WJ 4.0 running rough intermittently - JeepForum.com
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post #1 of 3 Old 06-18-2018, 06:27 PM Thread Starter
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Wj WJ 4.0 running rough intermittently

I have a 02' 4.0 that intermittently runs very rough. It feels like a 2 or 3 cylinder misfire but the only misfire code i get is for cylinder 4. It never runs rough when the engine is cold, only when its warmed up. I also have an o2 sensor code for B1S1 but when I looked at the ecu live data while the engine is running rough, it is still on open loop so the o2 sensor should not have any effect. I recently rebuilt this engine about 4 months ago and this problem has kept getting worse. Here is what I have tried so far.

New copper plugs
New BWD coil pack
New BWD cam sensor
New BWD crank sensor
swapping injectors to see if the misfire moves to a different cylinder
I have checked the injector pulse when its running rough and it checks out okay.
Compression test on cylinder 4 - 130psi
Pressure tested the cooling system and looked in number 4 with a scope, pressure held and no coolant leaks were seen.
I looked over the wiring and did not see anything melted or cut.

The only thing I can think of next is possibly the ECU. Any thoughts would be much appreciated.

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post #2 of 3 Old 06-18-2018, 07:23 PM
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Post all codes use a scanner!!!! .
We can utilize the o2 info even if PCM is not using it. So post B1S1 voltages.

Is the engine reaching temp? NO LOWER THERMOSTAT...!!!!
What brand plugs?

live data - ECT, Fuel Trims- long and short, MAP, and o2 sensor voltages.

FYI sensors come from jeep esp CPS and CMP

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 3 Old 06-18-2018, 08:35 PM Thread Starter
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Codes are P0031,0132,0304

B1S1 is reading 1 volt. The engine is reaching about 205 degrees. The MAP is reading 7 psi. There is a schraider valve on the fuel rail. The plugs are NGK's. The fuel trims are reading 0 percent all around.
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