Well, nice that you found something wrong. I agree with Jeff NJ, order a Tial, but you will need to cap the tube to your muffler. Pretty sure the nuts holding that on are copper, if not they should be, Older BMW copper exhaust nuts will possibly fit.

Okay fellas,

I finally received the Wastegate Diaphragm, installed it and buttoned everything up. I dialed back the output on my air compressor to 11 psi/.5bar. I do hear air slipping past the valve guide (guessing here) if I barely push air through. However, the valve does open and snap closed when pressure is applied at once vs. gradually. (not sure if this is problematic or not)

Presumably, when the wastegate is operating correctly, some air will slip by between the valve stem and guide (maybe not, don't know), but if the volume of air increases to the point that it exceeds the rate of loss between the valve guide and stem the valve will open preventing over boost.


Still no boost, and I'm definitely not leaking any boost. I replaced all the big orange o-rings and put a very light coat of Permatex grey form-a-gasket just for extra insurance. This stuff easily and cleanly can be removed and I was just trying to be sure I wasn't leaking anywhere.

So I shifted my attention back to the WUR and stumbled upon Alan's thread.

https://forums.pelicanparts.com/911-930-turbo-super-charging-forum/602443-wur-tuning-mod.html

I started wondering if I didn't have the WUR set up quite right after rebuilding it as it's been awhile.

I rechecked my system pressure and warm and control pressures.
My system pressure is 6 bar and some change (don't remember exactly)
My warm pressure without boost is 3.6
Cold pressure is fine (given that it's 100F here) it's hardly "cold"
My pressure with boost (simulated with manual pressure pump at .5bar is 2.8 and returns to 3.6 after pressure is released. So as far as I can tell the WUR is functioning correctly.

Something I didn't think to mention before but may have some impact but who knows. Is the Air Pump belt was missing and the air pump was frozen so I removed the air pump (11), blow-off switching valve (12), control valve (13) and check valve(14) and plugged the hole where the control valve connected in the in the Air bypass housing with a bolt. The numbers associated with these components comes from the Euro Hose connection plan in the 911 Turbo Workshop Manual.

The air injector in each cylinder and their respective hardlines are still installed as I didn't want to risk breaking them off. The check valve was removed (as stated above) and the end of metal hardline where the check valve was installed is open to atmosphere (not sure if this is a problem) this just occurred to me... I mean I guess it's possible that I'm leaking enough exhaust gas pressure through the open end of the air injection assembly that it's a parasitic draw on the turbo and limiting some of the exhaust gas pressure making it's way to the turbo.

The control piston that is "normally closed" but opens when exposed to full manifold vacuum directing the compressed air from the turbo back to the turbo inlet is closed at rest so my assumption would be that if it wasn't working properly it would be stuck in the open position and fighting the spring pressure in the valve housing and just recycling the air pressure back to the turbo in a continuous loop. (I verified with a borescope that it is closed and not stuck open without any vacuum pressure).

Care to join me in my sleepless nights over this thing? I am at a loss.

Only thing I can think of is there is some problem with the turbo. (it freely spins by hand) so I think it's safe to assume that if the engine is running then it's spinning. Now how fast its spinning and if there is pressurized air leaking possibly due excessive end play at turbo shaft???.... well I hadn't checked that. I'd think that it would at least generate some boost.... but nothing.


The car seems to run fine, just no boost. Doesn't seem to have a vacuum leak, I mean I have been through that multiple times with a smoke machine. If the wastegate had failed it would be more likely cause over-boost vs. no boost as it would need to be stuck open like the recirculating valve.

I can't generate enough vacuum pressure quickly enough to move the piston in the recirculating valve back with my manual vacuum pump, but again, it's not stuck open.

I'm literally going crazy with this thing!

i had issues with my oem wastegate as well, i changed diaphram inside but i was also hearing air-hiss using compressor.
I called up Brian and got me Tial and short dump pipe and all is good now.
But my symptoms were not as yours with no boost.
I can only think of leak somewhere.

