It's not often I come here with a serious puzzle, but...

alfadriver wrote: In reply to Fueled by Caffeine: Come back http://corporate.ford.com/careers.html?gnav=footer-aboutford

Don't tempt me. A straight salary job from here to Detroit would be big lifestyle increase. I got an old mentor who is a VP at GM.

Fueled by Caffeine wrote:

alfadriver wrote: In reply to Fueled by Caffeine: Come back http://corporate.ford.com/careers.html?gnav=footer-aboutford

Don't tempt me. A straight salary job from here to Detroit would be big lifestyle increase. I got an old mentor who is a VP at GM.

If that's the case- http://careers.gm.com/#.html

kb58 wrote: About this "awesome thread"... I see it as "be the change you want to see." I greatly enjoy open discussions that figure out problems. Not only is the person presenting the issue helped out, but everyone walks away smarter. Best of all are threads that have the solution at the end, not the typical threads that just die out, leaving everyone wondering what happened. On some of the other forums I'm on, they're dying off because no one bothers to spell things out. Worst of all are threads like "My car runs like crap, why?", then they get pissed when no one answers, and they never post what the problem was. Just my contribution... sort of like peeing into the Grand Canyon sometimes, but if we all do it... okay, bad analogy, carry on! I'll change the wastegate spring because I'm pretty sure that he's right. Oh, and lastly, I built up a turbo car in order to learn all about them, and boy, have I. What keeps amazing me is just how much more involved the system becomes with the addition of just one simple spinning part!

Ha.. My first post was skeptical of Wastegate... :-) Maybe I ain't as dumb as my current employer makes me think I am..

alfadriver wrote:

Fueled by Caffeine wrote:

alfadriver wrote: In reply to Fueled by Caffeine: Come back http://corporate.ford.com/careers.html?gnav=footer-aboutford

Don't tempt me. A straight salary job from here to Detroit would be big lifestyle increase. I got an old mentor who is a VP at GM.

If that's the case- http://careers.gm.com/#.html

You are a horrible enabler.

In reply to Fueled by Caffeine:

My pleasure.

alfadriver wrote: In reply to Fueled by Caffeine: My pleasure.

I hate to say it but my wife would like detroit better. Closer to her family. but not leaving until next summer.

Detroit sounds, cold.

That being said, these silly vw's I deal with have an issue pushing the wg open. I have never seen it happen that fast and they use an even lighter base pressure.

I wonder now if this is the real reason why my Volvo drops boost. Certainly Subarus use a similar turbo (13t vs. my 12t) and they have no problem making 18psi with it, with a more restrictive exhaust setup.

Booooo! Swapped in a 200 kpa spring and it still does it just like before. Sigh... Guess school isn't done with me just yet.

Laugh. With one eye twitching.

Dang, I was really hoping I'd won the free book with my waste-gate hypothesis.

Next guess: pressure wave harmonics in the intake or exhaust system. I don't suppose you can log turbo rpm can you? It would be interesting to see if it's speeding up (issue with the cold side) or slows down (issue with the hot side).

Is there any change in sound from the turbo when you hit 7500 rpm? Less intake noise (turbo spinning slower, making less boost or spinning quicker, losing it upstream.)

In my experience, timing, fuel, or ignition issues don't cut boost. The boost is still there, the power just doesn't match what the boost gauge would indicate. It would have to be a big problem to affect boost, and the lack of boost would probably be the least of your worries at that point.

I'm still thinking it could be something to do with the valve train. Are the valve springs stock? 7500rpm isn't high at all for that motor, but boost pressure can cause the valves to float at a lower rpm. Maybe a weak valve spring is acting like a blow off valve?

My next out there question was whether the air inlet for the airbox was drawing from an area that became a low pressure zone as the car's speed increased. The thought being that by the time you hit the upper RPM in third gear it sounds like might be closing in triple digits. Maybe some combination of the cars aero and the airbox design was causing a stall.

Now that I write it out doesn't seem likely.

kb58 wrote: I don't know whether to laugh or cry. Swapped in a 200 kpa spring and... it still does it, just like before. Sigh... Guess school isn't done with me yet.

