I cant for the life of me figure out what is going on with my Cherokee. It is a 1996 xj with a 4.0 ho motor. It used to start, but would idle really crappy and RPMs would jump all over. After replacing the fuel pump yesterday it ran for the night but wouldnt start this morning. I have replaced a bunch of parts including: TPS, CPS, IAC, MAP sensor, Cam pos. sensor, Ign. coil, Temp sensor, Injectors, Plugs and wires, Fuel pump, Fuel filter, and have checked fuel pump relay and pressure at fuel rail is fine.

One thing i would like to know and may be the issue is I replaced the computer last week and was wondering if it needs to be flashed or anything.

Please help I have no idea what else to do

 

If you have the correct replacement computer (correct year), it should be plug and play.

Are you currently seeing the check engine light and if so, what are the exact code numbers? Even if you are not seeing a check engine light, you should check for codes. Below is how to do that on your 96.

When it doesn't start, you should do a bit of simple testing to see if you have a spark or a fuel problem or both. More on that below too. With yours being an intermittent start, this is not likely a fuse issue which I highlight in step #1.

Good luck and keep us updated!
----------------------------------------------------------
OBDII models (1996 and “SOME” 1997 models)

Put the key into the ignition, push down the odometer reset button, then turn the key to RUN with your finger on the button - and then release the button. The odometer will go through 1111111 through 999999, then display the car's serial number. It will then show the 2 digit error codes. A "5-5" will always occur to signal the end of the sequence. Some will flash the "1-2" code indicating a recent battery disconnect even if you haven't done it. Ignore these two codes, and mark down all others.

The 2 digit code that you will get using this technique is helpful, but it is not as specific as the full PXXXX code, which is only available using a code reader or scan tool, so generally I recommend using the code reader or scan tool. But if you have a CEL and don’t have access to a code reader or a scan tool, try the odometer technique to point you in the right direction until you can gain access to a code reader or scan tool

Note: The above OBDII odometer technique works only for 1996 and early 1997 model XJs, so while it might work on one 1997 XJ, it might NOT work on another! Once Chrysler made the change during the 1997 build year, for anything built after that date through 2001 you will need either a code reader or a scan tool to retrieve the codes.
--------------------------------------------------------------------
1. Check all fuses. Don't forget about the critical fuses in the power distribution center (the black box) under the hood!

2. Listen for the fuel pump. Turn the key to the ON position (not start). The fuel pump should energize and run for approximately 2 seconds by design. If you don't hear that, you need to address the fuel pump circuitry.

3. Check for spark. Remove a spark plug. Keep it attached to the plug wire. Place the plug electrode near a good engine ground. Have a buddy crank the engine while you watch. You are looking for a strong, BLUE, snapping spark. Yellow/orange/white indicates a weak spark which may not be strong enough to start the engine (weak spark is usually related to the ignition coil).

4. IF spark is good (and ONLY if), then introduce a small amount of gas or starting fluid into the intake. If the engine starts and runs with this technique, you have identified a "fuel delivery" problem.

 

I have checked the codes using the key on/off/on/off/on method and the only ones it is spitting out are codes: 11 and 22

When i replaced the fuel pump yesterday, my jeep ran fine and i even drove it a couple miles to test it out. At that time the only code showing was 22.

I believe 22 is the coolant temp. sensor which I replaced a couple days ago.

 

tjwalker has the right idea in the bottom of his post. Do the rest of that and then maybe we can come up with something.

 

I have checked all the things he had suggested and all of them checked out fine.

I think it may be a fuel air mixture problem and i think i found an intake manifold leak out of the gasket so this may be the problem.

The only thing i can think of after replacing all these parts

 

Checked the o2 yet?

 

yeah replaced upstream and downstream o2 sensors.. dont think there is much i havent done

 

Do you have spark, and if so, is it weak (yellow) or strong (blue)?

 

I have strong spark and am currently replacing the intake/exhaust manifold gasket.

 

replaced the gasket and that didnt do anything. I wonder if it is the fuel pressure regulator.

 

Alright this is pissing me off.

I just replaced the whole fuel sending unit in the gas tank and nothing happened. i have strong spark and it gets plenty of fuel to the rail.

It has to be a fuel/air problem or something.

Does anyone know if the charcoal canister screws with anything like this?

 

Ever figure this out?

 

Ended up being the ignition.