No Boost... Help?

[baltimucho]

Backstory: 86 SVO - I've owned it a year. She's my 3rd. It had problems overboosting. Previous owner swapped the stock boost regulator for a Gillis valve. Ended up swapping valves, then finally just using wastegate pressure and keeping the boost around 10psi because the turbo bearings were going bad.

I had a spare turbo (from a spare SVO) that was running great at 15psi a couple of years ago. I recently swapped the out the oil-leaky turbo for the spare. In doing so, I had to remove the exhaust manifold to get the old turbo off, and ended up cutting out the EGR crossover tube and deleting the EGR. I replaced the EGR valve with a block-off plate and plugged the hole in the manifold. I plugged the vacuum line from the EGR too.

I installed everything and left the wastegate directly connected, expecting 10ish psi. I barely got 5psi. I added a Gillis valve, no change.

I double-checked the intercooler couplers, vacuum lines, etc. The car ides around 1000 RPM at 10psi of vacuum, but the car will not build boost over 5psi... and it only reaches 5psi at 5000+ RPM.

I also double-checked that the impeller is spinning freely, after having to clock the cold-side a bit.

I'm at a loss. I just open the hood and stare. Any thoughts?

[MikeFleming]

I just open the hood and stare.

BTDT. If you point at things and yell & threaten loudly it usually helps.

Sounds like you need to replace the wastegate actuator.

To properly test it, you will need an adjustable (accurate) 10 PSIG air pressure source to connect to the diaphragm nipple and probably a dial indicator to measure wastegate arm movement. The spec is to have 0.015" of movement of the flapper arm at 10.0 PSIG. Most likely you're getting 0.50", and that means the actuator spring is seriously weakened (it sits VERY close to the 1600F+ exhaust manifold and they dol;t last long at those temps).

[baltimucho]

That's what I was guessing. Since I used the original downpipe and the spare turbo, there could be enough variation that the actuator arm is keeping the flapper from sealing properly. I'm making a PVC pressure tester this weekend. Thanks!

[J. Caraco]

Years ago when I didn't know better I used 42lb inj. and it wrecked the CAT. It was plugged so bad car would boost. Still running a cat?

[baltimucho]

Yes, but the coincidence of the turbo swap makes me want to start with the turbo. I have spare 3" exhaust and hi-flow cat if it comes to that. ;-)

[baltimucho]

The flapper arm was the culprit. Fortunately, the actuator I installed had an adjustable arm. The other two I have didn't. I don't remember giving that any foresight, but I'm glad I did.

So... Boost is back! WAY TOO MUCH BOOST! This is what I was experiencing before the turbo swap.

I connect the actuator to the outlet on the I/C and I boost to 9-10 lbs, just like I should.

I throw the boost valve in the mix and the boost never stops.

I have two boost valves and they both do the same thing. I have them both as closed as possible. I hooked them both to my air compressor and neither starts bleeding until around 30psi.

What could I be missing here?