So is:

Boost cut out at 7500rpm

is not (either from tests or data driven)
ECU
wastegate
spark
fuel
pressure related (happens at different pressure- always at 7500rpm) pressure related (does not happen at same pressures below 7500rpm)

What am I missing on that list?

For argument's sake, can you run a test with the bypass valves mechanically eliminated? Pinch off the hoses. So that we can eliminate that from the list, too.

Is the PCV system resonating so that the back flow valves are opening? Again, an easy test would be to block off for a test. The harm for a quick test for no PCV isn't an issue.

What else?

I'll try disabling the blowoff valve. However, as was pointed out, if there as a sizable leak on the intake size, the turbo would overspeed trying to make up for the drop in pressure - I don't know, maybe it is, but I don't hear anything strange when it happens.

I'll also run a hose straight from upstream of the throttle to the wastegate, completely removing the boost control valve from the system both electrically and mechanically.

PCV doesn't exist, it's running a dry sump.

I wonder if there's a way to log cam angle... not what they're being commanded to, what they actually are. I wonder if it's doing some cam switching or shifting, but without actual feedback, seeing only the command side doesn't help... much.

I have to start reexamining everything that I think is working correctly, because something isn't. I remember arguing with my brother about things like this. He'd have something that wasn't working, and I'd give a list of things to check - he'd shoot down every suggestion, saying it obviously wasn't the cause. When he finally stopped talking, I used a quote given to me one time, "No one knows anything, the results speak for itself." So yeah, this is very humbling, as clearly something I think is fine, isn't.

It may help to draw a diagram of the entire air flow path. Just block diagrams.

That way you can check off things you eliminate as an issue.

So the engine has VCT? Without feedback, how are you controlling it? I don't suspect that too much, as it would manifest itself in how the fuel and spark would run- especially the fuel.

You are running a WB set up, right? Do you have the feed forward value of the fuel? You can see that the feedback control is good- since it's maintaining a good mixture, but the feed forward part may show some other indicator.

Boost_Crazy wrote: Is there any change in sound from the turbo when you hit 7500 rpm? Less intake noise (turbo spinning slower, making less boost or spinning quicker, losing it upstream.) In my experience, timing, fuel, or ignition issues don't cut boost. The boost is still there, the power just doesn't match what the boost gauge would indicate. It would have to be a big problem to affect boost, and the lack of boost would probably be the least of your worries at that point. I'm still thinking it could be something to do with the valve train. Are the valve springs stock? 7500rpm isn't high at all for that motor, but boost pressure can cause the valves to float at a lower rpm. Maybe a weak valve spring is acting like a blow off valve?

There's so much noise from everything (mostly wind, but also road noise, intake, exhaust, and the engine itself) that I wear earplugs by default. So no, I don't hear anything obvious, but that doesn't mean there isn't something going on.

If valve float was going on, I'd expect rpm to drop off significantly, but it doesn't. The engine was built to handle 9300 rpm and because it happens at any boost pressure, something else is going on.

Valves floating due to boost... seems unlikely because boost didn't affect them earlier.

In reply to kb58:

Or to make sure it's not flopping around, wire it open. that would be a very interesting test.

IS there a boost cut/soft revlimiter in the ECU at 7500?

No, checked and varified by me and the ECU techs. Redline fuel kill is at 8000.

kb58 wrote: No, checked and varified by me and the ECU techs. Redline fuel kill is at 8000.

Does the car kill spark or fuel at 8krpm? Maybe try raising the limiter a bit... just a thought. I seriously doubt that is the case though.

EGR related?????

No EGR system.

HiTempguy wrote:

kb58 wrote: No, checked and varified by me and the ECU techs. Redline fuel kill is at 8000.

Does the car kill spark or fuel at 8krpm? Maybe try raising the limiter a bit... just a thought. I seriously doubt that is the case though.

Either one or both but I have it killing fuel only.

kb58 wrote: No EGR system.

You sure did come here with an interesting puzzle.