Cylinder Misfire P0303

johnboy89 · **Posted:** Wed Sep 10, 2008 8:19 pm

I recently purchased an 05 liberty with 35,000mi. I keep getting a cylinder misfire code on cylinder 3. I have replaced the coil and plugs, but the code will come back eventually after being reset. Sometimes it will run rough(idle) and then after that it will set the code. I did a compression check and cylinder 3(140PSI) was about 50 PSI lower that cylinder 1(190PSI). With this being said and after doing some research it appears that the intake valves are problems on this year vehicle. Before I dump it off at the dealer I wanted to get some thoughts on it.

Thanx

myjeepwalks · **Posted:** Wed Sep 10, 2008 10:12 pm

What about the rest of the cylinders, what's the psi on those? Does it have a dead miss or just run a little rough?

johnboy89 · **Posted:** Thu Sep 11, 2008 6:12 pm

Well I checked the three cylinders on the drivers side again tonite. What's interesting is when I first checked cylinder 3 it was 140PSI as stated above, but when I checked it again it was up to 190 PSI. The other two cylinders (1 & 5) were both 190 PSI consistently. Could the fluctuations be the result of a sticking valve/spring? I'm not sure if it's a miss or more of a rough idle, but the vehicle almost always seems to idle rough, but once you give it gas seems to be ok. The other day it was pretty bad(light came on) and I would say that was a miss, but it's definetly not there all the time.

Thanx

myjeepwalks · **Posted:** Thu Sep 11, 2008 7:45 pm

I think the valve springs actually break not just stick. You sure it's not a clogged injector? With it running put a pry bar against the injector and put the other end up to you ear. You should hear it ticking, compare it with the other 5.

jelohead · **Posted:** Thu Sep 11, 2008 7:56 pm

i got cylinder misfire codes also.....wound up having BOTH heads replaced under warranty!

johnboy89 · **Posted:** Thu Nov 20, 2008 5:38 pm

UPDATE

Well since my last post I swapped injectors with cyliner 1 and the code still stayed with cylinder 3.

So off to the dealer it went yesterday. They could not find a problem with cylinder three compression nor get it to duplicate. He noticed that I had autolite plugs installed and stated that they have had numerous problems with them. The only issue with that is I pulled the original plugs because of the misfire and they were original NGK's. Calls me back in the afternoon and states that he let it idle for a long time and he was getting multiple cylinder misfires, not enough in a row to set a code though.

They are recommending to do the fuel system flush and plug chage for the tune of $250.

In my mind I know this code is going to come back, but feel that I have to take this first step and when it re-occurs it doesn't come back until it's fixed.

Thoughts?????

jelohead · **Posted:** Thu Nov 20, 2008 5:43 pm

before you agree to any service/work, ask them their policy if the repairs they perform dont correct the problem. will the work be free if the problem continues? also, tell you "know" someone that had the same codes and wound up with 2 new cylinder heads, maybe they can look further into possible head cracks or defective seals, etc

tjkj2002 · **Posted:** Thu Nov 20, 2008 5:49 pm

johnboy89 wrote:

UPDATE

Well since my last post I swapped injectors with cyliner 1 and the code still stayed with cylinder 3.

So off to the dealer it went yesterday. They could not find a problem with cylinder three compression nor get it to duplicate. He noticed that I had autolite plugs installed and stated that they have had numerous problems with them. The only issue with that is I pulled the original plugs because of the misfire and they were Champions. Calls me back in the afternoon and states that he let it idle for a long time and he was getting multiple cylinder misfires, not enough in a row to set a code though.

They are recommending to do the fuel system flush and plug chage for the tune of $250.

In my mind I know this code is going to come back, but feel that I have to take this first step and when it re-occurs it doesn't come back until it's fixed.

Thoughts?????

They need to be testing the driver that controls the cylinder #3 coil in the PCM,may take awhile but that seams to be your problem.Had a chevy 5.3 with the same problems you are having last week and it took about 5 hours of running it to get the driver to hickup enough to set a misfire code,then charged them the diagnostic time and sent them to the dealership since we can not program PCM's.

johnboy89 · **Posted:** Thu Nov 20, 2008 7:17 pm

tjkj2002 wrote:

johnboy89 wrote:

UPDATE

Well since my last post I swapped injectors with cyliner 1 and the code still stayed with cylinder 3.

So off to the dealer it went yesterday. They could not find a problem with cylinder three compression nor get it to duplicate. He noticed that I had autolite plugs installed and stated that they have had numerous problems with them. The only issue with that is I pulled the original plugs because of the misfire and they were Champions. Calls me back in the afternoon and states that he let it idle for a long time and he was getting multiple cylinder misfires, not enough in a row to set a code though.

They are recommending to do the fuel system flush and plug chage for the tune of $250.

In my mind I know this code is going to come back, but feel that I have to take this first step and when it re-occurs it doesn't come back until it's fixed.

Thoughts?????

They need to be testing the driver that controls the cylinder #3 coil in the PCM,may take awhile but that seams to be your problem.Had a chevy 5.3 with the same problems you are having last week and it took about 5 hours of running it to get the driver to hickup enough to set a misfire code,then charged them the diagnostic time and sent them to the dealership since we can not program PCM's.

I would agree, but the intermittent lower compression reading makes me think otherwise. They did say they are going to update the PCM with the latest software for free though.

k99jk99j · **Posted:** Thu Nov 20, 2008 10:35 pm

ask them what the misfire count per minute is at idle. if it is anywhere near 10 you qualify for TSB 09-007-06. which involves replacing the cylinder head valves and locks. mike

johnboy89 · **Posted:** Thu Jan 08, 2009 5:13 pm

Just to update the post I had the TSB performed at the dealer about a month ago and the code has not come back since. They replaced all of the intakes valves and locks on both cylinder heads.

Thanx for the help

adamkrz · **Posted:** Thu Jan 08, 2009 9:40 pm

johnboy89 wrote:

Just to update the post I had the TSB performed at the dealer about a month ago and the code has not come back since. They replaced all of the intakes valves and locks on both cylinder heads.

Thanx for the help

Had new intake valves put in last month, So far no engine light, Very pleased with the dealer for the work only costing me the 100 dollar deductable for a vehicle that's over 5 years old..

C co Crusader 2/127 · **Posted:** Fri Jan 09, 2009 10:30 pm

try checking the gap on the spark plug if all else fails

Cylinder Misfire P0303

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