I picked this 1991 Cherokee up at an auction and it ran pretty good at first but now it pops on acceleration and has no power. I did a fuel pressure test and it was low (15 pounds) and the leak down was almost instant. I was thinking the hose from the pump to the metal hose in the tank could have a leak. Could a bad pump cause a leak down like this ? all the injectors have been cleaned and tested good.

 

Time for a new pump assembly. Bosch brand only if you want it to last.

 

Start with replacing your fuel pump. Then do more testing. Bosch is my first choice, Carter my second. Don't install an Airtex or anything rebranded by Airtex unless you like doing things twice. SEARCH to find out why.

You need approximately 31 psi at idle for your 91 4.0 engine. Then disconnect the vacuum line leading to the fuel pressure regulator and the pressure should jump up to about 39 psi. Check the condition of the vacuum line leading to the regulator and also if there is any fuel in that line, that is indicative of a ruptured diaphragm in the regulator.

Good luck and keep us updated!

 

Replaced the fuel pump and it runs like a 26 year old jeep . it runs pretty dang good. Wasnt the pump so much as it was all the rubber parts turned to goo fuel line included. It sat up with a 1/2 tank of gas for over a year so not surprised. On to the next thing (brakes)