I hear you. I was trying to keep things original and thought I'd just replace the diaphragm. I put some sealant on the open end of the hard tubing along with a rubber cap. I need to run to the store and get a clamp to properly secure it before I can report back if this fixed the problem. Stay tuned! Bill

I kinda doubt that that open end of the air injection plumbing would be a large enough parasitic draw on exhaust volume to affect the turbo. Who knows, I could be wrong.
I just recently cut off the belt to my air pump because it was making noise...either the pump or I had the belt adjusted too tight but I really didn't care which. I left all the associated plumbing in place.
Side note, some air leaking past the WG valve guide and stem is normal, unless it's way excessive.

Thanks Mark, we shall see! Man it should would be great if it was as simple as blocking the open plumbing off.

by the way, for the life of me i could not properly test the oem wastegate with my compressor.
Let us know your next point of test.

i went same route as keeping everything OEM but i gave up...i still have all my oem parts ready to go

Well no luck, no boost. Could it be a fueling issue? I mean as I accelerate and the RPMs begin to climb it just seems to fall flat above 3k. Like if I kept my foot on the gas it would probably wouldn't accelerate. It's not like it falls flat on it's face it just seems flat.. don't know how else to describe it.

I mean if my pressures are good I'd think it would be running fine. Only thing I can think of is fuel volume. Maybe it's passing the control and system pressure tests but when it really needs large quantities of fuel the pumps are lacking. I did check the fuel output a year or so ago but that was prior to me replacing the fuel accumulator. Additionally, I purchased 6 baby bottles and pushed the injectors through the nipples, the variance per cylinder was negligible and volumes per cylinder were within spec. I did this after rebuilding the WUR and Fuel Distributor.

This is kind of a new piece of info. Has that always been the case where you are flat on power beyond 3000 rpms?
When it falls flat like that, look in your rear view mirror. If you see black clouds of smoke behind you, that would mean super rich. Same thing can and will happen with a serious air leak; some of the previously metered air escapes. You just lose all power and she bogs down and runs like dog poo. Been there once when one of my IC o'rings gave up the ghost. Car would run fine until boost pressure dislodged the o'ring, leaving me with the hp of a VW Bug.

Mark,

Yes this is new info as I have been hesitant or unable to drive it due to waiting on parts. Historically though this has not been an issue.

Okay so here are some links from my drive a few minutes ago. I wouldn't say if falls flat on it's face but it definitely seems underpowered.... and no black smoke.

The videos were all under smooth acceleration ending with the pedal on the floor. It's not like it won't continue to climb in RPM through the range.



https://youtube.com/shorts/1-aukrUHU3g


https://youtube.com/shorts/aDdIydrYYUU

https://youtube.com/shorts/228513M0P3Y

Weird. If that's pedal to the metal, even without any boost it should respond better than that I would think. Your revs are so slow to climb though your idle sounds good.
Have you checked your ignition timing, particularly at 4000 rpms to make sure you've got sufficient advance around 26° - 28° BTDC?

I see no reference to air fuel ratio, do you not have a gauge?
Maybe I'm the king of overkill but I have air/fuel and control pressure gauges in the dash. Comparing a/f and control pressure while driving always seemed to be the best way to keep an eye on these old cis cars.
Good Luck!

Mark and Steve, I’ll recheck my timing and I have ordered an AFR gauge. I’ll report back on timing today and the AFR after I’ve got it installed.

Thanks guys,

Bill

I'm guilty, or lazy. Used to have an Innovate AFR guage in my first 930 but just haven't got around to getting another.
Control pressure gauge in the dash would be real convenient. Did you have to plumb fuel lines up to the dash, or using some sort of electronic pressure sensor back at the WUR and wired to a gauge up front?

If everything you say checks out has actually checked out, the turbo becomes suspect. Sort of like the Sherlock Holmes saying about whatever remains, however improbable, must be the truth…
Turbo shafts can seize and break and you could still spin one side with your finger.

But also get a wideband gauge already. I think we’ve told you that before. They are mandatory for diagnosing but also for protecting these now stupidly expensive engines.

