i have a sierra 4x4 on a j the problem iam having is trying to set the boost, i tried driving up the road in 3rd gaer at 3000rpm and foot on the brake and set it to 16psi as stated in the paperwork with my msd chip.
i thought that was it but under normal driving as the revs pass 3000 the boost starts to go passed 16 and by the time iam at 4500 the boost is up to nearly 20psi
so i thought it might be amal valve or actuator these have both been changed and i have checked the wastegate is not stuck
if i sef the boost to 16 at 4500rpm then when i floor it at say 2500 i only get 11-12psi ,i have also put the actuator pipe straight to the turbo but no different
it has a -31 collins actuator stage 1 chip and scorpion exhaust but other than that is standard
any ideas!!!!!!

 

Sounds like your actuator is overloaded. How much preload have you got on it? Should be no more than 3mm ideally but a MAX of 6mm.

 

hi thanks for the reply with regards to preload when i put the actuator on i put it so that the rod was as you said about 3mm at first and tried it but that only gave me 5psi so shortened the rod to get my 16
should i have used a pump to give the actuator 16psi first then fit the rod, sorry to take up your time

 

Sounds like your AMAL valve doesnt work mate. You cant compensate for that on the actuator. Please unplug amal and let me know what difference it makes to your boost. Should add at least 50%

 

the 5psi was with no amal valve just pipe from turbo to actuator so i could eliminate everthing else
i understand it hard to tell with out seeing it i do appriciate any advise

 

Put the amal valve back on and your problems will go away mate.

 

ok will give it a go thanks

 

found the problem purely by chance i was adjusting the preload on the actuator then took it out for a spin and had no boost looked at the actuator and as i touched it it snapped shut ,found it is getting suck only very occationally so will have to get the turbo rebuilt
thanks for the advice

 

The gate not shutting is a seperate issue mate, it usually causes NO boost. As you have already found. It may however also cause boost creep, but the fact is, with that actuator fitted you must run external boost control, you have no other safe option.