Another 03 Liberty with P0300

[Pell]

I have a 2003 Jeep Liberty Sport 3.7
For the past 4 months I have been dealing with totally random multiple misfires (P0300). Here is what I have observed and have done so far.
The misfires seem to be totally random and I have not been able to find anything that really points to the trouble, but one thing I noticed was that it seems to happen more often when I am coasting down a hill above 50 mph. This is not always the case but I have observed this P0300 code during this condition several times.
I have replaced the spark plugs, coil packs, oxygen sensors, camshaft sensor and crankshaft sensor.
It seems so random. I was thinking maybe the PCM but after speaking with a shop that remanufactures Powertrain control modules, one guy said that he has not seen a PCM cause that condition before.

 

[J-Thompson]

May be a bad cat. converter
There is an issue with some of the late
model Ford's with the 5.4l gas engine
getting plugged up cats and doing all kinds
of strange things

 

[Pell]

I guess it could be a cat but I'm thinking it's not in this case because if it was a cat then the problem should be a little more consistant. Such as maybe the problem would arrise when the cats got hot or maybe always prior to them getting hot. The missfires I am experiencing seem to be happening so randomly. Sometimes within the first couple miles of driving the Jeep and sometimes hundreds of miles in between misfires. Very random.

 

[BigRich201]

does it just throw the po300 or does it throw the other codes which tell you what cylinders are misfiring. i had this issue a while ago. i had the po300 followed by po301 and po305 showing its the 1st and 5th cylinders misfiring. all the plugs and coils were fine. it was just a little hiccup. i cleared the code and never saw that code again.

 

[Pell]

It varies. Most of the times its just p0300 but other times it shows a variety of po301 through p0306. Never the same thing twice. It's been doing this now for 4 months.

 

[randrson]

Just throwing out another possibility. In my intrepid I had the p300 errors, and p30X error, and it was the result of a leaking injector. it would sometimes throw it during driving, starting, hot /cold you name it. did you look at your plugs when you pulled them to see if any were fouled. you would know it more so if engine was hot and a bit harder starting after it sits.

 

[mirwest]

Do you get this fixed? I have been working on the same thing for a year

Thanks Frank