Ok so, I have a 2001 Jeep Cherokee 4.0L. For over a year now I have had an issue with it starting hard. I thought it was the check valve in the fuel pump, and have put fuel pumps in it so far with this making no difference. My other thoughts are a leaky injector or heat soak both of which I know are fairly common. But here is the interresting part, it only does it when warm. If it is 50 degrees outside and I go out in the morning it will crank and crank and crank and start. If I have just driven it, it will start hard. But when it 20 degrees outside, starts great! Is heat soak so big of a problem that just the air temperature would affect it? Is there something I am missing? It is not causing any problems it is just embarrassing when I go to give a friends a ride and they wonder what is wrong with my jeep 😝. -AJ

 

You may have a sticky injector that hangs up and doesn't close tightly when warm. This will fill a cylinder with fuel and causes a misfire when starting after sitting for a short time, delayed start in the morning, and sometimes starting normally. For the first cold start, try turning the key on and off several times for a few seconds each time before starting and see if it starts better. This gives the fuel pump more than one shot to pressurize the fuel rail. Mine is basically doing the same thing and I find it will start better when hot if I let it sit until the temp comes down a bit before starting it. If it runs rough when restarting it, I shut it off, wait a minute or two, and restart. Sometimes that works, sometimes not. The original Sieman's injectors are junk. It's getting a set of Bosch 4-holers at my earliest convenience.

 

Ok, I will try cycling the key before starting it. I also could check the fuel pressure to see if it is dropping after I turn the key off right? I will do some more experimentation.

 

Good idea...and although the suspect cylinder could be any of them... check the one in the middle of the rail. I've read lots of people having heating issues on that specific injector due to no protection from the factory in that location.