Cherokee CUT IT OUT!!!

I need help before I pull the rest of my hair out. I have a 1990 Jeep Cherokee, 4x4, 4.0 straight line 6. It has 274,000 miles on the odometer. I put an engine in three years ago it had 34,000 on it. It has ran like a champ until about 4 months ago. I do not have alot of money to pay new parts so I have tested and replaced very cheaply.

My problem, when I'm driving, and it seems to be at about 2,000 rpm, it cuts out. Its like its running out of gas. However, it does not do it all the time, I would say it does it about 80% of the time. When I give it gas from a stop sign and go, it will cut out around the same rpms. It will only do that 50% of the time. when going down the highway it only does it when I keep the pedal steady when I'm cruising at 65. I can give it more gas and it stops but once i keep it steady it starts choking.

Here is what I have done with new parts, spark plugs, air filter, fuel filter. None have helped. I have several used parts and I put those on to see if it helped, they didn't. A used fuel pump, fuel regulator, distributor, cap and rotor, and O2 sensor. None changed a thing.

I have pulled the throttle body and cleaned it till I could almost see my self. I pull the fuel rail and put card board under and turned the key on, none of the injectors leak. Also had the wife turn the key over, all injectors work.

I have spent alot of hours read on here about problems close to mine, but everything I try doesn't help. So any one with any ideas would be great. Thanks for your help

Im not an expert on Cherokees, especially when it comes to the 4.0 but I have spent a lot of hours on the Jeep forums myself, and based on that I would say:

Do some research on the crankshaft position sensor, as well as the fuel pump ballast resistor, both are located under the hood somewhere haha, and Ive read things about both where people have had similar problems.

Hope that might at least point you in a direction.

Classic CPS (Crankshaft Position Sensor) issues...I bet they've been getting slowly but steadily worse?

If the CPS doesn't cure your issue 100%, then it could be the TPS (Throttle Position Sensor). But I'd go with the CPS first.

Thank you for your replies. I will try the CPS. To make sure I'm on the same page its the sensor on the left side on top of the bell houseing right? I had to replace the throttle positioning sensor two years ago. So hopefully this is it. I will keep you all posted and post if it does fix the problem. Thank again

Yep, as you're facing forward it's at the 11 o'clock position. I used long extensions to reach it, lying underneath near the transmission. It's a bit of a bear to reach, but on mine it was only 1 bolt + electrical connection.

Well, after a busted knuckle and some bad words the CPS is IN!!! BUT, it did not fix my problem. Took it down the highway and at a steady 65 it started choking again. I brought it back to the house and decided to check the flywheel to look for cracks. Did not see any. I have replaced flywheels in the past in a 94 cherokee, and commanche because they had cracks. But nothing on this cherokee's flywheel. So should I replace the TPS?? When I replaced the first time it would not shift at all, and when I replaced it worked like a champ. So could it cause a new issue?? Also, I forgot to mention that I swapped the MAP sensor and it did not effect any thing. Any ideas??? Thanks in advance!!!

Well, if it's a sensor issue, you need to test them all, even the ones you replaced. Check out....

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

Also get a gauge and check your fuel pressure. Don't bother just pressing the valve to detect a squirt.

Also, disconnect every connector to the sensors. Check for corrosion and clean. Follow each wire bundle to make sure nothing got scraped, melted, twisted, or abducted by aliens.

The fuel pump ballast resistor is shown in the article that Saudade linked to. Its in the picture with the EGR solenoid.

If that resistor is acting up, your fuel pump will not be getting the proper voltage, which could lead to exactly the problems youre describing.

Word on the street is its cheap and easy to replace...in fact some people bypass them altogether as later models dont even have one.

Thank you all for your replies and thank you for the link. I had no idea what some of those sensors were. I will start testing them. Then I have one more question, does this 90 cherokee need all of these sensors to function or can they be bypassed. If so were can I find that info. out at. I live in a state the does not have emission inspections. I know alot of them are for emission, so are they necessary? I will keep everyone posted on my progress. Thanks again

UPDATE!! I bypassed the fuel pump ballast resistor that did not change anything. I also unplugged the EGR soleniod and plugged the vacuum line to it and EGR. The problem is still there. So that is my update for now, I will have to borrow a volt meter tomorrow so I can start on all the sensors.