Ok, i just finished fixing my last problem and now a new one has come up i have a 96 xj 4.0 4x4 things that have been replaced:

Coil
Wires
Plugs
Distrib Cap
Rotor
Fuel Pump
Fuel Filter
Ignition Lock
Radiator
Both Hoses
Water Pump
Thermostat
Clutch Fan
Aux. Fan
Powerstearing Pump
Transmition coolant lines
Oil Filter
Tran. Filter
All U-Joints
3" Rusty's Lift

after replacing all of this i was hoping that i wouldnt "have" to work on my jeep anymore... well i was wrong. Usually it will start right up, sometimes i will have to crank it while holding the gas in and it will start after a couple cranks. Sometimes it will start and sound like its ready to die, but keep choking through it and then after about 10 seconds it will go to a normal idle. What really makes me mad is it will start up and drive, making me think everything is going to be ok then the engine dies. It is just like i turned the key off it does not spit or spudder most of the time i cant even tell the engine shut off till i see the GEN light come on and realize there is no power. When this happens to get it to start i have to hold the gas in while cranking and it will keep running as long as im holding in the gas. As soon as i let off the gas to go it dies again, no sputter just shuts off.

I have done a compression test on the head and it is good, the only thing i can think of is when we replaced the fuel pump the wire that connects the pump assembly to the fuel pump had shorted out so we cut off the short and put new ends on the wire ect and put it back together. Im waiting for the weekend to check out the pump and was going to put a fule pressure gage in so i could watch that. And i was reading about testing the crank position sensor. I was just wondering if anyone could think of what else to check. I really love my jeep but every time i fix 1 thing and hope i can finally rely on my jeep something else brakes and im stranded 30 min away from my house. Thanks in advance for any help.

Will

 

Check your IAC for gunk and clean it

 

I had the same exact problem happen today at school. Im thinking it might be the idle gauge? I just drove home with both feet and its a pain in the ***.

 

What is IAC?

 

1. Clean your throttle body and idle air control. They get carboned up. More below.

2. Test your "throttle position sensor". Located on the throttle body. Not expensive to replace if necessary. Having to "tip in the throttle" to keep the engine running can absolutely be a bad TPS.

Both of the above can create the symptoms you describe and should be ruled out before looking elsewhere.

Start with #1 and if that doesn't resolve, move to #2. Be methodical. This is a process of elimination.
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The Idle Air Control (IAC) is mounted on the back of the throttle body. 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

Reinstall IAC and check idle quality

 

When mine was doing that. I knew it was the crankshaft positioning sensor so I replaced it then still had the same problem. I was stumped. Come to find out the aftermarket sensor's electrical connector wasn't getting good connection. Easy fix just have to bend the tabs just a little so they get good connection. Just want to mention this to everyone so you don't get stump like I did.

 

Thanks for all the info everyone!! I wont be able to get to test anything out till this weekend, but if anyone has anymore ideas keep'em coming!!! I am new to working on vehicles but to me it seems like it could be getting to much fuel when it is running rough, and when it stalls and starts it really stinks, like i said im new so i could be completely off on this but thought i would throw it out there. Is that kind of what the IAC helps with is the air/fuel mixture? What about when it just cuts out w/o any spitts or sputters while im driving?

 

The long post above describes the operation of the IAC and how to remove/ clean it

 

Could very well be the crank sensor. Changed mine out last summer.

 

I had the same problem with my xj..it continued to get worse real quick and I couldn't figure out what was wrong. Come to find out there was only 21psi at the fuel rail... the pump I just put in about 6 months ago was faulty... check your fuel pressure, your pump could be bad too!

 

I just replaced my TPS also. Someone told me it was called a TPU? I really need to get a manual on these jeeps.

 

Question about checking sensors. If my jeep only "fails" sporadically and i hook up an ome meter to the sensor will it always read bad or will the jeep have to fail to get the bad reading?

Also would it be worth it if I whent to the junkyard and offered like 5$ for a sensor and try it out?

 

I don't know if the '96's have CPS's but that will definatley cause a no start problem. It's located at the back of the engine on the bellhousing. They just kinda fail without notice and the symptoms get worse. A few other ideas might be tesing the fuel pressure, and testing sensors such as IAC and TPS. Also check for vacuum leaks, Mine kept dying and was running like crap and I would have to keep my foot on the gas, turned out to be fuel pressure was wrong due to incorrect vacuum at the fuel regulator. hope this helps, just some ideas. Godd luck!

 

Changed out my CPS, not the problem. just FYI for anyone looking to do this, you seriously need like 2-3' woth of extension w/ swivle head. and undoing the rear driveshaft might help but i dont think it would be worth the hassle. Its just 2 bolts and it comes right off but anyway.. that did not fix my problem.

thing that really makes me mad guy at autozone said if i change it and it didnt fix it i could bring it back but i only had a couple hours... well i changed it and of course it drove fine past the time i could take it back, and all weekend till im on my way to work I dont get stranded i just have to drive w/ my foot on the gas at all times. seriously once it happens if i let my foot off the gas the engine cuts out. but i can start the jeep and let it idle for ever and has no problems besides sometimes idling rough for about 10-30 seconds when it first starts then idles perfectly fine. could it be something with my fule system? I am looking for a gage to run up to my dash so i can watch it since it only does it when im driving. Is the little threded peice comeing out of the fule rail where i would screw the gage to?

 

Once again sounds like a fuel pump to me