Boost solenoid.
Turbo Mini Forums

I recently read in a poll how it was posible to remove the ECU and use the boost solenoid as a 7.5 psi bleed off valve. I have remove the ECU and am just running on the the waste gate at about 4.5 psi. Could someone please elaborate on how exactly how to plumb and wire up the solenoid to give 7.5 psi boost at the flick of a switch.

i'm guessing all you'll need to do is plumb the boost solenoid into the same place it is as standard, then just give the solenoid 12V with a switch and it should up the boost? basically doing what the metro did but you can control when it does it.

So basically when the switch is on you have 7.5psi and when it is off 4.5 psi? Any idea which side of the solenoid is posative.
Thanks Dan

it doesn't matter which pin you use as positive on the solenoid.

Team Racing

I am not totally sure as I've never messed about with the boost solenoid much, but my understanding is that rather than it "opening fully" to give 7psi on the metro, it receives an oscillating signal, so it opens and shuts very rapidly, and by doing so, only allows enough boost to leak off for actual boost pressure to reach 7psi. If you plumb it up so that you switch it and it opens fully, you will make excessive boost, as the wastegate will never open, due to the volume of air that will pass the solenoid.
One way it would work however, is to put an adjustable throttling valve AFTER the boost solenoid, so that when you switch it open, there is a restriction as to how much air will pass the solenoid.

from my experience, the boost solenoid only bleeds off around 4psi

Team Racing

Im with tom thats the way I understood it worked

Now I am really confused. If the solenoid opens fully when operated should I be able to wire it up and when the power is on blow air through it? If this happens am I better to use a bleed off valve?
Also where is the best place to plumb in a boost guage to check exactly what boost I am getting?

plumb the boost gauge in the inlet manifold.

then id put a restictor in the pipe between the actuator and boost solenoid (or on the vent of the solenoid, could use a bleed valve) and keep opening it until when you open the solenoid (simple on or off) then you get the desired result.

although i think jim is saying it will only bleed a max of 4psi above that of your actuator off. i.e. a 5psi actuator would give 9psi with it fully open.

the metro did modulate it to get 7psi. but by the sounds of things they engineered a safety factor in incase it stayed permanently open, i.e. with a 4psi actuator it wouldnt go over 8psi.

Connected the solenoid to 12V it appears that it is either open or shut. Is it possible that the ECU varies the voltage to proportion the bleed off?

I beleve the ecu pulses the valve, it is not variable.

Team Racing

Yes, I also think this, the ECU rapidly opens and shuts the valve to create a variable bleed off.

Thanks guys, seems like it may be a whole lot easier just to fit up a bleed valve.

bleed valves work for 99% of us

Team Racing