Due to various issues with my engine over summer, including oil leaks, I decided to give it a proper overhaul. Got the heads skimmed, new valve seats, guides, HGs, etc. Also new bearings, rings and so on. I also replaced the turbo cartridge with a new one. The fuel pump is new too. Since going back in the car I've been gradually running the engine for a few weeks, so treating it pretty gently. I've now given it some new oil and started to push it a bit harder. However, it seems to be lacking a lot of power when the turbo should be boosting.
It starts to feel really flat above 3.5-4k rpm, and bogs down when applying power. I also often had a similar problem before the rebuild, so it's unlikely to be anything I've touched with the rebuild. However, I'm not sure what to examine first. such as injectors, coil packs (spark plugs are new), exhaust system, turbo vacuum gubbins?
Everything on the engine is standard (2005 WRX EJ205), so the ECU shouldn't be fighting against anything.

 

Get a Tactrix cable or similar and start logging what is happening. Otherwise you are simply guessing and spending a lot of time and money swapping parts. I've had similar issues on that engine and it was a combination of fuel pump and spark plugs. However, you've already replaced those (could still be that the new parts are faulty). Can you confirm that it's even making boost? Something as simple as a worn actuator will limit the turbo to mechanical boost only, which is ~7psi. As I say there are many reasons why the engine could be underperforming - if you can measure what the engine is doing (boost, fuel, timing etc) then it will be a lot easier to identify the issue.

 

It could be:

You aren't making any boost

You are making boost but there isn't enough fuel:
Fuel pump
Fuel filter
Injectors

Ignition issues:
Spark plugs
Coil packs

Timing issue:
Faulty knock sensor or genuine knock issue causing the ECU to pull timing

Cam sensor
MAF
Air/vacuum leaks
Blocked exhaust
ECU

Or a combination of any of them. Some should throw fault codes but many won't. That's why I suggest if you could log the values of these when driving, it should easily point you in the right direction, even if it's not obvious what is causing the fault. Some of these you can log just with an OBD2 app on your phone.

 

I had a go with logging on my Autel ODB2 scanner on a drive today. Why is it you can rarely find a clear stretch of road when you want to have a test drive? Weirdly the car ran much better today and on the two occasions where I had enough space to accelerate firmly it seemed to go pretty well, much better than before. So something seems to be intermittent with the engine.
I've tried to have a look at the log file saved from the scanner using a bit of reverse engineering on the file (I don't have any Autel software to use), and nothing really jumps out with the parameters I logged which were: Load, MAP, RPM, VSS, MAF, and TP. The MAP values seem to look pretty high when I was accelerating, so it did seem to boost on this test run.

I'll try and get out for another run soon and try some other parameters, such as timing. The low sampling rate of the ODB2 values isn't very helpful as it tends to hide any hiccups in the power delivery.

 

I decided to try some old school analogue monitoring, which is a bit more real-time than the ODB2 logging. I've fitted a mechanical boost gauge to see what's going on there. On a drive today I did notice the boost bouncing around quite a lot when I put my foot down. In 2nd gear it picked up to 1.0 bar, but then flapped down to 0.5 right away and the engine seemed to bog. It doesn't always do it, and seems quite unpredictable. I also need to place my boost gauge (not planning on a permanent fitting) is a more visible location to observe it better.

I also tried measuring the fuel pressure with a gauge today. With the engine off, but fuel pump primed it sat at 43psi. When idling it only dropped to about 39-40psi, which isn't a big a drop as I would expect? When I removed the vacuum hose to the regulator it sat around 43psi. I couldn't put the engine under load to test it under boost as the gauge was by the fuel filter. I wonder if the lack of pressure drop at idle suggests a problem with the FPR?

 

I would be checking for vacuum leaks on the small pipes to the regulator and any other associated ones. The fuel pressure should drop a bit more than that 1:1 on boost and idle is about the run of it.