I lost 4lbs and don't know why!

[mattw]

Unfortunately I'm talking about boost and not weight. I recently removed and re-installed my fenders so that I could paint them.

While the fenders were off I also added a torque strap to my engine. I have to run these funky offset motor mounts for the V8 and I was afraid that they may bend or deform without something to limit how much the engine can torque. I've since removed the torque strap/limiter to rule out it being the issue..

To troubleshoot this I pressurized the whole cold side and squirted soapy water on all of the fittings to look for a leak. The only place that I found anything is on the turbo itself. My guess is that it's always been this way though and its probably not the issue..

According to the gauge on the regulator I was putting ~11lbs into the turbo:

The boost gauge was only saying 6lbs..

You can see the bubbles where a little air was seeping out of the turbo:

Nothing else bubbled and I checked everything: All plumbing from the turbo to the intake, the inter-cooler, the BOV, the FPR, all the injectors, the intake manifold gaskets..

I also checked the turbo shaft for play and there was none.. The fins aren't damaged and everything seems legit. I made sure all of the bolts on the turbo are tight especially where the little bit of air seeped out.

I also checked and I have no blow-by.. The engine seems fine and it runs fine otherwise..

Here is a before and after datalog.. The boost is the blue line.. You can see its 3-4psi lower across the board..

So I have a couple of questions:

1) Does anyone have any ideas of why I lost 3-4 psi of boost? What else can/should I check?

2) How much air pressure can I put into the turbo and motor? I'm wondering if I just didn't put enough PSI to it to make the problem show.. Maybe something blows open at 8 PSI and I was only putting 6-7 PSI into it?

 

[skolman91]

Re: I lost 4lbs and don't know why!

Since you moved stuff to take the fenders off id double check any boost controller connections/lines, but thats the obvious one and im sure youve checked. With the only difference being a engine strap, for some reason i want to say you should check all the hot pipes pre turbo for a leak, do you have a flex piece in the crossover? Cheap ones have been known to come apart on the inside but that would cause a big restriction and not just a 4psi loss..
Maybe take off whatever youre using for intercooler and check it as well for restrictions..?

 

[gringo76]

Re: I lost 4lbs and don't know why!

if I not mistaken there are times when ecu limits boost to 6 psi for safety reasons, like certain codes so forth. I am sure some wisers will chime in on that. of course that is if you are still using factory boost solenoid . only other thing would be something wrong with wg .

 

[mattw]

Re: I lost 4lbs and don't know why!

Since you moved stuff to take the fenders off id double check any boost controller connections/lines, but thats the obvious one and im sure youve checked. With the only difference being a engine strap, for some reason i want to say you should check all the hot pipes pre turbo for a leak, do you have a flex piece in the crossover? Cheap ones have been known to come apart on the inside but that would cause a big restriction and not just a 4psi loss..
Maybe take off whatever youre using for intercooler and check it as well for restrictions..?

I did physically look the boost controller lines over really good and they got pressure tested along with everything else.. I think they are OK..

I have had leaks in the hot side before and they were always very audible. I'm thinking if I had a hot-side leak I would hear it.. I could be wrong though. Maybe pressure testing that side wouldn't be a bad idea..

I do have flex pipe in the crossover.. It was an expensive one made for turbo applications with no inner liner..

 

[mattw]

Re: I lost 4lbs and don't know why!

if I not mistaken there are times when ecu limits boost to 6 psi for safety reasons, like certain codes so forth. I am sure some wisers will chime in on that. of course that is if you are still using factory boost solenoid . only other thing would be something wrong with wg .

No codes in the ECM and its still commanding the same WGDC..

I thought about taking the wastegate apart and just inspecting things..

I have forgotten to tighten a clamp on the cold side before and had similar issues(only got 4-5 PSI though).. That's why I thought pressure testing the cold side would be a good idea..

 

[skolman91]

Re: I lost 4lbs and don't know why!

Not sure how you would test the hotside, a few valves will always be open or maybe im missing how you would.
Yes a leak is usually loud, but if it only appears when its hot and your in the cab under boost you might miss it for awhile.
Verify Boost gauge and ecm seeing the same pressures? Could keep the wastegate shut and go see if it will make more than 5psi real quick but dont stay in it too long..:lol:

 

[mattw]

Re: I lost 4lbs and don't know why!