Hey Bill,

Sounds like you’ve already done a ton of solid diagnostic work—kudos for being so thorough. A few thoughts and suggestions that might help pinpoint the issue:
1. Boost Control Line Whistling: You mentioned the control line to the wastegate “whistles” when removed. That suggests a strong vacuum source, but it’s worth double-checking whether that line is properly connected to a boost signal under load. If the wastegate is being fed vacuum instead of pressure, it might open too early or not close at all under boost, preventing spool-up.
2. Wastegate Function: Have you confirmed that the wastegate is actually closing under load? A stuck-open wastegate (even partially) would result in zero boost while still letting the engine rev cleanly. Try pressurizing the wastegate port with a Mityvac or compressor to see if the actuator moves freely and holds pressure.
3. Pop-off Valve Leak: If the pop-off valve isn’t sealing well (you noted vacuum loss around the piston), you could be losing pressurized air before it reaches the intake. Even though it’s vacuum-actuated, if it’s not sealing fully under load, you’ll get a major boost leak.
4. Turbo Spin Isn’t Enough: Spinning the turbo by hand confirms it’s not seized, but you’ll want to check shaft play as well. Excessive radial or axial play can cause poor spooling or internal contact that hurts boost production.
5. Timing and Cams: If someone did install a different cam, it could affect spool characteristics, especially if it significantly changed overlap. But even then, you should still see some boost. I’d only dive into the cam timing once everything else is ruled out.
6. Exhaust Obstruction: One long-shot—but worth checking—is a blocked or collapsed exhaust (e.g., a broken baffle in the muffler or an internal cat issue). That could kill boost without causing rough running.

I’d recommend starting with a boost leak test on the intake side (pressurize from the turbo outlet) and manually testing the wastegate actuator. If all of that checks out, then maybe consider pulling the timing covers to verify cam timing.

Hope some of that helps. You’re close—just one piece of the puzzle left.

So I’m at 4deg ATDC at 950rpm and 27deg BTDC at 4k.

While I’m waiting on the AFR I’m going to buy a better borescope and look down the intake of the turbo and see if it’s spinning. I think I can get the scope down maybe where the rubber boot is on the inlet. If it’s spinning may also see if it’s spooling up with the increase in RPM.

Process of elimination. You're checking all the boxes.

I guess it's possible that your turbo isnt spinning freely enough, even though turning by hand says it's fine. I haven't heard of a turbo siezing up unless the bearings are so shot that the impeller(s) are striking the housing. Usually before they get to that point the seals are gone and you're blowing oil smoke.

You've already checked...if you had a massive leak somewhere you would see other really poor running symptoms. And you've checked the boost recirculation manifold/piston...a logical place to look for zero boost.

How is the rubber elbow that comes off the air metering housing? I've heard tell that if aged and soft, it can collapse and severely restrict flow to the turbo compressor.

Exhaust obstructions? Are you running with a catalytic converter all plugged up?

Running out of ideas.

That rubber elbow! That thing is the bane of my existence! It sure isn’t soft! I’ve had it off and on too many times to count! It’s not hard to the point of cracking but hard enough to have me banging my head on the hood latch, cussing and tearing skin off my knuckles. I’ve actually had it just magically go on twice and have no idea what I did and no way to reproduce it! It’s a Euro so no cat not that I know that to be the reason but there isn’t one on there or an EGR. The only emissions stuff left are the 6 air injectors and the hard tube connecting them all together.

The borescope will be interesting to see what I find. I guess after using the borescope and verify it to be spinning I can check the turbo for shaft and radial end play. The manual seems to call for testing that with the turbo out but I’d think that if the turbine is freely spinning and had some catastrophic failure that it would be pretty obvious with a dial indicator even if still in the car.
I sure hope it’s not the turbo. I have to make purchases carefully so as to fly under the radar of the CFO in our house! She’s still bent out of shape due to the last project I was working on! This is the very car my dad was given prior to heading off to UT Austin and then to UTMB in Galveston. http://forums.pelicanparts.com/uploa...1748128691.jpg

Yeah that elbow is a beach! And your dads car, whoa! Very nice.