1999 xj 4.0 2wd limited aw4 220,000 miles
I have a misfire on cylinder 3 code p0203. It is a misfire all the time, cold and hot, once i start the jeep it misfires. It drove fine for the first 2 years of having this jeep and just started misfiring about 3 weeks ago. I have ran into this problem before on my 2001 xj and that one ended up being a bad driver in the PCM. I am going through this 99 and am trying to figure it out if i need another PCM for this one or not. So far these are all of the checks i have done to narrow down the problem.
1. Cleaned 3 big connectors for PCM and cleaned the grounds right next to where pcm is mounted. Battery is new, All Cables underhood are new, (Jeep Cables Upgrade).
2. Checked for spark on #3. Have spark and cleaned cap, rotor and checked wires for break. All spark plugs, cap, rotor and wires are new and have about 15,000 miles on them. Pulled Plugs and they look good, Will attach a picture to show how they look.
3. Original fuel injectors had cracks in them so i thought at first it would be the injector so i replaced them with upgraded Bosch 4 hole injectors no difference. Swapped injector #3 with #2 no difference still a misfire on cylinder #3.
4. Checked injector connecter with voltmeter, I am getting 13 volts to #3 injector wire while motor is running.

Checked ignition coil and it has some cracking in it. It looks to be the Original coil. I don't know if that would cause just one misfire or a misfire on every cylinder. Or no spark at all.

Cps is new Napa unit with 15,000 miles on it

What does this narrow it down to? PCM has a driver shot in it. Or i have a break in the ground wire from injector connector to PCM. Any other ideas? Thanks for the help.

 

Read your post a couple times in case I missed it but didn't see that you had checked the compression.

 

Have not checked compression, i assumed with the engine running fine for 2 years that something that catastrophic would not happen, but i could be wrong. Engine is not making any noise it is a very quiet motor and always has been well maintained even before me. I should get a compression gauge just in case.

 

Wouldn't have to be catastrophic. The thing does have a quarter million miles on it. Could be a burned valve, leaking head gasket.
you've checked a lot of the possibilities with no results, time to move on to other stuff and eliminate them.

 

Well, the P203 is an injector circuit code not an ignition code. Still it's good to check everything.

https://www.700r4transmissionhq.com/...jeep-cherokee/

Since you replaced and swapped injectors with no change, I think we can rule out the injectors.

Did you back probe the injector connector with a volt meter? Having battery voltage suggests the B+ is good.

The injector then grounds through the PCM. You can trace the ground (continuity) from the injector connector to the PCM. #2 FI ground is TAN, and connects to PCM connector C2 Pin B15. Carefully check the pins on the connectors, Make sure they're not bent, pushed in, corroded, etc. While the PCM connector is off, check the ground circuit to the other injectors.

 

I did take the pcm out and clean both the pcm and big 3 connectors with contact cleaner and the pins seemed to be fine. Not broken and no corrosion. I put Dielectric grease in also just to be sure. I checked the fuel injector connector with a volt meter while the motor is running and got 13 volts from the positive side. How would i back probe for the ground side? How do i do that with a volt meter? Thanks.

 

The ground would be a continuity check using OHMS on your multimeter using the lowest scale. I'd pull the connectors off, then probe the 2 corresponding pins. You should see very few ohms (zero is ideal).

Test the meter first by touching the 2 probes directly together and note the reading. It should be zero or very close to it. Then stick one probe into the FI connector on the TAN wire side (not the orange) and the other probe into the PCM connector Pin B15. Polarity won't matter for this.

If you get a very high resistance reading, or doesn't read anything, you likely have a break somewhere in the tan wire.

 

I have not gotten around to more diag on this yet but i have been driving the Jeep recently and i am now getting a flashing check engine light when driving and i have 3 codes now. Code P0300, P0303, and P0305. Would this still reframe to possibly the broken wire or bad pcm driver on cylinder 3. Or does this show a problem in another area? Thank you

 

I am also not getting the original code i had before P0203.

 

Aftermarket CPS. Went through 4 already. Can't buy Mopar CPS, they're no longer available. Got lucky with the last one installed by a Napa service center in New Mexico. Do a FULL reset when you put the new one in. That means disconnecting the battery and leaving the headlights on for 20 minutes. Hope for the best in the CPS lottery.

 

The CPS is a Napa one that is going on 2 years. I have the original mopar one that is 24 years old i don’t think it is bad. I will try to swap them to see if it changes anything. Thank you for the input

 

Finally got around to working on the jeep again, it has been cold here in Nashville.

1. First off i had a new Mopar cps in my parts stash so i replaced the napa cps with this new Mopar one with no luck of change.
2. Second i took apart the fuel injector wiring harness running from the ECM to the fuel injectors to look for a broken wire for injector #3. No exposed or broken wiring.
3. I checked the continuity OHMS with my multi-meter using pin 5 at the ECM and the ground pin at the fuel injector pigtail for injector #3 and got a resistance of 0.0.

So at this point i will go to the parts store and rent a noid light kit and see what my next step is to see if i need a PCM or not.

 

You could do that. Or you can move the injector to see if the dead hole follows the injector. If it does, bad injector. If not, you've already verified continuity in the wiring, so likely the ECU.
Edit: did you verify 12v key on at the injector connector on the other wire?

 

Yup already swapped injectors #2 and #3 with no change. So ecu it must be then.

 

I didn't see if you mentioned it already, but one wire on the injector connector is +12v key on and the other is pulsed ground from the ecu. Verify +12v before condemning the ecu.