Chocolate40 said:

Replacement low pressure pump used but working.

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Put a pin in that one.

Chocolate40 said:

Plenty of fuel flow at return to tank.

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This means the pump spins, not that it’s any good. I could wee down the fuel pipe and produce plenty of flow, but could not pressurise the system to 35 psi+... See above.

Chocolate40 said:

Live data on high and low pressure switch with in spec.

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...while it’s running ie no fault occurring.

Chocolate40 said:

4496 fuel pressure deviation was making the mil light come on.

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Chocolate40 said:

It also resets the mil light and it goes out until I hit mid rev range or load.

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These two points might suggest the low pressure sensor is intermittently failing, causing the ECU to shut off the engine to protect the HP pump. Have you wiggled the wires to it and tapped it? I might be tempted to replace it.

Also, you haven’t mentioned manipulating the ignition key. Replacing the fuel pump relay also worth it for the price.

Looking up fault code 4496, it looks like ‘rail pressure monitoring deviation’. Remove and have a very good look at the rail sensor, make, model no. Etc. Also inspect the added loom right back to the ECU.