I don't think it's a "leak".

Looking at the two logs I see that the Waste Gate Duty Cycle is exactly the same in both. I'm thinking that the DC is a fixed max number, and the ECM allows this max DC, rather than control to a "Target Boost". Ie, the boost is lower at the same DC. The turbo is not as efficient, something has changed (Captain Obvious, here.).

I have manually disabled all correction on boost control. I've set the initial WGDC to 64.84. Its been this way for quite some time and I haven't changed it.

Did you make any changes to the pre-turbo plumbing? Like plumb it to your fender vent or something? A restriction on the inlet side of the turbo will behave this way (lower boost and efficiency) with the DC being the same.

No changes here. Its just a 90 and then the filter..

How is the boost controlled by the ECM? Is it a "target boost" deal like $59 is, or some set value? The identical WG DC really intrigues me. It should lower the DC further to try to get back to the "10.4", but it doesn't.

As mentioned above I disabled correction on the boost control.. I found it to be pretty stable just holding the WGDC static so I never bothered to re-enable any sort of correction.

What about knock and timing? Pulling timing with a fixed WG DC will result in lower boost.

No knock on either run. I just looked at the logs again and the spark advance was the same on both.. Right around 25.

This engine must have a tiny cam in it. There is always at least one intake valve open to some extent at any point in the crankshaft rotation. To get 5psi manifold pressure with 11psi input is remarkable. The intake valve isn't open very far at all.

I was wondering about that too... Its just a stock LT1 cam with 1.6" roller rockers. I think its the 2nd one down on this list:

I couldn't recall if there was a point where all intake valves were closed or not.. I found it a bit odd that I was able to pressurize everything like that. Would it run fine otherwise if something were off in the valvetrain like that? I'll repeat the test and see if I can still build pressure in the intake like that.

0-82 in 6 seconds? Is that KMH rather than MPH,? If indeed MPH, that is a fast-azz truck at 10psi. Coolness. :tup:

That is MPH and it did feel very fast at 10-11 PSI.. I was quite happy with how things were going and intended to bump my boost PSI up a pound or two then this happened..

I have another thought. Has to do with the 5psi of manifold pressure, which shouldn't be possible:

IIRC, awhile back you pulled an intake rocker stud out of the head. Or enough to make a difference. If you've done this again, that could explain the manifold pressure, because the effective duration on any valves so affected would be much less than if the geometry was correct.

If you can't find the smoking gun, pull the valve covers and take a look.

You shouldn't be able to pressurize the intake manifold with an outside source. The only way it will be possible is if something is wrong with the valve gear.

You are correct.. I did pull a stud on these heads some time ago.. I now have screw-in-studs.. You have me wondering if I have something off in the valvetrain. I had the short block assembled but I installed the heads, pushrods, rockers, etc.. I'm wondering if I've had something wrong all along.. Still doesn't explain the sudden loss of 4 psi though..

 

[RealFastV6]

How "sudden" was this change?

One of the issues with running open loop boost control based purely on WGDC is that your boost becomes dependent on atmospheric conditions.


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[mattw]

Re: I lost 4lbs and don't know why!

How "sudden" was this change?

One of the issues with running open loop boost control based purely on WGDC is that your boost becomes dependent on atmospheric conditions.


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The truck sat for about 3 weeks while I body-worked and painted the fenders..

I noticed the difference immediately though.. At 10-11 PSI I'm afraid to take my eyes off the road to look at the speedo.. The first time I took it out after re-installing the fenders I was looking at the speedo thinking this isn't right I must have a loose clamp somewhere on the cold side.. That's when I started digging into it and couldn't find anything..

IIRC weather conditions haven't changed much here over those 3 weeks..

 

[Don W.]

Re: I lost 4lbs and don't know why!

Assuming the exhaust side is tight you could cap the tail pipe and run the pressure to whatever you want. This should make it a "closed system." The one thing that always comes to mind for me on these issues is a blown intake gasket -into- the valley. You'll never find it with soap. You might hear it at the oil filler. This could explain a lot.

