[NeMachinist]

How's the lift pump pressure?

When you are cranking is there any smoke, white smoke mainly?

You are either not getting high enough cranking speed, or you are loosing rail pressure faster than you can make it.

Fuel supply 1st, then rail relief and the relief valve on the cp3 need to be checked.

Don't waste time chasing the grid heater as a problem, it is not needed exept for brutal cold below 0f.

 

[NeMachinist]

Maybe the crossover battery cable is corroded and causing high resistance.

I understand the frustration, I've been there from time to time.

You really need to confirm lift pump pressure to the cp3. Then go from there.

You can hook a booster pack 9r jumper cables to the drivers side batt to see if that improves cranking rpm.

 

[NeMachinist]

Check the lift lumpy pressure even though air dog goes directly from tank to the cp3?

Yes. Unless you are absolutely positively sure that the pump is working correctly. But only way to really be that sure is to check pressure.

If you can open the fuel system, via a filter drain, or fuel line connection, and confirm that fuel gets shot out with some gusto when you bump the starter, just need some way to prove that the pump is working.

 

[NeMachinist]

What klode said could certainly be the problem.

My way of think for any problem is to start at one end of the system and test your way through the possible problems, rather than jump to the middle based on a feeling or a hunch.

To each their own I say.