Goldenfoot05

Hey fellow jeep nuts!

I have a 1999 Cherokee classic 4.0 auto. It is almost always hard to start. It acts like its flooded. If I crank it over without a foot on the pedal it takes 15 seconds or more to finally fire and when it does finally fire its not healthy, meaning it stumbles till it smooths to a nice idle. It runs perfect otherwise. Temperature doesnt seem to change the problem, it does it hot or cold though more so when its been run recently but even after sitting all night. Every so often after its sat for a day or more itll fire up nice and happy with hardly anymore than a bump of the starter. It will start quicker and run to idle quicker with the pedal to the floor.
I've been through the fuel pump, fuel filter, cleaned the injectors,
Changed the IAC, plugs, cap&rotor, wires and a bunch of other things I can't remember now. Fuel pressure is good though I feel I need to check it again because I can't remember if it holds pressure when it's turned off.

Anyone else come across this problem? Any ideas? I'm thinking of changing temp sensors next but I'm getting poor throwing parts at it. Thank you in advance!

CCKen

Sounds like you have leaking injector(s).

If it's okay after sitting for a length of time the fuel in the intake has evaporated and the rail has dropped to the point fuel is not being pushed past the injector(s). If it starts quicker and run ti idler quicker with the pedal to the metal, you are giving it more air to lean the mixture out (leaning the fuel in the intake/cylinders).

Do use a fuel pressure test gauge and see if the fuel pressure drops off rapidly after shutting the fuel pump off. If it is dropping to below 30 psi in less than 5 minutes, there is leaking fuel injectors or a check valve in the fuel pump module leaking. If you get a fancy fuel pressure test kit, there should be hoses and fittings you can rig up to pinch off the hose coming from the fuel pump to isolate it and/or pinch off the fuel injectors (rail) to isolate the fuel injectors.

Check to see if your oil level on the dipstick is rising, and see if the oil smells like gas. If so, stop what you are doing and replace the injectors before you ruin your engine.

Goldenfoot05

Thanks CCKen!

Checked the fuel pressure. Running its ~50PSI after I shut it off it drops to ~43PSI. Loses about 1LB per minute. It doesnt start easy at all anymore. Even after sitting a few days.

I wish it would trip a CEL.

Any more ideas?

MtnHermit

Those symptoms sound like a bad check valve in the fuel pump.

Easy to check, turn the key on several times, about 5-sec. That will run the fuel pump to build pressure. If it starts then its your fuel pump.

Either live with the above starting procedure of replace the fuel pump. I do the former.

Goldenfoot05

MtnHermit
Fuel pump/fuel sending unit is brand new. Mentioned the fuel pump and filter in original post. I suppose it's possible the replacement unit is bad from new, but I find that unlikely, losing 1 psi a minute isn't abnormal. My 93 bleeds down to 30 psi after sitting just an hour but still starts like a champ.
Keep the ideas coming.

Goldenfoot05

Going to end this thread with success!
Went to the scrap yard and pulled me a few injectors. I couldn't find any stock injectors so I did some research on the forum and my own based on what I could find at the scrap yard.
I wanted an easy direct swap in injector preferably with the 4 hole spray pattern and as close to stock flow as possible.
I found some injectors out of a dodge caravan with the 0-280-155-789 injectors. They are green. They flow at 21lbs/min are the right length and use the same connector as stock.
So far the hard starting issue is gone and idle and drivability are just fine. I will post more as I drive it more but so far they're a great fix for hard starting issues!
Thanks!
Helpful link. http://www.fuelinjector.citymaker.co...low_Rates.html

Muaddib420

Glad to hear! Nice job

Goldenfoot05

Little report. Still is running like it should and starts up better than ever! Notice a loss in the higher RPMs. Still nice and torquey in the low/mid range. Havent driven enough to report on mileage.
I will probably keep an eye out for higher flowing injectors to get the top end back.