I have a 1988 4.0 Cherokee.. Only starts first thing in the morning. For awhile I could get it to start after warmed up by holding the pedal to the floor. Now it will only turn over the rest of the day. I've done new plugs, TPS, vacuum lines, fuel pump and starter. I cleaned the idle air control mod and throttle body. Any ideas on what it could be. She's old but still solid with great 4x4. I'd like to keep her for my kid to use.

 

Just brainstorming here but I would absolutely test the coolant temperature sensor, the one that provides input signals on coolant temperature to the computer.

If that sensor has gone south, the computer doesn't know how to calculate proper fuel/air ratio which can result in hard or no starts when the engine is warm. I've actually seen and resolved this a couple of times on the 4.0 engine.

Cruiser54 will likely chime in with more ideas as he is the Renix guru here.

 

I forgot to put that in... I did the temp sensor. Its a two wire on the bottom of the engine on the drivers side. I didn't see another one. I've been told they have two but no idea where it could be. This model do not have one on the thermostat housing. And I had changed the system from that problematic pressure bottle to a normal system with an over flow.

 

Have you tested the CPS ? worth a look see.

You have a temp sender for gauge on top rear drivers side head. You have an IAT ,intake air temp, on manifold in front of throttle body.

 

this happened to me recently, turns out it was the IAC. I thought cleaning it would help but turns out t was completely nonfunctioning. Test it out and see