First off i have a 1996 cherokee and i cannot figure out what is wrong with it. When you first start it it runs completely fine for about 3-4 minutes then it starts acting like it’s loading up/misfiring. When trying to drive it it almost sounds like it’s back firing out of the air box and has no power what so ever sometimes i can barley drive it. The strange thing is if i start it it will run fine for 3-4 minutes then it will start to run really bad then if i shut it off and turn it immediately back on it will run fine for 3-4 minutes. cannot figure out what’s wrong with it. Here is a list of parts i have changed. Throttle positioning sensor, Intake air control valve, distributor and plugs, and ignition coil. anyone have any ideas? not throwing a check enlightens either.

 

When did you replace the crank sensor?

 

haven’t replaced crank sensor only read being everything i’ve read said it wouldn’t run at all if it was a bad crank sensor

 

Bad o2 sensor or blown fuse for the O2 heater circuit?

 

I like O2 sensor problem for this. But more than that I like actually testing to verify before buying one and swapping it in.

 

Could try unplugging the coolant temp sensor which would cause it to stay open loop, to see if it stops choking.

 

use an OBD2 code reader to check for any codes, sometimes O2 sensors dont trigger a check light

the BAFX reader works on a '96, cost me about $30

 

This can be caused by two things. A worn out O2 sensor, which should be replaced at least every 100K and preferably every 50K. Also a crack in the exhaust manifold causing air to get sucked into the exhaust which would then give a false O2 sensor reading

 

Do you have a scanner you can read real-time sensor values?

Check the coolant temp sensor when the engine is cold. Compare to ambient temperature. They should be the same. If no scanner, you can ohm out the sensor with a multi-meter, and find the temperature on a sensor/ohm chart (for a Cherokee), and know if it's out of spec. And do the same when the engine is warm. You can shoot the metal part where the upper radiator hose connects, using an infra-red thermometer and get an approximately close engine temp (e.g. 195*).

I didn't hear anyone suggest checking/cleaning the hole area beneath the EGR valve. It's probably all carbon'd up. IDK if that would cause the specific problem you're having, but it could affect operation if it is plugged up under there like they often become. Remove it and clean out with screwdriver or other instrument. Check EGR while at it too. And check the vacuum diaphragm

All the other things that came to mind have already been mentioned above. Lot of good suggestions. You've done what I would have started with.

 

As temp rises the cps skip crank angle but usually not in 3 or 4 min. There is no EGR on the 96. The best bet is a scanner with live data to see all the sensor data.

Unplug the front o2 sensor and see how it runs.