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Hello Wyatt, these truck are extremely sensitive to fuel pressure. Check fuel pressure with a guage. You have a test port on the fuel rail on the intake. Fuel pressure needs to be 55-61psi with the key on. It runs around 55 psi running and pressure increases under load. Make sure fuel pressure does not go down from 55 ever. If you have less then 55 with the key on, or fuel pressure does go down, the fuel pump is your issue and is very common with this complaint.
Your JA Expert,
The way these systems are, they require and absolute minimum of 55 psi to open the fuel injector tappets. The tappets work like a mechanical valve and release at a certain pressure. If the pressure is even 4 psi lower, the system will start having issues. The fuel pressure regulator's job is to increase fuel pressure when load is applied raising fuel pressure towards that 66 psi mark. If fuel pressure decreases, the fuel pump is the reason why. Regulators can fail, but it's usually a case where the fuel pressure will not hold, it sinks with the key on
These intervals can drive you crazy, the key is to have the guage on during the bog. You won't see anything when the truck is OK. If fuel pressure is truly ok during the bog, then we can focus elsewhere. This post will remain open for a long time, so you can jump right back with me as you need to. That maxi-injector set up, is a common failure, but I would want more evidence before condemning it.