2000 TJ 4.0, 5-Speed With P0300, P0302, & P0306 - Multiple Misfire

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2000Heep

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Location
Evergreen, CO
2000 TJ - I6 4L, 5 Speed Manual - 163K mi

P0300 P0302 P0306 - Multiple Misfire

This is our plow jeep and we occasionally use it to run around town.

I changed the head to a TUPY head in November 2022 due to loss of compression which was attributed to leaking valves.

New parts used: Remanufactured Head, Head Gasket, Head Bolts, Hydraulic lifters, pushrods, rockers, spark plugs (Champion 3412), coil pack, crank position sensor

The new, reman head, did the trick and instantly we got a major power boost from the engine that was never there before. In the process I discovered that the Crank Position Sensor wire was nearly severed so I replaced it with a MOPAR sensor. All was well with it and plowed our driveway etc no worries.

July 2023, all of the sudden it has developed a severe misfire in multiple cylinders with near complete loss of power.

I can smell gas when it is running, plugs have a new black soot on all 6 of them. It sounds to me like there is a timing issue... or maybe a short... or a sensor has failed

OBDII Codes - P0300 P0302 P0306 - Multiple Misfire

OBDII Powertrain Live Data at idle:

PCM PID
Fuel Sys 1- CL
Fuel Sys 2 - N/A
Calc Load - 9.8%
ECT - 142F
STFT B1 (-5.5%)
LTFT B1 (-33.6%)
MAP - 14 inHg
Engine RPM - 790
Vehicle Speed - 0 mph
Spark Advance - 9.5
IAT - 183F
TPS 18.4%
O2SLoc - O2S11/2S12
O2S B1 S1 - 0.840V
STFT B1 S1 - (-5.5%)
O2S B1 S2 - 1.100V
STFT B1 S2 - 99.2%

The Code Reader (Innova 3100RS) shows that it successfully monitored the following:
  • Misfire Monitor
  • Fuel System Monitor
  • Comprehensive Component Monitor
  • Oxygen Sensor Monitor
  • Oxygen sensor Heater Monitor

What I've physically checked thus far:
  1. Coil appears to make good spark on all 6 cyls by using a spark plug inserted in the coil boots and grounding it via jumper cable to the body ground.
  2. I tried a brand new coil to be certain and got the same results as with the existing (new in Nov 2022) coil.
  3. I don't see any issues with wiring
  4. Visual check of vacuum lines
What are my next steps to try to figure this out?

I can run a compression and leak down test if need be, I am good with a DMM and I have access to a power probe IV.

I'd like to diagnose the problem, not throw parts at it.

Appreciate everyone's help!!!!
 
2000Heep said:
2000 TJ - I6 4L, 5 Speed Manual - 163K mi

P0300 P0302 P0306 - Multiple Misfire

This is our plow jeep and we occasionally use it to run around town.

I changed the head to a TUPY head in November 2022 due to loss of compression which was attributed to leaking valves.

New parts used: Remanufactured Head, Head Gasket, Head Bolts, Hydraulic lifters, pushrods, rockers, spark plugs (Champion 3412), coil pack, crank position sensor

The new, reman head, did the trick and instantly we got a major power boost from the engine that was never there before. In the process I discovered that the Crank Position Sensor wire was nearly severed so I replaced it with a MOPAR sensor. All was well with it and plowed our driveway etc no worries.

July 2023, all of the sudden it has developed a severe misfire in multiple cylinders with near complete loss of power.

I can smell gas when it is running, plugs have a new black soot on all 6 of them. It sounds to me like there is a timing issue... or maybe a short... or a sensor has failed

OBDII Codes - P0300 P0302 P0306 - Multiple Misfire

OBDII Powertrain Live Data at idle:

PCM PID
Fuel Sys 1- CL
Fuel Sys 2 - N/A
Calc Load - 9.8%
ECT - 142F
STFT B1 (-5.5%)
LTFT B1 (-33.6%)
MAP - 14 inHg
Engine RPM - 790
Vehicle Speed - 0 mph
Spark Advance - 9.5
IAT - 183F
TPS 18.4%
O2SLoc - O2S11/2S12
O2S B1 S1 - 0.840V
STFT B1 S1 - (-5.5%)
O2S B1 S2 - 1.100V
STFT B1 S2 - 99.2%

The Code Reader (Innova 3100RS) shows that it successfully monitored the following:
  • Misfire Monitor
  • Fuel System Monitor
  • Comprehensive Component Monitor
  • Oxygen Sensor Monitor
  • Oxygen sensor Heater Monitor

What I've physically checked thus far:
  1. Coil appears to make good spark on all 6 cyls by using a spark plug inserted in the coil boots and grounding it via jumper cable to the body ground.
  2. I tried a brand new coil to be certain and got the same results as with the existing (new in Nov 2022) coil.
  3. I don't see any issues with wiring
  4. Visual check of vacuum lines
What are my next steps to try to figure this out?

