91 XJ I need mechanical assistance

[BAMbam90]

Good morning guys, I recently picked up a 1991 jeep Cherokee Laredo automatic with 4.0. When I purchased it the previous owner informed me that it needed a fuel pump. when you go to start the jeep it spits and sputters and usually will not start unless your prime or turn the key on and off 3 or 4 times. Once the fuel pump is primed it fires right up with no issue. I replaced the fuel pump, fuel filter, and fuel pressure regulator and still do not have the issue fixed. If I prime it the jeep will start. If I just hop in and turn the key to go it will spit and sputter and will not start.

I am above my mechanical ability at this point and could use any ideas or assistance trouble shooting the issue.

 

[Mekcanix]

check the ballast resistor on the fire wall around the brake booster or the air cleaner mounted to the fender I had mine fail on the way home one dark and stormy night and it sounds suspiciously like your issue


pic id from a forum and the what is this is the resistor its made of ceramic and if its gone it acts like a dead fuel pump easy way to test is to bypass it and connect the 2 wires but dont leave it that way or you will burn out pump. As I understand when you start a XJ it runs the pump on 12 v then once it sees a run signal it switches to 6 v through this resistor and if the resistor is bad it acts like the fuel pump is bad

 

[BAMbam90]

I PULLED BOTH WIRES AND USED A PIECE OF BARE WIRE TO LINK THE TWO TO SEE IF THAT WAS THE ISSUE, IS THERE ANOTHER WAY TO TEST THE RESISTER OTHER THAN JUST REPLACING IT?

 

[Mekcanix]

if you jumped it out and it made no difference then there is another issue.
and with out being there to actually look and test I am useless to you sorry

 

[BAMbam90]

THANK YOU FOR YOUR TIME AND INFORMATION, IT IS GREATLY APPRECIATED!

 

[adventure_is_necessary]

Are you just priming by having the key on and letting the pump kick on? I believe it is common for the some fuel to return to the tank, but not 100%, which is what it sounds like is happening. Somehow you're getting air in the fuel lines, and with replacing the fuel pump, I can assume the new gasket sealed up just fine around the pump, so either you have a leaky/sticky injector, bad check valve, or leaky vacuum line. Easiest way to test for that is to test the fuel pressure. I believe around 50psi is standard. lower than that means you've got a leak somewhere in the fuel system. I've never used a gauge to test a fuel systems pressure, but the symptoms I have seen before. Hope this helps!

 

[American Off-Road Club]

The ballast resistor cuts the voltage down to the fuel pump once the engine is running more or less to make it quieter. As for your issue, you have either a stuck injector (open) or potentially a bad ground to the pump which is limiting the response of the pump to the ignition. The ground in that harness is actually on the driver's side behind the interior panel in the back hatch area. If you are going to replace the injectors, do yourself a favor and get a set of 4 port injectors, and no not from a mustang. Feel free to PM me.

 

[Nmxj89]

Good morning guys, I recently picked up a 1991 jeep Cherokee Laredo automatic with 4.0. When I purchased it the previous owner informed me that it needed a fuel pump. when you go to start the jeep it spits and sputters and usually will not start unless your prime or turn the key on and off 3 or 4 times. Once the fuel pump is primed it fires right up with no issue. I replaced the fuel pump, fuel filter, and fuel pressure regulator and still do not have the issue fixed. If I prime it the jeep will start. If I just hop in and turn the key to go it will spit and sputter and will not start.

I am above my mechanical ability at this point and could use any ideas or assistance trouble shooting the issue.

Cranks shaft position sensor!