Intermittent misfire cylinders 2 & 3

[Spud]

Hello all,

I haven't been on the forum for quite some time but I recently started having trouble with my entirely stock (I know it is sad) 2004 Rubicon (4.0L TJ). I have approximately 76,000 miles and do routine oil changes and maintenance. The problem started when, at normal idle, I was hearing a metallic knocking sound. Using an automotive stethoscope I narrowed the sound to coming from the exhaust system, specifically near the front (engine side).

Shortly after this it started throwing codes and the check engine light came on. Using a code reader I found that it was showing P0302-CYLINDER #2 MISFIRE and P0303-CYLINDER #3 MISFIRE. I replaced all the spark plugs and inspected the old ones and saw nothing unusual (clearly not an expert though) and still have the problem. I also inspected the coil rail and it appeared to be fine.

The Jeep runs okay as long as I do not accelerate hard or put a load on it. As soon as a load is put on it, it loses power, starts bucking and the check engine light begins to flash.

I am thinking that my mini-catalytic converters are plugged. Does anyone have thoughts on this? Also, if it is the mini-catalytic converter, instead of replacing them (approximately $400) what about clearing out the obstruction and re-installing them? Will this cause problems for my engine computer or for emissions testing?

Thank you in advance for any advice.

 

[kingmega]

U can hollow out ur converters With no problems assuming u don't live in a place that requires emissions tests but i seriously doubt ur trouble is from ur coverter just because ur coils looked fine does not mine they r its just me but i would start at coils they r most likely where ur problem is start there

 

[JPNinPA]

You need the cats to run properly. Hallow them out and you will have issues with warmup and mpg, throw more codes and be breaking federal law. They are more likely to fall apart themselves before they clog. I doubt they are clogged unless you were burning oil or gas with lots of additives.

What brand and part number of spark plugs? It makes a big difference.

Were the plugs seated and torqued properly?

Are the boots over the plugs and in good condition?

Besides plugs you could have dirty leaky injectors or an intake/ exhaust leak.

The ticking prior could be a leak. When at idle what RPM does it stay at?

 

[69jeepcj]

I have had miss fire codes for a bad o2 sensor on a ford ranger.

 

[Spud]

So I finally had enough time off to work on the Jeep. I got the mini-catalytic converters off and they had in fact melted and plugged up the exhaust. I ordered a new set up which should get here Friday. For now I chipped out the honeycomb section and the Jeep runs perfectly. It does not throw any codes and no misfires! It does show an "error" on the catalytic converter which should be fixed as soon as the replacement is installed. Thank you all for the assistance.

 

[Rachel Kent]

Hey all I have a 2000 Jeep grandcherokee Laredo 4.0 shut it off on Thursday had no problem with it then. Went to start it friday it cranks an cranks no spark so I started with a non name brand crankshaft sensor still nothing replaced the cam sensor still nothing replaced the coil pack reset computer runs like crap but got it to throw 4 codes P1391 P0301 P0302 P0303 can anyone help me please.

 

[JPNinPA]

Hey all I have a 2000 Jeep grandcherokee Laredo 4.0 shut it off on Thursday had no problem with it then. Went to start it friday it cranks an cranks no spark so I started with a non name brand crankshaft sensor still nothing replaced the cam sensor still nothing replaced the coil pack reset computer runs like crap but got it to throw 4 codes P1391 P0301 P0302 P0303 can anyone help me please.

Use OEM crank sensor and make sure it has a paper gasket/disk

 

[JPNinPA]

Use OEM crank sensor and make sure it has a paper gasket.



Disconnect the POSITIVE battery Terminal and touch it to ground ( not the battery negative terminal ) for 30 seconds. The engine block or the A/C compressor pump will work as a ground. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory.

Reconnect the Battery Cable
Turn Ignition Switch to the “On” position but DO NOT start the engine
Turn Headlight “On”
Turn Headlights “Off”
Turn Ignition Key “Off”


The PCM Adaptive memory has now been flashed, or erased from the PCM.

When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory.

When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”.

The PCM will collect data for Adaptive Memory for the first 50 Wa