strange let boost problem

[alan b]

hey guys put an let corsa back together two days ago and the boost was all over the place, it had a bleed valve and the boost solenoid wasnt connected. so i reconnected the boost solenoid and took out the bleed valve. theres evo 5 v-maxx chips in it so we went to set the boost. we got it to hole 1 bar and overboosting to 1.2-1.3 bar. sorted! not quiet as while in forth foot hard down it held 1 bar for about 5 seconds before it just dropped to .5 bar and now in any gear it wont come up past .5bar? i checked boost pipes all the vacums, actuator and the throttle body for leaking but they all seem fine!? any one have any clue whats wrong with it?

[meritlover]

is the actuator arm actually moving freely and closing with fullness?

[alan b]

ya the actuator is fine.

[meritlover]

perhaps the wastegate is cracked or the penny is melted away to heaven? try and run it with the boost sov bypassed (go straight from take off point to actuator) and see if the boost will go higher than .5bar. although about 7.5 psi sounds about right for a factory actuator. perhaps there is a fault/blockage with the boost sov or the blockeage in vent hoses??

[craig green]

Checked Amal valve?

Is the fuel pressure suitable for the EVO 5 chipset? The boost will drop off as you were experiencing overboost.

[AlanH]

my r5gtt had that problem, boosted up in first and second ok then when you hit third boosted a bit then dropped right off. kindly spat the bearing outta the turbo just after that an f*cked it lol

[alan b]

ya it had an uprated fuel pump and reg, it wint boost past .5 bar now in first second, if you build it up slowly in third or forth itll go to a bar, then floor it itll starts to drop off again.

[meritlover]

is there an over boost valve that is configurated wrongly?

[craig green]

Overboost is controlled by the AMAL valve.

www.max-boost.co.uk (http://www.max-boost.co.uk)

[meritlover]

i understand now mr green. it sounds like the overboost is plumbed back to front.

[craig green]

My guess.

[Stoo]

limp mode?

[meritlover]

that is a good point. if the ECU senses detonation(or the det sensor is OC/SC ) it may jump to a different map and close in the overboost valve like the VG30DETT does.

[alan b]

wiring up ecu light today to see if it is limp mode, amal valve isnt plumbed backwards, just checked it, belmont turbo off here gave me a vacuum diagram!

[craig green]

MIG or Vauxsport are far better resources for this engine tbh.