sorry I have been busy lately and haven’t had time to work on the car , what size vacuum line do I need to change out the old ones ?

 

I believe you wan 3mm and 6mm internal diameter.

Note: not all silicone hoses are created equal, The ones sold to me , by a reputable shop, turned to american cheese in quick order.

I ended up using sheaved industrial lines. After about 7 years the rubber crumbled to dust within the sheathing

Mazda was making available OEM vacuum lines through their continuation program.

A set of maybe 19 pieces might cost US$700.

The advantage is the pieces are all preformed, which makes installation more intuitive and easier.

Also your engine bay will look original.

Replacing dud solenoids with 30 year old used solenoids, is not likely helpful in the long, or maybe even short, run.

Every time you have to disturb the rats nest, you compound the damage.

Further, you really must consider a new emissions harness, if you have an original, and very crispy, example.

So this all adds up to about $4000. Sorry.

You may also want to collect spare:

ISC solenoid valve
MAP sensor
TPS
Coils
CAS
Etc.

Maybe buy several when you see them cheap.

(Hint: look up the cost for NIB/NOS examples.)

 

You can probably grab a discarded rat's nest quite cheap (if not free).

Get one of those and practise on it, before disturbing the one in your car.

Note the vacuum hose diagrams you see (including in the FSM) are no where representative of what you will actually encounter.

Most of the hoses are much shorter than what the diagrams show.

In the more representative diagrams in the FSM, it looks like the illustrator just gave up and went home.

 

To exaggerate my point, here is the rat's nest of the 20B I am reconstituting for shop display.

 

Attached is the Service Highlights page on twin turbo operation.

To be achieving constant primary boost but intermittent secondary boost, it indicates an issue with the Charge Relief Valve or some boost leak between the outlet of the secondary turbo and the charge control valve.

I know you said you replaced your charge relief valve, and tbh the internet seems to indicate they have a low failure rate, but it will be good to sanity check it anyway


More critically here I think is to test that, without vacuum applied to Port A that air cannot pass between port B and C. If the valve is faulty and staying open when it should be closed, or otherwise letting air past without an input at port A, then it is dumping all your boost back into the air cleaner in secondary boost mode.

Boost Leak
Again, for your to be getting primary boost even when your secondary boost issue appears, I believe it rules out everything except the bit between the charge control valve and the 2ndary turbo.
The only things that can leak between those two are the hard gasket connecting the 2ndary turbo pipe to the turbo, and the short 90deg rubber hose that goes from the metal pipe to the charge relief valve.


When doing my overhaul, mine wasn't leaking but it was so crusty and old that even clamped down it could swivel on its post. I ended up replacing it. This hose in particular is subject to a lot of exhaust side heat, if anything is leaking I would put my money on that.
N3A1-13-765(Secondary Charge Hose to Charge Relief Valve)
2 of NF01-13-735 (Clamps for Scndry Charge Hose)

If both your new charge relief valve is behaving as intended and you have verified no leaks in this short length of secondary turbo plumbing, then you have a rats nest/controls problem and you probably have to take off the UIM.

 

I was having similar problems with no secondary boost and went down the rats nest black hole. I found my TCS connected to the ACV had 0 ohms so I feel that is my smoking gun. I went ahead and ordered all new solenoids and I am redoing all of my vacuum hoses. I haven’t put everything back together so I cannot tell you if that fixes my problem but in theory that would give me my problems.

Mazdatrix has vacuum hose for sale for a competitive price as well.