fishbone

Got a 2002 Grand Cherokee, 4.0L, with an extended crank time before start. Once started it runs fine, no performance issues. I checked fuel pressure, in the morning and it read zero. Key on engine off, pressure just ticks about 5 lbs and not steady, while cranking fuel pressure builds, vehicle starts and pressure reaches a steady 55 lbs. As mentioned, while running there are no issues. With pressure gauge still attached, turn off the vehicle and the pressure instantly drops to zero. Fuel is getting dumped back to the tank immediately. Now with all that said, I have recently replaced the fuel pump, about 2 months ago, everything was fine after the install. Replacement pump I use was a Delphi, it came recommended highly and cost a bit more. So, my question is what else can this be besides the pump module? I really hate the thoughts of having to drop the tank yet again and deal with Rock Auto or Delphi for some compensation or a replacement pump. There is no fuel smell or fuel leaks and because of how well it runs once started, I am inclined to believe that it is not the injectors. This model does not have an external regulator, unless I missed it somewhere. Any ideas would be helpful. I have never seen pressure drop to zero instantly. I realize when a pump is going bad there is some bleed off but, it's usually slower and leaves a bit of residual pressure at the rail.

dave1123

On the WJ, the pressure regulator is part of the filter, which is external. You probably didn't need the pump. In the start cycle, the pump only runs momentarily to pressurize the system. When the PCM gets a signal that the engine has started, the pump runs continuously. On some engines, it's alternator output that triggers the PCM. IDK what it is on jeep's system. It may be the CPS signal.

fishbone

First and foremost Dave, thank you for the reply. I know I can always count on you for some good jeep tech advice. Yes, I did need to replace the pump. It was extremely noisy and barely able to keep 30lbs of pressure while running so, I believe the pump replacement was the correct thing to do. What I took out of there was what I believe to be the original chrysler/bosch pump with 145,000 miles on it. As for the filter, when I replaced the pump, I also replaced the filter. I used a Hastings filter. So, I do have a new pump and filter. I was not aware that the filter was used for pressure regulation. Perhaps I'll take a look there first before pulling down the tank. Maybe the filter I got was not up to the task of handling the 50 plus lbs. of pressure that this new pump is putting out. Thanks again Dave.

dave1123

There is one other thing that might be involved. When you dropped the tank, you may have stirred up some sediment that plugged the regulator's port and valve.

Here's a story about a similar situation with my Dodge Caravan. The filler pipe rotted out, allowing road grit to enter the tank. I replaced it with a homemade pipe because of the cost on a new one. I started having problems with fuel pressure within a week and because of time, I took it to Dodge for replacement. That pump failed in 2 weeks, so I took it back and they replaced it. I asked them if they cleaned out the tank like I'd asked and they said no but they did the second time. Really? that pump lasted 2 months before starting to give me problems AGAIN! I sold the van to someone else who I made aware of my problems. That's when I bought my ZJ.

fishbone

I did try a new filter as research indicated failure of certain brands shortly after installation. I put on a Wix this time but that did not solve my problem. I suppose I will have to drop the tank again and take a look at the pump module. I guess new doesnt mean good. Thanks for the info on cleaning the tank. I did do a thorough cleaning when I replaced the pump originally.