Recently purchased a 2001 Grand Cherokee Laredo 4.0, love it WHEN its running right.
Ran great when we bought it, (it had been sitting for 2 months), went to town to pick up pizza and it started cutting out, engine light started flashing and it wouldn't shift gears out of second. Limped it home...Saturday morning we decided that maybe sitting that long something gummed up. We changed spark plugs, oil, air filter, fuel filter, put lucas in the transmission and gas tank. It ran great for that tank of gas.
Next tank of gas. It starts doing the same thing. I go to town with it cold it runs fine, run in the store for a minute, come out and it starts fine. Take off and get to second and it starts cutting out and wont shift to third. Limp it home again.
We have since replaced the coil rail, cam position sensor, crank position sensor, output speed sensor...reset the computer, and its still doing the same thing.
Runs fine when you take off and its cold then goes to crap. Any ideas I have not tried. PLEASE help
The only codes it has thrown are 300..301,302,303,304,305,306

 

hmm... those codes translate to random misfire on all cylinders.. so its probably a bad fuel pump/regulator or even bad pcm since it controls injector pulse

 

Is there a way to test the pcm? We thought about the fuel pump being stopped up or something: still have a half a tank of gas and kinda waiting to pull that. lol Thank you for your hlep

 

Just for grins, throw a couple of cans of drygas into it and see if it makes a difference. Could be water in the fuel.

 

The misfire seems to be fixed under normal conditions. The problem now seems to be the transmission. Still can't get it to shift past second once it warms up. Changed the fluid and filter this morning and still doing the same thing. If you push the rpm's in second you can get the misfire to show in the codes.

Any ideas on the tranny?

 

Sorry, not me.

 

Ok. We added a ground wire and adjusted the kickdown cable left it off the battery all night....this morning runs and shifts perfect.

Not sure what fixed it but want to thank all you guys for your help. We have turned this forum upside down reading posts and trying everything. You have all been a great help. Thank you