Allpar Forums banner

1 - 9 of 9 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter #1
I'm at a loss here guys. My son bought his first car a 03 pt Cruiser Gt 4 cylinder with about 80,000. We knew it need a little work but nothing major and there were no check engine codes. Well a misfire on cylinder 4 code came up months later so I figured I'd take care of it for him. I've had the coil pack, plugs and wires, injectors and cam sensor all replaced on at a time and that code is still there. Unfortunately I live in an area with emissions so this has to be taken care of but neither I nor my mechanic can figure out what do do next. Please any suggestions will help. Thanks in advance.
 

·
Registered
Joined
·
4,787 Posts
. . . . We knew it need a little work but nothing major and there were no check engine codes. Well a misfire on cylinder 4 code came up months later so I figured I'd take care of it for him. I've had the coil pack, plugs and wires, injectors and cam sensor all replaced on at a time and that code is still there. Unfortunately I live in an area with emissions so this has to be taken care of but neither I nor my mechanic can figure out what do do next. . . . .
So is the misfire setting code P0304? Is the engine normally aspirated or turbocharged?

I would suggest finding a mechanic / technician that knows how to use a scan tool and interpret short term and long term fuel trim values. Also the upstream oxygen sensor signal needs to be evaluated as it should be oscillating from a lean to rich to lean air - fuel mixture value. Something could be skewing a sensor value and cause the air - fuel mixture to go outside a normal range and create a misfire condition.

It is also possible that there is a mechanical problem with cylinder #4. You could have a broken ring which is causing low compression. You could have a valve that is sticking and not closing properly or a burned valve. This would affect compression.

Lots of possibilities which require pinpoint diagnosis. Don't fire the parts cannon any more until the issue is identified.
 

·
Registered
Joined
·
1,243 Posts
Did you use an oem cam position sensor and did you use copper champion spark plugs? Mopars like oem sensors and no spark plugs have been found to be as reliable as the copper champions.

A bottle pf techron in the fuel tank would not be out of place in my opinion.
 

·
Registered
Joined
·
3 Posts
Discussion Starter #5
To be honest I'm not sure what brand parts were bought other then they were all purchased Orieleys. I did however put a bottle of techron in the tank when I fueld up on the way to the mechanic as per his suggestion.
 

·
Registered
Joined
·
8,268 Posts
What gap did you set the spark plugs on? I found out via a buddy that my 03 GT ran best on a .040 gap.
 

·
Super Moderator
Joined
·
21,620 Posts
OEM parts are an important consideration. A premium set of store-brand plug wires should be OK, but you want the specified spark plug type (Champion Copper+ RE14MCC5).
A set of plugs may not pick on one cylinder to misfire, which is why you want to diagnose this. Misfire is either because of spark, fuel or mechanical issues.
A cylinder leakdown test will be more accurate than a cranking compression test.
Hearing a hiss of air at the tailpipe would indicate a leaking exhaust valve. A hiss of air at the throttle body would indicate a leaking intake valve and a hiss of air at the oil filler cap hole would indicate leaky rings (perform a wet test if this is the case).
If it does turn out to be a leaky valve/seat, installing a reman head at this mileage might be the best option.
 

·
Registered
Joined
·
160 Posts
Its VERY easy to diagnose a misfire, so my first suggestion is find another mechanic.

You have basically eliminated the ignition and injectors as a source by replacing all the pieces, but that doesn't actually mean its still not a problem.
You need to check compression. A leak-down check is better. You need to verify spark is present.
And then you would need to check fuel pressure and fuel pressure loss when the injector is activated to see if its actually flowing as it should. Its possible a wire or driver in the PCM has failed for the injector so its not firing.
 
1 - 9 of 9 Posts
Top