LOW FUEL PRESSURE - out of ideas! HELP

Hi all,

New member of this forum, have been an MPS OC member for a couple years in the UK now and have a fully bolted BNR4 mk1.

So in September last year I got an issue with low fuel pressure, sitting at 40-60PSI on idle and pushing to 100PSI when trying to drive - the car is undrivable at the moment, zero power and very stutter, however it will sit and idle all day with no hiccups at 50 ish psi. I also had a code P0091 which is "fuel pressure regulator control circuit low voltage", but somehow this has now disappeared but the symptoms have not. So far I have tried -

Swapping whole HPFP with another club member
Relief valve (twice just on the off chance that I bought a 2nd hand one that was also ruined)
fuel pressure sensor
In-tank fuel pump which contains the regulator its self

Any other ideas? it has been off the road since September and im forgetting what its like to drive!

 

Damaged wiring between the spill valve solenoid and the Ecm, possible bad ecm. You've checked everything mechanical, so the issue has to be electrical.

 

What ended up being the issue?