:2cents: If an intake opens every 120* and stays open for more than 180* there will always be at least one open somewhere. No?? The trick would be to not be in overlap. Otherwise you're gonna just fill the cylinder(s) I'm not fully awake yet so the above may be wacky. :rotf:

 

[dgoodhue]

Re: I lost 4lbs and don't know why!

The one thing that always comes to mind for me on these issues is a blown intake gasket -into- the valley. You'll never find it with soap. You might hear it at the oil filler.

You may notice a blown intake to engine block by looking a vacuum gauge at idle. I had one in my Corvette and the vacuum gauge was reading higher than expected but it also jumped around from 14-18" hg at idle.

 

[Don W.]

Re: I lost 4lbs and don't know why!

0-82 in 6 seconds? Is that KMH rather than MPH,? If indeed MPH, that is a fast-azz truck at 10psi. Coolness. :tup:

Thanks for our comments Dave.

My truck (12.3 in 1/4) will do 0-83 in 6 secs per DM. Don't know how accurate that is. Traps @ 107. Boost starts at 16 then goes to 18 on the 2-3 shift. I'm leaving on 6-7#. Just for comparison, that is a quick ruck. Makes for a zippy ride!

And, yes I wasn't awake yet. I was taking 6 cyl, not 8.:rotf:

 

[dgoodhue]

Re: I lost 4lbs and don't know why!

I would be half tempted to increase your boost by a small amount and see how it responds to that. My thought are thinking maybe something is not working properly with the wastegate. DonW is probably on a more likely track.

 

[Don W.]

Re: I lost 4lbs and don't know why!

I wouldn't doubt that at all.

 

[mattw]

Re: I lost 4lbs and don't know why!

You may notice a blown intake to engine block by looking a vacuum gauge at idle. I had one in my Corvette and the vacuum gauge was reading higher than expected but it also jumped around from 14-18" hg at idle.

My vacuum at idle is 20Hg.. That's what it has always been and thats what it still is.. It doesn't jump around at all. Sits perfectly still.

I would be half tempted to increase your boost by a small amount and see how it responds to that. My thought are thinking maybe something is not working properly with the wastegate. DonW is probably on a more likely track.

I thought about that too.. I just want to be 100% sure I'm not overlooking a more serious issue before I give that a shot..

Matt's 4-door probably weighs 800 pounds more than a Syclone, and the 0-83 times are the same. The power to weight ratios are the same, so the V8 appears to have more output @10psi than the V-6 does @15psi.

That wouldn't surprise me.. Its a 383 stroker with all forged internals and recently new build. Coated Mahle Pistons with a 9.1:1 compression ratio.. Vortec heads with nearly .5" of lift on intake and exhaust.. There are lots of reasons that it should make good power..


So.... I had some time over lunch to do more testing today..

To start I put the Mity-Vac on the vacuum lines that go from the boost controller to the wastegate/turbo... everything checked out fine without any leaks. Next I capped the charge pipe just after the turbo then pressurized it right where it enters the engine. I put 20 psi in it and nothing leaked. That proves out the plumbing, intercooler, and the BOV..

Then I decided to verify that the engine will not flow air through it.. I pressurized the engine right at the throttle body and put 12psi to it.. No leaks and it absolutely does not let any air through. I went back to the exhaust pipe and couldn't hear/feel any air coming out..

When I first put this truck together I had a stock TBI short block with my vortec heads on it.. I had some exhaust leaks and I pressurized the exhaust to find them.. IIRC that engine wouldn't allow any air to flow through it either. Once I fixed all of the exhaust leaks I could pressurize the exhaust and it would hold the pressure..

 

[mattw]

Re: I lost 4lbs and don't know why!

How "sudden" was this change?

One of the issues with running open loop boost control based purely on WGDC is that your boost becomes dependent on atmospheric conditions.
.

I would be half tempted to increase your boost by a small amount and see how it responds to that. My thought are thinking maybe something is not working properly with the wastegate. DonW is probably on a more likely track.

Maybe you guys were right... I increased the WGDC to 75 and that brought me back up to 10 psi.. It feels like an animal again..

I'll have to start playing with the desired boost values as well as the WGDC step correction values to see how well I can get Code59 to hold the boost I want...