I can run a compression and leak down test if need be, I am good with a DMM and I have access to a power probe IV.

I'd like to diagnose the problem, not throw parts at it.

Appreciate everyone's help!!!!
Click to expand...

I'd do a compression / leak down test next. I know you have a new head on there, but it's certainly possible that you could have gotten a bad head with a small crack in it.

I'd also thoroughly inspect the wiring. I've seen and heard of a lot of issues like this be the result of a fault in the wiring harness somewhere.
 
Chris said:
I'd do a compression / leak down test next. I know you have a new head on there, but it's certainly possible that you could have gotten a bad head with a small crack in it.

I'd also thoroughly inspect the wiring. I've seen and heard of a lot of issues like this be the result of a fault in the wiring harness somewhere.
Click to expand...

Chris, Thank you for your reply and I agree with you, I'll run the leakdown and compression test this weekend and post results.
 
I have performed a compression and leak-down test. I know that this test should be performed with the engine warm but this was not possible since the engine will will not run without the extreme missfire.

The test was performed at 40F ambient, after the jeep had been outside overnight at 20F.

Test
1​
2​
3​
4​
5​
6​
Cylinder #
Compression
135​
140​
135​
150​
140​
120​
PSIG
-10.0​
-6.7​
-10.0​
0.0​
-6.7​
-20.0​
% difference
1​
2​
3​
4​
5​
6​
Cylinder #
Leak
100​
100​
100​
100​
100​
100​
Reference Gauge
88​
93​
95​
96​
91​
95​
Leakage gauge
-12.0​
-7.0​
-5.0​
-4.0​
-9.0​
-5.0​
% difference

All testing was performed with the throttle open and all spark plugs removed.

Please let me know your thoughts on next-steps.
 
I chased multiple misfire codes and changed a lot of parts...coils, cap, rotors, plugs, plug wires. Finally replaced the crank position sensor with a Napa because there's no more Mopar for my 97.

Might want to check and see if you're getting 5v at the sensor using the FSM wiring diagrams.

-Mac
 
Mac,

Thank you for your reply. I have replaced the Crank Position Sensor (CPS) in November 2022, which I found had a severed wire. Soon as I did that the Jeep ran just fine. The symptoms of the broken wiring to the CPS was the fuel pump would not run. Changed the CPS and the issue was fixed (unfortunately the wire couldn't be repaired as the damage to it was right at the sensor body).

... the next thing that happened was July 2023 ...
  • All of the sudden it has developed a severe misfire in multiple cylinders with near complete loss of power.
  • I could smell gas when it was running (NOTE: running is a poor description as it would barely run due to the misfireing cylinders), plugs have a new black soot on all 6 of them. It sounds to me like there is a timing issue... or maybe a short... or a sensor has failed.
The fact that the Jeep went from running just fine and now has multiple misfire codes and near total loss of power along with the fact that the plugs were a nice tan color to now are covered in black soot makes me believe that the ECM has failed. The Jeep has 163K on it and is 23 years old. Also, when it developed the multiple misfire codes it was sudden, not a slow development which further makes me think that the ECM has died.

I'm inclined to purchase a new ECM based on having tested the sensors and all of them are within the FSM specs given.

I hate to just throw parts at something but from what I have inspected and have been able to rule out, the ECM seems to be the most logical point of failure.

Certainly would like to have your opinion as well as others if anyone has suggestions.

Thank you!

Sean
 
macleanflood said:
Timing chain?

-Mac
Click to expand...

Mac,

I had not thought of the timing chain... the loss of power and multiple misfire codes leads me to believe it's not the chain... My reasoning that I don't think it is the chain is it was running fine one minute and the next it was missing on 2 or 3 cylinders. Seems to me that if the chain was a problem all cylinders would be equally affected which I don't think is the case.

