4.2 D4D intermittent hesitation

[aurumdeus]

Hi, I've got an issue with intermittent loss of power. I've read everything that I can, and it's none of the usual suspects.

Sometimes the engine will behave completely normally, no issues whatsoever. However sometimes when I go to accelerate the engine will go completely flat. It stays that way for 2-8 seconds, then the power instantly cuts back in again. 

Live data shows that the fuel pressure drops massively when the engine goes flat, and then the instant the fuel pressure comes back the power comes back again. So I'm sure that it's low fuel pressure that's causing the loss of power. The question is why the fuel pressure tanks for several seconds, and then comes back in again.

I swapped out the SCV valves with genuine Denso ones - no change. The fuel filter is new. There are no error codes being produced. 

The live data gives the fuel pressure, but it won't give the target fuel pressure. however it does give pump VMC or VCM angle, which seems to correlate with the fuel pressure. I think it's the angle that the SCV opens in each rotation to control the volume of fuel entering the pump, so I think that it can be equated to target fuel pressure. This also behaves the same as the fuel pressure. That and the lack of error codes makes me think that the issue is the ECU deliberately dropping the fuel pressure. The question is why it would do that. I can pump the accelerator 5 times, and maybe 3 times it does this, 2 times it's normal. 

Has anyone encountered something like this?

The car has a new turbo and has no issues with generating boost pressure. The EGR has been stripped and cleaned. The throttle position sensor is also new.

[Tumezi]

Did you make injection pump initialization after you changed the SCV valves? It is used mostly when you change the pump to learn how the pump works (slight differences beetween pumps and valve), To control it correctly.

[aurumdeus]

No I didn't do that - how is that performed?