I guess you already checked the fuel supply
Always go for the cheaper fix first.
A plugged fuel filter will make low pressure too. I always put a lift pump in the equation to troubleshoot fuel delivery issues. Add the electric pump back at the tank that way you know you have good fuel supply out of the filter(s)
Google "Facet pump" I use the low pressure (3-5 psi) pump so I don't add stress to the injector pump. Once the extra pump is in the circuit you can eliminate all air leaks and clogs


Brian Rodgers
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1989 Isuzu Pup gasser
2-86 Isuzu Trooper turbo diesels (1 good 1 bad)
Many gallons of biodiesel since 2005