I got a 90 4.0 and it take me a while to start it. Then when it starts it shuts off. I start it again and again until it stays on. When i drive it feels like no gas is getting through, I can floor it and thing will barely move, but sometimes it runs like new. I m confused on what to replace...

 

its a common problem on the 4.0's. try replacing your Crankshaft Position Sensor. your sensor gives signal to your pcm and then distributes that signal throughout the motor. good luck and let me know how it goes.

 

Before you replace, first check. Check for a spark while cranking to see if you have normal spark plug firing or an ignition problem. Check fuel pressure to see if you have normal fuel pressure or a fuel issue. Then you can troubleshoot the problem.