hi folks, i've been having a few turbo boost issues with the 1.8T engine (agu engine code)

 

it's doing something quite odd and not boosting properly, basically it is my understanding that when the N75 is unplugged but still plumbed in you should still get a baseline amount of boost as set by the spring pressure in the wastegate actuator, however i'm getting zero boost on the gauge when the N75 is unplugged, the vacuum level does exactly what i would expect too and appears ok

 

when the N75 is plugged in i'm getting a good 10psi of boost on the gauge all the way to the redline,

 

i've checked over all the non-return valves and oil breather pipes etc, all the vacuum lines are all legit, and as far as i can tell there are no boost leaks from any of the charge pressure pipes or intercooler, also tried a different oem re-circ valve instead of the forge motorsport one that was on there.

 

this does strike me as being odd because there would be no chance of holding 10psi if there were a major boost leak, the maf is working correctly as per the logged air mass under load and the N75 does work perfectly because i've tested it on another vehicle, there's no missfires or hesitation, i've also tried connecting a hose directly from the top charge pressure pipe staight to the wastegate hose to double check and there is literally not even an ounce of boost at all, you can hear the turbo spooling at low speed as you would expect to at light loads but the boost just doesnt build up..

 

i dont believe this is an ecu/electrical fault, maybe my brain is not working right because i can't figure out why it would do this, the possibilites i've though of are maybe a mechanical fault with the turbo itself, possibly the wastegate is jammed in a partially open position or something subtle like that, maybe the gate isn't shut properly? but i wouldnt have thought that the gate wouldn't be big enough to allow that much exhaust gas to bypass the turbocharger? and like i said it makes 10psi when the wastegate control pressure is modulated by the N75 valve.. so what gives?

 

i've not touched the control rod for the wastegate actuator ever so as far as i know it should be set up exactly as it should be, is there a recognised method of checking and adjusting this? the space behind the engine is very limited on this so it would be tricky to reach.

i'm surprised nobody came forward with any suggestions to this.

 

anyway, an update, the wastegate is leaking inside the turbo, allowing exhuast gas to constantly bypass the turbine, there is also a few cracks around where the little flapper poppet valve thing seats against the turbo.

 

another absolute pig of a job to tackle changing the turbo, it's a tight old fit in the felicia engine bay, might be better off dropping the engine out