Am I thinking about timing chain as a possible culprit correctly or not?

Thanks,

Sean
 
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2000Heep said:
2000 TJ - I6 4L, 5 Speed Manual - 163K mi

P0300 P0302 P0306 - Multiple Misfire

This is our plow jeep and we occasionally use it to run around town.

I changed the head to a TUPY head in November 2022 due to loss of compression which was attributed to leaking valves.

New parts used: Remanufactured Head, Head Gasket, Head Bolts, Hydraulic lifters, pushrods, rockers, spark plugs (Champion 3412), coil pack, crank position sensor

The new, reman head, did the trick and instantly we got a major power boost from the engine that was never there before. In the process I discovered that the Crank Position Sensor wire was nearly severed so I replaced it with a MOPAR sensor. All was well with it and plowed our driveway etc no worries.

July 2023, all of the sudden it has developed a severe misfire in multiple cylinders with near complete loss of power.

I can smell gas when it is running, plugs have a new black soot on all 6 of them. It sounds to me like there is a timing issue... or maybe a short... or a sensor has failed

OBDII Codes - P0300 P0302 P0306 - Multiple Misfire

OBDII Powertrain Live Data at idle:

PCM PID
Fuel Sys 1- CL
Fuel Sys 2 - N/A
Calc Load - 9.8%
ECT - 142F
STFT B1 (-5.5%)
LTFT B1 (-33.6%)
MAP - 14 inHg
Engine RPM - 790
Vehicle Speed - 0 mph
Spark Advance - 9.5
IAT - 183F
TPS 18.4%
O2SLoc - O2S11/2S12
O2S B1 S1 - 0.840V
STFT B1 S1 - (-5.5%)
O2S B1 S2 - 1.100V
STFT B1 S2 - 99.2%

The Code Reader (Innova 3100RS) shows that it successfully monitored the following:
  • Misfire Monitor
  • Fuel System Monitor
  • Comprehensive Component Monitor
  • Oxygen Sensor Monitor
  • Oxygen sensor Heater Monitor

What I've physically checked thus far:
  1. Coil appears to make good spark on all 6 cyls by using a spark plug inserted in the coil boots and grounding it via jumper cable to the body ground.
  2. I tried a brand new coil to be certain and got the same results as with the existing (new in Nov 2022) coil.
  3. I don't see any issues with wiring
  4. Visual check of vacuum lines
What are my next steps to try to figure this out?

I can run a compression and leak down test if need be, I am good with a DMM and I have access to a power probe IV.

I'd like to diagnose the problem, not throw parts at it.

Appreciate everyone's help!!!!
Click to expand...

I had multiple misfires that were fixed by a @Wranglerfix pcm.

Might be worth talking to Mark about this.
 
So, I replaced the computer with a 'new' remanufactured computer that has a 30 day, no restocking fee, 100% money back, return policy on it.

No change ... it still sounds like it's coming apart... sound mechanical to me.

Anyone have suggestions what I should do next?

Appreciate your help and time.
 
OK - I found the root cause of the multiple misfires... Despite using break-in oil and assembly lube and following the break-in procedures the new lifters were found severely worn, all the way into the oil chambers and the cam was wiped out. That was after only a couple of hours in total of run time.

Now I have replaced:

Cam, Water Pump, timing chain and gears, lifters & pushrods & all soft goods. Also put in a magnetic drain plug.

I used Lucas straight 30 weight break-in oil & new filter... ran for 50 miles then I changed oil and filter again using Lucas straight 30 weight and will run it for a total of about 10 hours (using roughly 50 miles per hr x 10 hrs to approximate 500 miles to help ensure break-in). I will then change oil again back to 10W-30 and new filter.The purpose of this oil and filter change exercise is to try to ensure that I get any debris out of the engine and provide a good break-in before returning to standard multi weight oil.

Now it runs great and I was able to push the mega snow we recently received (40" of wet heavy spring snow at our house) and the neighbors etc. Our driveway is about a 1/4 mile long, plus all the neighbors and the jeep never missed a beat. I plowed for around 8 hours or so in total to deal with the snow.

In hindsight, I'd have swapped out the cam at the same time as the lifters on the first go-around but I'm not sure that I wouldn't have had the same failed lifter issue regardless. I guess all I can do is speculate at this point.

Let me know if you have any questions and I'll try to help.
 
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