Misfire on cylinder 4 on my 2004 PT Cruiser

AIR & FUEL FILTERS NEED CHANGED, MAP SENSOR CAN BE FAULTY ! PUT SOME FUEL INJECTOR CLEANER IN TANK, THE GOOD STUFF ! DO ALL THIS, SEE HOW IT DOES .

Trouble Code: P0301

Cylinder No. 1, 2, 3 or 4 Misfire Detected

Trouble Code Conditions: Engine is running; atmospheric pressure, fuel level, battery voltage, engine speed, engine load are above minimal predetermined specifications; the engine is not in fuel cutoff and intake air temperature and coolant temperature are within normal operating ranges; there are no DTCs relating to ECT, CMP, CKP, MAP or IAT Sensor, to Crank rationality, to Crank Sensor Learn invalid, or to System Voltage. If total misfires detected are greater than 7% during the first 1000 rpm, or are over 3% after the first 1000 rpm, or are 25% during any 200 rpm with suspect cylinder misfire counter more than 80% and no other cylinder misfire counters above 80%, this DTC will set. The MIL will flash after first trip occurrence and will be steady after second trip.

Possible Causes:


Fuel system problems existErratic CMP or CKP Sensor signalsIgnition system problems existEngine mechanical problems existPCM has failed

CLEAN FUEL INJECTORS SEE IF THAT HELPS.IF NOT COULD HAVE BAD FUEL INJECTOR OR FUEL INJECTOR ELECTRICAL CONNECTOR COULD HAVE A SHORT.DO A COMPRESSION CHECK ON THAT CYLINER COULD ALSO HAVE LOW COMPRESSION DUE TO BAD VALVES OR INTAKE MANIFOLD LEAK AT CYLINDER NUMBER 4.

The blinking light means that the cylinder or cylinders are misfiring, the first step is to see if it needs a tune up, bad plugs or wire will cause this. if you go to an autoparts store and have them scan the computer , they will give you a print out of the codes, i will bet theres a few misfire codes. the codes will tell you exactly what cylinder is actting up and from there you can check the wire and plug.

Misfire could be a number of things:
a) spark plugs - change them if used over 15K miles - inspect/regap.
b) spark plug wires - change them if over 15K miles - inspect
c) ECM (electronic control module) - test with HEI (high energy ignition) tester.

The shaking tells me that the engine is running on less than its normal compliment of cylinders - the shaking is produced by the imbalance caused in the engine by one (or more) cylinder(s)
not firing at all.

The "Check Engine" light probably is coming on due the the misfire condition. Go to Pep Boys or
Advance Auto Pats, where they'll tell you (free) your codes causing the "Check Engine' light to be
lit - the code coming from your truck's computer will probably be one or more of:
P0300 - Random/Multiple Cylinder misfire detected
P0301 - Cylinder 1 misfire detected
P0302 - Cylinder 2 misfire detected
P0303 - Cylinder 3 misfire detected
P0304 - Cylinder 4 misfire detected
P0305 - Cylinder 5 misfire detected
P0306 - Cylinder 6 misfire detected
P0307 - Cylinder 7 misfire detected
P0308 - Cylinder 8 misfire detected
P0313 - Misfire detected with low fuel

CODE PO304 - CYLINDER 4 MISFIRE DETECTED. POSSIBLE CAUSE BAD SPARK PLUG .FAULTY OR STOPPED UP FUEL INJECTOR.BAD IGNITION COIL.

I would start by having your codes cleared. If a fouled plug was the culprit, the pcm may not have reconized that it was fixed.

Try running a bottle of sea foam through it. You could have a sticking fuel injector.

As a last resort , have a compression test done. A crack in the clyinder head could also cause this issue.

I hope this gets you started :)

Do you know how check the engine codes? Turn the key 3 times and the codes will be displayed where the odometer number is displayed.
If the code is 302 it is spark plug mis fire.
It could be a bad fuel injector.

anything from bad wire .plug or fuel delivery problem to cylinder 1pull plug and c if fouled -also test wire for break

440 and 441 relate to the evaporative prurge flow system and 303 is a misfire detectec in cylinder 3.