Jerms
NAXJA Forum User
- Location
- Northern utah
I really need some help figuring out this problem with my xj, before we get into the details of whats wrogn heres what you need.
88' XJ 4.0 aw4 auto np242.
The problem is that the fuel system seems to be loosing its prime. We just recently replace the fuel pump when it just died driving down the road. The new fuel pup worked great for a while, but then a few weeks ago this issue started where you could start the engine and it would immidatley die but would restart just fine. the problem has progressivley gotten worse to the point now where you may have to crank the engine while it it firing on one or two cylinders for up to 3 minutes before it gets full fuel preasure and turns over. I suspected that the fuel check valve on the new pump was bad so i bought another brand new pump from a different store (New pump is a bosche) and installed it. that had absolutly no effect on the problem infact i would say that it even made it worse.
So in trying to track down the problem i did some looking over of the electrical diagrams and discovered that it is possible to run the pump with out cranking the motor by unplugging the green wire from the starter relay and then holding the ignition in the start posiotion. Works great for running the pump and trying to prime the system but when you do this an interesting thing happens you can hear the pump running but it sounds like it is running on about half speed but then there is a dull "thunk" kinda noise and pump kicks in all the way and jeep will trun right over like normal after that. Now it is also interesting to note that when you are trying to "prime" the engine and the pump sounds like it isn't runnng at full speed there is no fuel preassure meassured at the test port. I should also note that there is no problem once the engine is running it runs fine.
Other things that i have tried:
3 fuel pumps.
2 fuel pump relays
Direct wiring to the pump connector at the tank.
I have also tried pinching off the fuel return line at the tanks to see if the fuel preasure regulator was not functioning.
Any help that you guys can provided it greatly appreciated.
Jerms
88' XJ 4.0 aw4 auto np242.
The problem is that the fuel system seems to be loosing its prime. We just recently replace the fuel pump when it just died driving down the road. The new fuel pup worked great for a while, but then a few weeks ago this issue started where you could start the engine and it would immidatley die but would restart just fine. the problem has progressivley gotten worse to the point now where you may have to crank the engine while it it firing on one or two cylinders for up to 3 minutes before it gets full fuel preasure and turns over. I suspected that the fuel check valve on the new pump was bad so i bought another brand new pump from a different store (New pump is a bosche) and installed it. that had absolutly no effect on the problem infact i would say that it even made it worse.
So in trying to track down the problem i did some looking over of the electrical diagrams and discovered that it is possible to run the pump with out cranking the motor by unplugging the green wire from the starter relay and then holding the ignition in the start posiotion. Works great for running the pump and trying to prime the system but when you do this an interesting thing happens you can hear the pump running but it sounds like it is running on about half speed but then there is a dull "thunk" kinda noise and pump kicks in all the way and jeep will trun right over like normal after that. Now it is also interesting to note that when you are trying to "prime" the engine and the pump sounds like it isn't runnng at full speed there is no fuel preassure meassured at the test port. I should also note that there is no problem once the engine is running it runs fine.
Other things that i have tried:
3 fuel pumps.
2 fuel pump relays
Direct wiring to the pump connector at the tank.
I have also tried pinching off the fuel return line at the tanks to see if the fuel preasure regulator was not functioning.
Any help that you guys can provided it greatly appreciated.
Jerms
