@ CCKen
"If the coil rail tests good, I would seriously consider the Crankshaft Position Sensor is suffering thermal failure.

Use only an OEM CPS. Aftermarket CPS' have a habit of failing right out of the box.


Coil rail is good so I think my last stop would be CPS. now I hooked up the OBDII to test the "Live data", this should show me the RPM right? but the OBD says no connection. Does it mean CPS is not giving any signal, therefore its messed up?



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By the way, the "check engine light" went "on" and checked what's causing the light. the OBD indicated P0100, Generic MAF or VAF,A circuit malfunction". knowing that XJ, 4.0 2000 doesn't have MAF or VAF, what could it be?
Thanks for the input guys.

 

Sounds like the scanner you're using is not set up for a Jeep.


My scanner has a feature where I can plug in the data for any vehicle, which I do for my 2000 T&C and the wife's 2013 T&C. Obviously my '99 XJ is programmed in.


You must have the correct connector for your DLC and the scanner must be compatible with the XJ Jeep. Could be the reason you are not seeing connection/RPM in your live data.

 

So Guys I am back.
I seek the help of a mechanic to replace the CPS but he advised me not to since its starting and running, claiming that if CPS is messed up, it wouldn't even start up. checked my hoses again and found out that the hose that is connected to the intake manifold connection for "Leak detection Pump is loose so I refitted it,any ways, So I drove around for a 10 miles, it was find but I am not satisfied with the way engine is running. I reboot/reset the PCM(?) buy switching on, head light on/off then switch off. after around five miles the engine runs better now. I drive randomly from 10 to 35 miles each, just to test its performance and so far no Hiccups, I now have a total of 165 miles and running good.
Makes me confident that its good to go. Any input Bros. I hope this is it. I want to put a closure on this thread and Thank you to those who helped in one way or another.
PS: CC Ken, You talked of compatibility, I bought a highly recommended product by forum members. this helped too.