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The last few years my se has been a right little turd and hasn't been running correctly. Basically it will not produce boost unless it's at the very end of the rev range and that will only produce one or two psi of positive pressure. I've been pretty fed up with it and parked it up untill I had the time and money to go down the aftermarket ecu path..

I draged her out of hibernation and tried to do a quick boost leak test. Low and behold it won't hold any pressure. I've pulled off the intake and plugged the silicone elbow that comes off the turbo inlet with a pvc cap, I have also disconnected the intercooler piping before it heads down behind the passenger's headlight to the intercooler to try narrow it down. It will build pressure but not hold it. I've sprayed all the rubber hoses including the black hard pipe that bolts to turbo with no luck.

I'm at really at a loss to what is going on.

Faulty blow-off valve?

OK, we need more context as I am really struggling to work out what you have done here.
So you have removed the intake(airbox I assume).
Blocked the intake pipe to the turbine, Black rubbery thing.
Disconnected the hot side intercooler piping behind the passenger headlight. I'm assuming the silver metal pipe directly behind the head lamp from the rubber one.

I'm assuming you are doing this without running the engine to do it right?

So where and how are you injecting air pressure to do the test?
My guess based on what you have blocked is that you are testing from the hotside intercooler pipe to the turbo, but I honestly cannot tell.
Can you draw a simplified drawing of what you have done?

Basic info to start with; Is it stock? Any engine mods?

A quick scan of your posts shows this thing has been a dog for a long time, it seems. Drawing a line through your issues tells me that we are probably looking at multiple things here - and as a result I doubt that doing this remotely is a good use of our or your time, so my suggestion is that you seek out a tuner/workshop, and get the car thoroughly checked out. There must be a few SEs over there whose owners can point you at someone who knows about the SE's little quirks? I presume you are a member of the local MX5 club over there, they should be able to point you in the right direction, whether it is for DIY or a suitable shop.

I never had big problems, but the 'bog' was annoying. I just bit the bullet, gave it to a highly experienced workshop and it came out with a new ECU and no bog, not to mention better performance and improved drivability - all on the stock turbo. You don't have to go that far, but a decent shop is going to fix it a lot faster that you can, albeit at some cost. If you want to persist with DIY, others may be able to help.

Good luck

Hmm only making 2psi high in the rev range is one hell of a leak, if that's what your issue is. That size leak would be very obvious if you inspect all the rubber joiners thoroughly.
As others above have said, hard to diagnose without more info, but I guess other places to look is wastegate and the turbo itself.

Steve Lee is/was the MX5 guru in Perth - last I heard he had a mobile mech business, plus also Ross James - see following for details of both: viewtopic.php?f=18&t=77326&p=938994&hilit=%27steve+lee%27#p938994

Mr Sexy wrote:The last few years my se has been a right little turd and hasn't been running correctly. Basically it will not produce boost unless it's at the very end of the rev range and that will only produce one or two psi of positive pressure. I've been pretty fed up with it and parked it up untill I had the time and money to go down the aftermarket ecu path..

I draged her out of hibernation and tried to do a quick boost leak test. Low and behold it won't hold any pressure. I've pulled off the intake and plugged the silicone elbow that comes off the turbo inlet with a pvc cap, I have also disconnected the intercooler piping before it heads down behind the passenger's headlight to the intercooler to try narrow it down. It will build pressure but not hold it. I've sprayed all the rubber hoses including the black hard pipe that bolts to turbo with no luck.

I'm at really at a loss to what is going on.

I'm in Perth. If you PM I'll help and have a look.