Hey guys, quick question for ya's.
Soo, I recently picked up a 87 cherokee cheif, 4.0L 5spd. And ever since i got it, its been hard to start... Like it will crank and crank and crank and crank, but if i hold my foot to the floor, it will fire. but when it does start it runs rich and misfires for a few seconds, but then other times, I can turn the key and it will turn over 2-3 times then fire off, but still run a bit rich for a few seconds and miss for a bit. Could this be dirty injectors? we were also looking underneath and noticed the PO put on a new fuel filter, and it looks to be on backwards? they also didnt even put it into its holder, just left it hanging there.. with the old filter still in its mount. [lazyness I guess?] Any help would be appreciated!

Oh! and sometimes at a cold-start up if its kind of chilly out the engine knocks for about 2 seconds... is this something i should worry about? or is it a older jeep thing?... It only does it about once every 2 weeks..

 

What brand of oil filter? 4.0s are picky and must have high quality oil filters because of the mounting position.

Get the fuel filter issue addressed ASAP.

Since this is a Renix Jeep, you need to click on the "pink link" in my signature and perform the procedures outlined in posts 1 through 5. No shortcuts. This will save you headaches in the long run.

A complete tuneup including NGK plugs, wires and cap and rotor with brass terminals.

Clean the throttle body:

Courtesy of TJWalker:

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The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

"Gently" wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled



Make sure the vacuum harnesses on the engine are in good shape and routed properly. The one from the throttle body to MAP sensor is critical and if leaky, can cause the exact symptoms you are describing.

 

Thanks for the info! I'll have to try this when i get home. I'm currently working away and dont have my tools with me, and I'm too far away from a parts store if anything breaks lol