STM did a boost leak test before the car went to the dyno. They said it was rock solid minus the tbody seals, which they replaced. The surging is really only in certain loads/throttle positions, only around 2500rpm in 4th or 5th gear while easing off the gas. Another symptom that seems to coincide with the surge is the bov sounds "choppy". The plastic 8 valve, and the 9 valve I just put on both sounded the same.

A bigger issue is that although the car hits peak boost by around 4000rpm, it sounds like literally the gates of hell are being unleashed when I drop the hammer. The turbo has zero shaft play and is smooth, but something is amiss. It is a stock exhaust so it shouldn't be this loud...... and I am really starting to think that the wastegate flapper is not holding shut like it should as the car spools.

I'm trying to troubleshoot this before driving back 2.5 hours to them. They have been quite busy lately.

 

If it all of a sudden became loud, and started to spool slowly. You may want to check the exhaust manifold, could of came loose or cracked. Look for heavy black soot/exhaust building around your head where manifold mates to it, same with black soot building where manifold mates to turbo. Then look for general crack in the manifold.

Have a friend rev it up while your outside the car. Hopefully you'll hear where the leak is coming from.

Also examine the o2 housing.

 

Thanks man, I'm sure it is something that I will find as soon as I can get under the car and give it a good once over. Weather has been horrible around here..........maybe this week.
With the ridiculous swings in temperature around here (-17 at one point last week), I am sure a crack would not be a longshot.

 

If you're just slowly letting off the throttle, the bov might not open while there is still some positive boost.

4000 rpm for full boost seems way to low, I have a Green and big cams and get full boost by 3600 rpm and that is about 32psi.

Get into boost and then just let the throttle go all the way to close, that should open the valve all the way.

 

I can snap the throttle shut and its no issue, its part throttle driveability that is being annoying. Pretty much when I am in fuel conservation mode.

I still think my wastegate flapper has loosened up, it is an original turbo with 100k and I would assume the original actuator spring. That would explain my late spool, and the fact that my turbo sounds like a general electric afterburning turbofan!

 

If I hook up the reference line from the wastegate to an air source how much psi should the actuator hold before it starts opening the wastegate? Like 13-15psi or so?
May test it today.

 

Anybody have a reliable method for testing wastegate operation while it is still on the car?

 

Yes that sounds right.

One way to test is to simply hit the out housing. If you hear metal on metal rattling then you know your flapper is loose.

What you can do is add preload to your stock actuator to try and keep it closed tighter.

 

So upon further review of my dyno sheet, I was hitting 23 psi around 3900 rpm, which I think sounds pretty damn good. I think this all but rules out my wastegate theory.

At this point I am going to conclude that what I am hearing is a bull**** exhaust leak somewhere that isn't costing me boost, but is just making alot of noise. If its not broke don't fix it I guess...............I will keep you guys posted and when I can get the car in the air I think I will have a much better idea of what is going on.

 

Common exhaust leak is from o2 housing to downpipe. The doughnut gasket breaks up. Specially if you reused the OEM doughnut gasket when you changed downpipes.

 

Thanks for the heads up. I am on the stock exhaust, so for all I know there is a hole blown in it somewhere I can't see. I don't smell anything, or see any carbon buildup in the engine bay, but I could have a leak at the downpipe for sure. 60 degrees today, might have time to have a look at it.

 

Idk what is more frustrating, the fact that I know there is something wrong with the car, or the fact that it behaves 95% perfect and just doesn't feel quite right?

Tuned to 23psi perfect, you mash the gas and it rips, not a hint of misfire all the way to redline and it puts you in your seat. You try driving the car any kind of part throttle, and it seems like you threw an anchor out the back of the car and it just doesn't want to rev. Brand new NGK BPR7ES gapped to .028.

I am still thoroughly confused.

Stock cat clogged? Maf? Map sensor? Massive Exhaust leak? Throttle Position Sensor? Coil taking a ****? Where do I even start. I was really hoping they woudl find a massive boost leak, because thats exactly what it feels like.

 

Still no resolution on my sluggish car. Will keep you posted.

 

Update. While driving home tonight with the radio off listening carefully to the car, I noticed something very interesting. In fourth gear right around 10 in/hg on the boost gauge, if you feather the throttle to build a touch of boost pressure I can distinctly hear what sounds exactly like a relay clicking under the hood. The sound seems like it is originating near the turbo, and is repeatable.

My gut feeling is that this is the sound of the wastegate flapper moving off its seat at 10 in/hg, which would very much contribute to my lack of low end grunt. Has anyone ever heard what a sloppy wastegate sounds like to confirm this? Short of this explanation, is there anything else at ALL under the hood that would be making this clicking noise?

 

Well, after talking with the guys at STM I think I have exhausted all of my resources, and it will end up going back to them for more troubleshooting. I asked about the wastegate possibility, but that makes no sense since clearly on the dyno the car hit 22psi by 3800 rpm, and made peak boost very shortly thereafter.

I tried an ecu reset as a last ditch effort to get rid of the sloppy throttle response, but it still feels noticeably off (boggy spool, no misfire but just sluggish). As soon as it crosses over into boost it shoots up. Fuel trims are near perfect, timing is about 30 degrees of spark advance at cruise ( drops to about 7 in the powerband in boost), which sounds about right. Perfect idle. Power to spare in 3rd and 4th gear. I watched the upstream 02 sensor for signs of it hanging up, but switching looked very normal. I feel like I have a closed loop issue but for the life of me can't find it. Very confusing.

I have since learned that the little compressor surge I am getting at times in off power situations is simply a side effect of ditching factory boost control. No biggie. However the lack of bottom end pop is alarming.