1992 jeep cherokee 4.0 engine. After driving for 5 minutes the fuel pump starts getting real loud and then the engine starts running rough. When I first crank the engine, the rail fuel oressure is 31 psi and then I remove the vacuum line from the fuel pres. regulator the pressure goes up to 39 psi which is all normal. After 5 minutes of driving the pump gets real loud and the engine starts running real rough and continues to get worse. The rail pressure at this time is falling to 15 to 10 psi. After it sits for a while all is good for another 5 minutes and then it all happens again. What's the problem.

 

check for leaks down the fuel lines

sounds like a bad fuel pump.


how many miles are it? if its over 150k, its not a bad idea to get a new one anyway.

 

This could be caused by a clogged fuel pickup screen. When small particles and stuff build up in your tank, it will wind up on the pickup screen, and when you shut it off, it all falls off of the screen, only to be picked up again when you start it up again. Loud noise = pump trying harder to maintain pressure.

Aslo, could be as stated before, that the pump is going bad, and cannot keep up for very long. Typically if its a leak, it will be constantly the same loss of pressure, not gradual.

Just my 2 cents...

E

 

Bad fuel pump.