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Old November 24th, 2017, 15:14
deproson deproson is offline
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2000 XJ wont fire

So a little back history to what got me to this point.

I have a high mileage 4.0 with 260,000 miles. The other day I was driving to work and it started to have a slight miss. I continued to drive and then it develop a severe miss and had almost no power and felt as if the throttle would cut in and out. So I pulled over hooked up my OBDII scanned and pulled four codes.

1. P0300 Multiple cylinder misfire
2. P0301 #1 misfire
3. P0306 #6 misfire
4. P0122 Throttle/Pedal position sensor A circuit low input

So I took note of these and erased them and continued to drive to work. As I pulled back onto the highway and as the motor went above 2000 RPM the CEL illuminated so I pulled back over checked what it was again and it was the same as above. At this point I was close enough to work so I limped it along until I made it to work.

Got to where I work hooked up my fuel pressure gauge and have about 48 PSI. Pulled my fuel rail out and pressurized the fuel rail and three injectors were seeping. So I ordered new ones and replaced all six.

I also replaced my spark plugs with OEM spark plugs at that time.

Reset the PCM and drove it home with no issue. The problem seemed to have gone away. Until the next morning I take it to work and not three miles down the road I get the same symptoms as before. I continue to drive to work and do some further troubleshooting.

At this time I start to troubleshoot the coil. I pulled the coil and spark plugs and turned the motor over. All plugs had a nice blue arc and I also checked the spark plug gap. All were in spec.

So the next thing I did was check the harness from the PCM to all sensors that are in the engine bay. The engine harness is pretty crispy but checks out with no problems. PCM voltage to sensors is right where it should be the injectors are pulsing and have the correct voltage. I have a buddy with the same year XJ as mine and borrowed his PCM to see if would go away. I put his PCM in and have the same issue.

Now this is where things get weird. I put everything back together and have a code for the CPS along with all the other DTCs listed above. I DID NOT BUY AN OEM CPS SENSOR, I know this is most likely the culprit. The thing that is weird is that now when you crank it over it seems as if the motor is trying to fire at the wrong time and sounds like it is backfiring in the intake and is fighting itself while trying to start. If you unplug the CPS and or the Cam position sensor it turns over like normal. I replaced the NON OEM CPS with a replacement from the company I bought the last one from with the same symptoms. To me I find it hard to believe that I got to bad sensors. Anything is possible though.

Now I'm waiting on my OEM Crank sensor, Cam position sensor and a TPS sensor to hopefully fix this issue. The only reason I bought a part store crank sensor was to try and get it home. If this OEM one fixes my issues then lesson learned.

If it doesn't fix it my next step is going to be to check the timing chain, I dought this is the issue but if the replacement of the sensors doesn't fix it I'm at a loss as to what the issue is.

Since it has been down while waiting for the parts to come in I have since pulled the engine harness and cleaned it up fixed a few broken connectors and re loomed and pulled apart all the crispy wires. Put it back in the jeep problem is still there.


Has anyone else had these same issues?
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Old November 25th, 2017, 19:25
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Tim_MN Tim_MN is offline
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Re: 2000 XJ wont fire

Cheap crappy Chinese clone CPS that don't work right ? Yes, that is a very common problem.

Install a genuine Jeep CPS, and solve the TPS trouble code, and it should be fine.
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Old November 25th, 2017, 19:26
deproson deproson is offline
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2000 XJ wont fire

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Originally Posted by Tim_MN View Post
Cheap crappy Chinese clone CPS that don't work right ? Yes, that is a very common problem. Install a genuine Jeep CPS, and solve the TPS trouble code and it should be fine.


I hope so. Iíll have all the parts Monday. Iíll post an update.


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