Installed a 4.0 in my 89 yj from a 99 grand cherokee. Have inline fuel pump and return filter with 55lbs pressure. About 6 to 7 miles down the road start losing fuel pressure. Only at 75 degrees and up, outside temp. When its cooler it runs great. Like at night riding. Motor temp is 200. Fuel pressure starts to drop to 40, 30, 20, 10. If I let the motor cool down it runs fine again. Replaced the pump 3 times, still does the same thing. Fuel pump is mounted outside the frame towards the back. Fuel rail is pretty hot. Have pressure gage hook up all the time to monitor pressure. I can releave pressure and a lot of air comes out with fuel. Weather great, need to fix this. Also have electric fan with stock fan with shroud. Help
05-03-2012 10:38 AM
I was having common issue and turned out to be dirty crank position sensor. Removed cleaned it up and issue cleared up. Something to check. Only happened after jeep heated up under load.
05-03-2012 01:08 PM
Thanks Tom. Already tried that and didn't work. Have a friend with same problem and it didn't help him either.