Brakes hold pressure until car is turned on

[MoonstoneWild]

Hey everyone, here's a puzzle:
So the turbo on my d40 blew up. Replaced it with a Japanese ebay turbo and works great. However before I pulled the original turbo out I gave the engine bay a wash and unfortunately water got into the brake reservoir and destroyed the master cylinder so had to replace that.
Before now, it was realised that applying the pedal actuates the waste gate vacuum on the turbo. So today I replaced the vacuum tubing connected to the turbo.
Now the problem follows that when the car is turned off and you apply pressure to the brake it behaves like every other car turned off and builds up pressure. When the car is turned on the pressure disappears and the pedal descends to the floor.
Prior to today, before I replaced the vacuum hose. The brakes worked but would lose vacuum if pressed repeatedly before stopping. Now after replacing the vacuum hoses the brake still hold pressure when the car is off but now when on, the brake pressure disappears until the pedal touches the floor, brake barely working.
The brakes have been bled to infinity and the turbo valve solenoid (14956u-eb70b) was tested following this video: and appears to work.
We have a advanced obd2 reader that can run individual systems in the car and in an attempt to bleed the abs pump, the pump runs and then a prompt appears saying that, that function is not supported
We are at a loss with the only feasible idea being that a vacuum is being created in excess. Any advice would be greatly appreciated! Thank you

Nissan navara d40 st thai build, yd25, manual

 

[Old.Tony]

Let's try and straighten things out here.

The D40 shouldn't have a waste gate turbo, it should be a Garrett 2056V variable vane turbocharger and it should have a round gold-ish widget facing uppermost attached between the two turbo halves and a vacuum line should be connected to this. The other end of this specific vac line should go to a Boost Control Solenoid (BCS) which is what you've pictured above.

The BCS is controlled by the ECU at 100Hz. You can check the signal on an oscilloscope if you suspect the ECU isn't supplying a good signal to the BCS (I've never heard of this happening).

There should be a few sections of vacuum line, one of which goes across the top of the motor to a small metal pipe, this then leads to the vacuum pump itself.

The vacuum pump also supplies vacuum to the brake booster. Inside this is a diaphragm that pulls and increases the braking force applied to the master cylinder (basically).

Pressing the brake should NOT do anything to the turbocharger, but taking your foot off the throttle SHOULD.

Any of that vac line could be suspect. If it's loose or able to turn/spin on the connection then you have a vac leak (hardened hose won't seal and these aren't clamped, they're 3mm ID hoses that only push-fit on).

Vacuum leaks are a common issue and it's well worth making sure all of them are in good order (did you replace ALL of it?).

Over the years, I've heard of a COUPLE of brake boosters failing (vac diaphragm). I wouldn't assume this was the fault immediately.

On my bike, I had a problem with my rear brake pedal slowly dropping to bottom, and discovered that the front left caliper had a small amount of air in the line (Goldwings have a rear brake that is linked to the front left disc, the front brake lever only operates the front right disc).

So here's what I'd do.

Double check every piece of vacuum hose on the system. It has to be flexible, and NOT loose on any connectors. Replace any that are suspect. I use silicone based hose from Supercheap Auto:

https://www.supercheapauto.com.au/p...um-hose-black-3mm-id-x-3m-ssvh33m/589725.html

I'd then closely examine the brake cylinders while the brake pedal was being pressed (takes two people). Look for any hint of leaking. Make sure the pads are being pressed firmly against the disc and not letting go (a sign of air in the line).

When I bleed the brakes on my bike, I used a piece of clear hose that I fed into a small glass bottle so the hose was at the bottom and pressed the brake lever and loosened the locknut while I had pressure on, and locked the nut up before the brake lever finished its travel. I repeated this until the hose was filled with fluid (no air bubbles). This prevents the system sucking air back in - it was all I could do, trying to bleed the brakes on my own!