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The starter motor will be drawing a damn sight more current than the fuel pump.

I'd try a known good battery as atlex suggests.

Speed is proportional to voltage in a DC motor so if you're seeing fuel issues, it might be related to the pump running at 3/4 speed, though cranking fuel flow shouldn't tax it compared to demand at WOT.
 

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Thanks

Zero issues at wide open throttle, it's just this weird laboured cranking and sometimes losing sync. Fuelling is fine, my car is currently continuously priming on ignition and that also has no interruptions.

I have a new map to try today with different trigger edge settings as it was mentioned that sometimes "falling edge" can cause this behaviour.

My next port of call is either a new crank sensor or a new battery, I haven't decided which yet.
Laboured cranking is likely voltage related, 'losing sync' could be related to microcontrollers in the ECU browning out from the low voltage.

Two failure modes linked to low voltage, I'd be checking the high current connections and trying a new battery before I worried about the crank sensor, unless you have a known good one to swap in. If you're strapped for cash and it's one or the other, a friend's car and some jump leads would prove out the battery issue.

I've just stuck a DMM on my battery and from 12.29V with the ignition on, it only dropped to 10.5V while cranking...
 
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