Fuel pressure issue and P0456 - 2004 4.0

[BusterJeep]

New member, old Jeeper. I have been perusing the threads here and have found bits and pieces of information but nothing seems to really hit on my problem. Any advice would be appreciated.

2004 TJ X w/150k on the clock. Currently on my 4th fuel pump. OE died at 115k. Replaced with DFG1221 @ 115k, 121k and 127k. Since going to the DFG1221 I get 6-8 months of perfect starts. Turn the key and it fires right up. But, with all three replacement pumps, I eventually started getting rough starts or long starts (i.e. priming the fuel system multiple times with the key ON/OFF) and soon after the P0456 CEL shows up. I have been limping the last pump install as I can always get it to start (knock on wood) but I think the pump is probably on it's last leg. Sometimes the P0456 will clear on it's own. Other times I pull the negative battery cable for 30 min,

Fuel line from fuel rail to tank is brand new as of last summer. Had to replace it after a catastrophic disassembly of my transfer case at 65mph severed it. Fuel injectors get pulled every 50k, cleaned, new filters/o-rings, which was done last week. No leaks on the rail, injectors or fuel line.

So here is where I sit. Fuel pressure seems to be the lynchpin in this whole scenario. Fuel pressure while running sits at 30. As soon as I turn the engine off, the pressure drops to zero, immediately. Priming with the key I hear the pump do the normal 1-2 sec prime but the pressure needle barely moves off zero. Jeep eventually starts and runs fine on the road.

I injured my shoulder a few years ago and need to find a permanent resolution to this problem as this is the last time I want to drop the tank. I am probably going to add an access hole in the tub while the tank is out but could use some advice on the pump. I know the Bosch 67726 assembly is no longer available but the pump itself 69316 can still be found. I really don't have a lot of faith in the DFG1221 anymore but it seems to be the go-to I have found on many forums.

So....
1. Any recommendations on pump assemblies aside from the DFG1221
2. Has anyone rebuilt the DFG1221 by replacing the pump with the 69316
3. Any recommendations on a replacing the regulator on top of the assembly
4. Has anyone found a suitable inline regulator I can put upstream on the frame rail to help stop the drain-back into the tank
5. Any other suggestions, advice or knowledge

 

[RMETeeJay]

Welcome. According to the FSM, your fuel pressure should be at 49.2 psi +/- 2 psi. If there was no debris seen in the fuel pickup, I recommend checking that you're getting correct voltage/current at the pump connector before assuming it's the cause. Did you switch over the filter/pressure regulator housing to the newer pumps? I seem to remember reading that it's best to install pumps into your older housing.

The evap code may not be related, unless a small fuel leak is affecting fuel pressure (which can trigger that code). If no fuel leak is seen/smelled, then check the evap hoses, purge valve, vent valve and canister. I made a cheap smoke tester that works great for finding vacuum leaks using one of the designs I found online. If you did a body lift, check the filler tube clamps.

 

[BusterJeep]

Welcome. According to the FSM, your fuel pressure should be at 49.2 psi +/- 2 psi. If there was no debris seen in the fuel pickup, I recommend checking that you're getting correct voltage/current at the pump connector before assuming it's the cause. Did you switch over the filter/pressure regulator housing to the newer pumps? I seem to remember reading that it's best to install pumps into your older housing.

The evap code may not be related, unless a small fuel leak is affecting fuel pressure (which can trigger that code). If no fuel leak is seen/smelled, then check the evap hoses, purge valve, vent valve and canister. I made a cheap smoke tester that works great for finding vacuum leaks using one of the designs I found online. If you did a body lift, check the filler tube clamps.

Thank you.

I have not checked the voltage but will definitely check it tomorrow. It did not occur to me that may be an issue in the pressure. As for the assembly, I did not rebuild the factory unit. I replaced the OE with the DFG1221 assembly as it was easier and seemed to be the best option given the reviews five years ago. Had I known then what I know now, I would have just replaced the pump and not the whole assembly.

The evap code only pops up when I have more than the usual issues starting the engine. If I clear the code, or on the off-chance it clears automagically, it does not return until I have a hard time starting the engine.

When I tested the pressure yesterday, I had no pressure in the fuel line at the rail within a few minutes of shutting the engine off. As the 2004 fuel rail does not have the shrader valve, I have my own test line that goes between the rail and the fuel line. After inserting my test line, I primed the line multiple times and started the engine. It started roughly, of course as it had to burp the air out of the test line. Once running it pegged at 30 at idle and did not move when increasing the engine speed. The pressure dropped to zero immediately when I turned the engine off. I primed the line a few times with the key ON/OFF but the needle never moved above maybe 2. I am pretty sure the regulator/check valve is not stopping the fuel from siphoning back down the line.

 

[RMETeeJay]

Here's a recent thread with some pump recommendations:
https://wranglertjforum.com/threads/fuel-pump-options.75394/

 

[BusterJeep]

Welcome. According to the FSM, your fuel pressure should be at 49.2 psi +/- 2 psi. If there was no debris seen in the fuel pickup, I recommend checking that you're getting correct voltage/current at the pump connector before assuming it's the cause. Did you switch over the filter/pressure regulator housing to the newer pumps? I seem to remember reading that it's best to install pumps into your older housing.

The evap code may not be related, unless a small fuel leak is affecting fuel pressure (which can trigger that code). If no fuel leak is seen/smelled, then check the evap hoses, purge valve, vent valve and canister. I made a cheap smoke tester that works great for finding vacuum leaks using one of the designs I found online. If you did a body lift, check the filler tube clamps.

So I did check the voltage and it was hitting 12+ volts. I ended up swapping the pump assembly and no more rough starts. Fuel pressure is now 51psi on startup. P0456 has not come back.

 

[BusterJeep]

So, here is the latest. Voltage tested at pump harness – 12.8 volts. Fuel pressure tested at pump connector – could not build up any measurable pressure. Tested purge valve – seems to work as expected. Inspected all the evap lines and didn’t see any issues. Came to the conclusion that the backflow prevention was not working in the fuel pump assembly.



Ended up putting in a new Delphi DFG1221 assembly as it was free due to the lifetime warranty from AutoZone. Since then, Jeep starts right up upon turning the key. Fuel pressure is 51psi upon startup. Drops to about 30psi after shutting the engine off. Pressure still above 10psi six hours later. Cold start 24 hours later, everything is the same. Pulled my tester and have driven about 100 city and highway miles since the pump swap. No issues. Definitely feels more responsive upon acceleration. P0456 was cleared as I had disconnected the neg battery cable while doing the pump swap. I did also put a new gascap on since I wanted to make sure that would not be an issue moving forward. So far, no more CEL lights have appeared. P0456 has not returned. No other CEL’s either.



I did end up cutting an access hole in the tub floor while the tank was on the ground. No more dropping the tank should I need to work on the pump in the future. For now, my toolbox covers the hole but someday I will fab up some type of cover that provides a little better seal for the hole.