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4.0 wont start. Need help!!!

#1
Well i finally got everything back together after changing my exhaust manifold. went to start it and it would only crank but not turn over. Similar as if it wasn't getting fuel or spark. Checked pressure on the fuel rail (via the schrader valve) and sprayed fuel so seems ok. Haven't checked spark but it has a new coil less then 6 months old. It has all the symptoms of a bad crank position sensor but that was also replaced within the past 6 months.

Any ideas? Thought about trying another cps but they are a little pricey considering im not positive thats the problem.
 
#4
but on a serious note, theres only 3 things it needs right? spark, fuel, and compression. I'm assuming you have compression and you said you have fuel, so check for spark
 
#5
hahaha dont worry, chromos are currently in the mail as we speak. no more 30 yr old stockers for me.

but yes it has compression, checked that a few months ago when it was running funny. Fuel it seems to be getting cause the rail has pressure. Didn't have time to check spark before the rain came in last night. So hopefully ill check that today when i get off. but it has new cap, new rotor button, and new coil. and i doubt all my spark plugs are bad at once if it was running fine before.

What would tell the computer to not send spark? Bad CPS should but its new. What else?

And yes meaders, hydrausalator valve is in good working shape. that was the first thing i checked. Wondering if it could be the rotary girter?
 
#6
hahaha dont worry, chromos are currently in the mail as we speak. no more 30 yr old stockers for me.

but yes it has compression, checked that a few months ago when it was running funny. Fuel it seems to be getting cause the rail has pressure. Didn't have time to check spark before the rain came in last night. So hopefully ill check that today when i get off. but it has new cap, new rotor button, and new coil. and i doubt all my spark plugs are bad at once if it was running fine before.

What would tell the computer to not send spark? Bad CPS should but its new. What else?

And yes meaders, hydrausalator valve is in good working shape. that was the first thing i checked. Wondering if it could be the rotary girter?
what all did you change when you took the intake and exhaust off, i'm guessing there may be something not hooked up
 
#9
I pulled all the necessary pieces off to change the exhaust manifold. Labeled all vacuum lines and sensor plugs. Put it all back to where it was suppose to be. Double checked and couldn't find anything not hooked up. I'm stumped. I just want to drive my jeep again.
 
#14
Yours is new enough that you will have PCM controlled ignition and fuel. The fact that there is pressure means nothing if the PCM is not opening injectors. Spark is the same way. You need to take the time and test all components in the proper order to truly find out where the problem is. You need a FSM, Haynes manual to perform the troubleshooting.
Sensors, senders, ect..... can fail overnight. Just because it was new a month ago means nothing. I have replaced sensors, and had them fail within 24hr of the install.
 
#18
It did throw a check engine light, but i dont have a scanner to check what it is. I may "try out" a new cps and see what it does.

Correct Tucker, it turns over fine with the starter so no batter issues but it just wont fire off and run on its own.
 
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