I am currently having a hard time chasing down a problem when it comes to starting my Cherokee up. When I attempt to start it up, I crank the engine over a good 6 seconds before it catches with the input of the gas pedal being pressed down. Once the engine does catch, it has a short stumble before the idle evens out and runs smoothly. This usually happens in the mornings and after the jeep has warmed up and sits for a couple of minutes.

I have replaced and cleaned numerous parts trying to chase the issue down. Fuel pump has been replaced with a new one, upgraded stock injectors to 4 hole, new crank position sensor, cleaned out the throttle body yesterday along with all sensors removed and cleaned, new cap and rotor along with spark plugs (which were gaped correctly) and wire set. I reset the computer twice since I installed the fuel injectors and fuel pump and it doesn't seem to do anything......I need some help with this!!!! Only thing I can think of left that I haven't checked is the cam position sensor.

 

Fuel Pressure Regulator. Might be allowing your rail to lose pressure after it sits. Turn the key off and on several times (don't attempt to start). You're just looking for the fuel pump to come on and prime the rail a few times. Then try and start.

Another way to check is to unscrew the cap on the schrader valve on your fuel rail. Press your key on the valve and see if fuel squirts out after it's been sitting. If no pressure, it won't squirt.

Just dont catch the motor or yourself on fire during the process.

 

Could be a lot of things. What i'd do is cut the problem in half and conclusively determine if its a fuel issue or not.

Hook up a fuel pressure leakage test system which can isolate fuel leakage problems to either the 'pump/regulator/check valve' or injector leakage.
If its a fuel issue it'll:
1. verify fuel pressure is in/out of spec.
2. if its rapidly loosing pressure after engine shut off it can isolate to either injectors or pump system.

That test would verify a bad or good fuel delivery issue.

 

I ran this test when the OEM pump failed and the pressure would fall in a couple of seconds. I do have doubts of the new 4 hole injectors leaking for some reason. I do find it odd as when I'm cranking the engine over, as soon as give the pedal a push, it catches, stumbles for a second and stays running fine......

 

I did the screwdriver method checking with the schrader valve......I left the truck sitting for a good hour and checked the valve and there was plenty of pressure in the line! gas shot out as if pressure didn't drop??? I'll try this little test again right now.

 

Did you run that test with a fuel pressure leakage test system?
They have valves to isolate either a leakage in the injectors or the pump system.

 

I ran a fuel pressure test with a kit from my local Autozone. This was done with the OEM pump installed and was replaced due to the gauge not holding pressure.

I still haven't gotten around to troubleshooting the problem any further. I've been busy moving things around. Hopefully I have a chance this weekday or weekend to work on it some more. I'll give another update when work is done