are unaware of its tendancies. The ISC check valve is in good shape, and after capping the throttle body boost response is much better. Also, the Kf is lower all around the board now. So I refuse to believe that everything is fine with the way toyota set things up from the factory. Maybe with 6psi, but when your running 17-18 psi boost leaks are no little concern.
Thanks for your informative reply jetjock, But I do believe that what I did was "fixing" a problem.

Jake and Heidi,
Can you post a pic of the cheapo boost leak detector you made up and what ports did you plug off to test.
Thanks in advance....
BTW, good informative thread.

We'll compile the pics and post them tomorrow chriso.

-Jake and Heidi

 

[jetjock]

Hi IHI,

It wasn't my intention to rain or your parade. It's just some things didn't add up.

1) 1/4 inch hole? Very strange. On my car it's a tiny orifice. The hose connection is larger (still not 1/4 inch) but the actual orifice located in the throttle body throat is very small. I'd guess around .020"-.030" from looking at it. What year is your car?

2) Opening one end of the PCV pipe to pressure and the other to vacuum would indeed scavenge the crankcase as the flow thru the pipe would be increased. This would increase the venturi effect across the valve cover ports. Think blowing across the top of a bottle.

3) You're certainly correct in that capping the PCV port removes unmetered air issues. This is one benefit of doing it, along with not drawing blowby into directly into the TB. I'm not saying it's a bad thing to do, I'm saying it shouldn't effect boost. Course, I'm talking about the stock metering, which it seems you don't have. I was formulating my response based on the much smaller orifice. Why you have such large PCV metering is a mystery..

4) By "flashing" the ECU did you mean a reset? The ISC system has more than enough conductance to compensate for PCV air and then some, even if it's open to ambient. Just look at the ISC valve and piping volume compared to the area of even a 1/4 hole. Reseting the TCCS won't change anything relating to ISC. All it would do is cause the ISC valve to end up at a different position at ilde, something it would have done without the ECU needing a reset. The idle speed code is not adaptive, there is no "learning" applied to it.
It's "stupid" in that it's a nothing more than a fixed code feedback loop with selective setpoints. However, a leak that size would effect idle because of mixture issues and the TCCS would adapt in that regard, so I can see how restting it could cause the changes you saw.

If capping the port worked than great. However, I still can't see how leakage thru the PCV system was the root cause of your problem unless the PCV port is huge. Even then I'm puzzled. Boost leaks tend to be, generally speaking, overhyped. For example, how many people have unknowingly driven around with the failed stock blow off valve? You won't see that at stock levels and it's difficult to feel unless you know what to look for.

I'm curious, what is your Kf at hot idle now?

Btw, since I have a smoke machine I've never had the need to check for leaks using plain compressed air. Smoke is so much eaiser.

Lastly, me thinks you're underestimating the OEM engineers more than a little. They're not incompetent, far from it. This seems to be a common attitude among modders and one I've never understood. If the engine is modded beyond the original design one can hardly blame the factory engineers if something needs to be tweaked.

 

[IHI-RHC7]

Agreed Jetjock, That's why I said it probably works great with stock boost levels.
Admittantly, we're squeezing the last little bit of capability out of the stock turbo, so things are kind of "on the wire" so to speak.

The 7m is one overwhelimingly overengineered engine. With that said, I believe the engineers did a great job on almost every aspect of the engine. However we have proved that they are not foolproof.

1. Factory head torque. We all know that someone wasn't thinking clearly when they torqued a turbocharged straight six to 58 ft-lbs.

2. Factory oil cooler. We all know that it is a joke, It cools oil based on pressure, not temperature. I suppose the idea says "if your pressure is high, your reving the engine, and the oil needs cooling" fine. Why then did they dump it into a sump of hot oil? Poor engineering, no other way.

3. Both throttle bodies I used have no smaller than .25" holes on the back of the throttle plate. one tb is an 89, the other is an 87. Both have the same sized holes. I'll take a picture when I get home.
Engineers are far from incompetent. But they do err. Why else is there a 2jz? if they did everything correct on the 7m, there would be no need for replacement. The 2J is better. intake tract? Better, Valve spacing? Better.
I'll bet that their pcv system is better too.
Anyway, I won't blame the engineers for not thinking about boosting further than stock, I will, however, say that capping it off fixed several problems. The hoot is gone, as well as the lack of boost.

On to pics Note, this pump is WAY too small to build any pressure, but it looks good in the pics.

Finished product. The PVC cap is for a 2" pvc conduit, OD is 2.75"
It was $2.70 @ home depot. The clamps were old TB to 3000 pipe clamps.
The neoprene was $2.30 per inch @ knechts! 2" worked great.
The valve stem was $1.50, also @ knechts. Grand total, $8.80.
I'd recommend a large volume bicycle pump to presurize the system.
The drill bit I used was a 15/32. and I used the tube on the pump to
pull the valve stem through. The hole you drill depends on the size of
valve stem. I got the .493" I believe.

Testing procedure:

Well, that pretty much sums it up.
Here's some shots of the port I plugged,
in case you want to contaminate your turbo
and and not benefit from not fixing a boost leak.

 

[IJ.]

So Michael got all the looks ? <jk>