I have a 2010 and sometime when I go to start the jeep it’ll bump for a split second but won’t turn the motor all the way over. It’ll do that a couple times and then fire right up. Sometimes it will just continue to bump and not start. Has new starter, relay, ignition switch and pigtail, I have cleaned the battery posts and it’s still doing it. I’m at a stand still. Any help is appreciated.

 

Check the main ground wire between the battery and the engine block. There may be some corrosion somewhere, causing high resistance. It could even be in the wire itself. The wire may show zero ohms to the block, but the problem may manifest itself under load.

The starter is grounded through its metal housing to the engine block, so there is no dedicated ground wire that goes from the starter all the way back to the battery. A way to test for high resistance is to put a voltmeter negative lead on the negative terminal of the battery and the positive lead on the metal housing on the starter. Then try to start the engine. You should not see any voltage, or at least it should be no more than about 0.5vdc. If it's any more than that, you have a ground issue.