96 Cherokee 4.0 country
It starts drives everything is great
When you let it sit and idle for more than a 5 mins or so it starts acting up. It loses power of you push the gas it misses/ shudders and then will die.
After it dies it won't restart right away have to let it sit for 5 mins or so and will start back up. When it starts the miss/ shudder/ no power is still there until you rev it up a few times. Then it is back to normal until it's left idle
I've replaced:
Fuel pump(just pump not unit)
Fuel filter
Plugs,wires,cap,rotor
Both O2 sensors
There are no codes stored in pcm
I'm don't want to just throw parts at it
If anyone had this problem let me know
Thanks in advance

 

Look for vacuum lines that are cracked, loose, or completely off. Check out your m.a.p sensor. Mine did this and it was the vacuum line going into the m.a.p sensor itself that had fallen off somehow. Plugged it back in and all was fine.

 

Fuel pressure and volume at the time of failure would be a good start. I know you changed it but new does not mean good. New means Never Ever Worked. Trust nothing. Watch for vacuum leaks and line issues to the MAP sensor. Check the ground strap right side of intake to firewall; should be 10mm bolt on both ends...known to corrode and loosen up. Monitor the TPS at the throttle body. 3 wire sensor; 1 is 5 volts, one is ground and one will be return voltage back to PCM. Low signal at idle; typically .6-.9 of volt and increase steady as you open the throttle. a lab scope is really needed to watch; if you have a DVOM in glitch mode it may catch something. Find the crank sensor, back left corner, top of the trans bell housing area. Can you wiggle a long extension down to the top of it? GENTLY tap it while the engine is running. If it falters, change it. Crank Sensors are affected by hot and cold when they go bad.

 

Thanks man I'll check into all of it and get back

 

2 add'l thoughts- because of the age how does a fuel sample look? Easy way is use a clear container when doing a volume test- should fill a Snapple bottle in approx. 25 seconds. And while there look at the color of the fuel, clean? Good, Particles and debris? Not so good. And last when I say 10MM bolt I mean the head not the thread. That ground strap off the back of the intake is a main system ground and wreaks all kinds of havoc at times. It is usually a wide braided strap. Good Luck.

 

Actually it's not the main system ground. The main battery (-) to chassis ground is at the right inner fender (G101), and at one of the ignition coil attach studs (G102).


The braided cable you refer to is only there for radio noise suppression. If G101 is compromised the bonding strap is forced in to taking the chassis ground load.

 

Thanks for the pic. That is the strap I was referring too. But I can tell you from multiple experiences clean connections at that strap have solved more than a few strange problems over the years. But yes, you are right in its design and intention.

 

Note what I said about the battery to the right inner fender being corroded and forcing the bonding strap to take the chassis ground load.


I've also read accounts of replacing/cleaning the bonding strap connections and fixing problems, but no mention in those accounts of repairing the battery to fender connection.

 

I will have to take note the next time I run across it. Usually I clean batter cable, connections, etc FIRST as a matter of habit. That ground inspection and repair if needed is after the fact. So I can't say that cleaning them both gave the impression it was at the intake or not. From memory it was always cleaning the intake strap that solved the issue BUT the t5heory doesn't necessarily support that .