Right, i've got a 4x4 cosworth with a ahmed bayjoo stage three chip which was fitted by Harvey Gibbs by previous owner.

It has a switch for high/low boost.

My problem is that it works fine when on low, but on high it doesn't boost to what it used to and stutters. It boosts up no problem with a bleed valve attached instead of the amal, which has led me to think it is something to do with the amal/amal wiring. I have checked the amal function and this is fine.

I have figured out that the switch breaks the earth which goes to the amal valve. Now this is where my problem starts. The wire which usually goes to the amal from the ECU (brown with yellow tracer) has been cut and the switch inserted here, but only the end going to the amal! - The other end is not attached to anything - The output from the switch is attached to a thicker brown wire which is part of the original harness for the ECU but cannot see where this goes or where the other end would have gone.

Surely this must go to something which controls the switching of the amal to control the boost, but where? Why has this been done and the ECU bypassed. I find this really strange! What could be done on the other end of this wire, as i'm assuming this is what's at fault Could i just connect it back to the ECU?

If anybody has any experience of this then i'd love to hear your responses as i hate using a bleed valve.


Thanks in advance.

Pete.

 

The common low/high boost mod is to simply insert a switch in the wire between the amal valve and ECU pin 16. Sounds like on your car, someone has simply connected the amal valve wire via the switch to a permanent earth.

solution for your car :
1 unplug from the switch the wire between the switch and the thicker brown wire (probably an ECU earth)
2 connect a wire from ECU pin 16 to the switch (the original wire from the switch to the amal valve is OK)

 

Thanks Jon, i'll give that a shot. Does this mean i'll be back to factory standard boost or is this normally programmed into the stage 3 'chip'?


Cheers,
Pete.

 

What you'll end up with is (depending on switch position) either max boost as per the chip (obviously as long as the rest of the components are in good orderand adjusted correctly) or a boost limit determined by the spring rate and preload on the actuator (probably somewhere around 7-10psi)

 

Ok, i hope that's the case. Any ideas why they would have connected the other side of the switch to a constant earth in the first place? I would have thought that this would just have made the car boost infinitely as the solenoid in the amal wouldn't be opening and closing to control the boost?

Cheers,
Pete.