Hi, first time post on here and hoping there is someone that can help me out with this problem.

I want to try give all the information, so sorry for the long post!

2011 Meriva 1.7 (Denso type) 85,000 miles.

So I bought this car about a week ago as a spares or repair, this is a summary of what the previous owner told me his garage had already replaced these parts:

Fuel regulator/SCV
MAF
Rail pressure sensor

After this his garage told him it must be the hp pump.

I could see that these parts had been changed as the old units were inside the car, however they had fitted the wrong SCV valve as when checking the loom plug, it was just resting on the SCV plug!

The car cranks and almost starts during the first 5 seconds of cranking, but after this just cranks with no signs of firing, if you leave it a minute and try again it will try briefly again.

I have tried with easy start and this doesnt seem to have much effect and after trying to crank this way for around 10 seconds the engine kind of locks up with back pressure and struggles to turn over.

When using the easy start it caused a cam sensor code, which I swapped before I realized it was the back pressure causing the disturbance in signal between cam & crank sensors.....money wasted. I presume the crank sensor is ok as there is no code and live data shows rpm at 200 or so when cranking?

The in-tank pump makes an 'groaning noise and primes for like a minute, which seems like a long time and an unusual noise - I've had the tank of and put 12v direct to the pump which makes it throw fuel out at a decent rate - also changed the fuel filter - so presume this side of the system is ok and maybe normal for this car?

When cranking live data shows the rail pressure at around 200 bar initially and then can spike up to around 500 bar - is this why it tries to start initially and then doesnt because the pressure is too high....is that a thing?

When cranking if you crack the injectors or rail there is diesel there - I've had all the injectors checked by a local specialist.

I have installed a second hand pump complete with SCV valve from a 30,000 mile car and symptoms remain unchanged - absolute nightmare of a job off the floor!! New cam belt fitted and timing checked with marks and cyl 1 at TDC.

So the only code is P0089 with returns immediately when cleared, which points to it being an electrical rather than mechanical fault?

I have done a voltage drop test from the SCV loom plug and there is 2.5v being read between battery negative and plug negative, my understanding is that anything over 0.5v on a drop test is a problem - Could this cause a no start like I am getting.

Any advice or questions gratefully received as this car is pushing me close to the edge lol