So. A concerned question.... the ground problem I found was the eyelet ground on the frame was off from my own doing about a month ago due to me probing the harness checking the fuel gauge. With that said. The truck apparently has been running all that time without the lift pump working and I didn’t know it.. shame on me. Have I possibly caused irreversible damage to the IP. Also what should the line pressure be from the lift pump with key on and idling.
now I’m headed inside to go kick myself in the A$$ for this mistake
I will be looking into an inexpensive gauge to mount in the cab real soon because of this experience
Well as I read the whole post, I was waiting for the post where you discovered that the lift pump pressure was not good enough.
There are a number of things that matter, but the number one is good presistant high lift pump pressure. The OEM style solenoid pumps do not work at all or for long. When warm up they loose the ability to pump even more. I use the Sure Cure Lift pump solution. It comes with three pumps. One to use, one is a spare, and one is a emergency use one that is a canister style and a fuel pressure regulator that will hold and let 20 psi to be set. By the time it passes through the filter you get 16 to 18 psi at the lift pump under all conditions even wide open throttle. The emergency pump is used for mounting bracket and some hardware., but it is emergency swap use only because it only puts out 4 to 5 psi. You will hear and read that fuel pressure should be 5 psi, but that is MINIMUM psi. Even the Delco EP 158 has a spec of 10 to 12 psi though it won't hold that for long even after new.
I have an electric in cab digital readout that I use rotary switch to switch from vacuum / boost, to fuel pressure at the ip, to fuel pressure pre filter, to transmission line pressure. They all use 0 to 300 psi transducer sensors. The readout is dual display and the other is post turbo exhaust gas temperature (EGT)
It has been five years since the Sure Cure Lift Pump solution went in and recently pressure dropped to 14 at the IP. OK so what I figured I needed to change the filter.
One day it stumble started only the second time in five years. Then again a d shut off. The lift pump is really quiet so much so if the HVAC fan is running I can't hear it. I cut off the fan turned the key on and it sounded weak. Then it started on the fifth try. The next morning no start, and no lift pump sound at all. This is why the Sure Cure Lift Pump Solution comes with a spare. Checked for 12 volts at key on and swapped the lift pump which took 30 minutes, and started it right up. Now it was back to 18 psi at the IP.!!
Since I used to work with a Diesel shop that specialized the Stanadyne pumps, it is important to understand the pump expects about 12 to 18 psi to perform best. At about 10 to 12 psi the return check valve on the top of ip opens to begin to let let fuel return to the tank. The purpose of that is to keep the timing wheel tank full of cool recirculating fuel which supposed to cool the PMD that mounted on the side.
But here is where the problem started where GM wod not listen to Stanadyne that the solenoid lift pump they selected would not work for the DS4. GM did not understand the electronic nature needs 18 psi to work properly for long life. The PMD also called the Fuel Solenoid Driver or FSD is a poor ideal to use Power Transistors ( the two round things on the underside of the PMD) as a voltage regulator switch to drive the the Fuel Solenoid which is on the rear of the IP which is effectively the throttle that is actually pressure controlled. FUEL pressure controlled, and it is kept closed by a spring and assisted open by the Fuel Solenoid which driven by the PMD. The PMD is supposed to to assist only to open the plate more to increase engine speed. When there is low fuel pressure in the IP, two things happen, first there is no fuel to fill the optical sensor tank area to cool the PMD and second the the switching transistors are OVERWORKED trying to keeping the throttle plate open to try and increase engine rpm. This overheats both the PMD and the Fuel Solenoid which also shortens the Fuel Solenoid life also. So this the DS4 death spiral. The PMD relocation is a band aid. Minimum fuel pressure is also contininung the death spiral.
It is all because of the lift pump. The Sure Cure Lift Pump solution has in line axial pumps but the emergency one is a canister motor driven wet pump.
When you put 18 psi at the IP you should notice a light foot on the accelerator will make it take off and it will pull like a gas engine if everything else is right.
It sounds like there are turbo and waste gate issues. The waste gate solenoid or actuator or map sensor may have issues assuming you have good vacuum. An OEM setup will never go over 10 psi. It will open the waste gate using the map sensor and waste gate solenoid. As others have said the wicked wheel will spool pressure faster but a proper system if stock will work with the ecm, timing and fuel input. pressure
I would get a good positive in line true motor driven ift pump that is dependable first. Most of the problems may go away like you realized the lift pump was not working. Also even the OEM solenoid pump from cold start pumps strong and then gets weak when it warms up.
Also my TDC offset is - 1.25 and it ran like crap until I did the key on key off procedure
. I did take some time cleaning up the engine compartment while striking up the bbq pit!
I couldn’t have done it all without everyone’s help here. 
