fuel pressure ok at 9psi, 10psi it pulses.
 

Seems like I'm on the threshold of either my wastegate not holding closed or my fuel pump doesn't work properly at higher boost levels. I'm using an 8:1, emanage, 310cc injectors and the stock fuel pump. When I turn up the Hallman MBC to try and reach 10psi (I'm currently running 9.5 for this reason) or 11psi, my fuel pressure (according to my wideband and fuel pressure guage) pulses between 65psi and 80psi (stays at 80psi constant when I'm only at 9psi). It's not enough for my wideband to register anything dangerous, but I can feel the car shimmey. I have a few ideas, but I don't really get why this is happening. Everything happens so fast, I don't get a chance to see if my boost is bouncing too. I'll have to play around more. Is anyone using a "helper spring" for 10+psi? If so, and it's working well, where did you buy it?

Oh, here's my current map.....I may disable my airflow map as this may be causing this as well. I'm using the tps input for my wideband, but I'm not using Olderguy's autotune, so my fuel can only adjust leaner automatically....but this would be controlling the flow, not pressure...mmmm. My map is second last in the link below.

https://www.miataturbo.net/forums/showthread.php?t=580

I can hit 15psi without a helper spring. The actuator works when the Hallman is bypassed at 6.5-7 psi.

Doubt it's the mbc as I can also get to 15 psi with el cheapo home depot mbc. I use a helper spring to add tension to the wastegate to prevent it from opening a little early so I can spool a little earlier and it helps me hold 15 psi to redline instead of slowly dropping off at the very end. FWIW, I got a spring from the local hardware store and chose based on length and tension as there was a whole section of different springs. If you do go that route, you can always attach it to the wastegate on one end and a eyelet bolt on the other so you can adjust tension with the bolt.

Maybe an emanage log during the shudder will shed some light as well?

you could also have a leak from the manifold to the turbo this happened to me i thought it was the WG until i blew the gasket all the way out spool was alot slower and the pressure wouldnt go as high as it should have. just my 2 cents

I had kinda the same prob. intake was loose. feels kinda wierd!!! Try to issolate the prob a little better.

I'd check the manifold for leaks. I had one on mine that just progressively got worse as time went on. Was really easy to find using a piece of vacuum line like a stethascope. As soon as I did that there was a very obvious leak at the manifold -> tubo flange.

Jay