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P0303 Misfire Diagnosis on 2002 PT Cruiser with Low Cylinder 3 Compression

Model: 2002 PT Cruiser Fault Code: P0303 Posted: 2011-07-06 11:39

My 2002 PT Cruiser, with 148,000 miles, suddenly started running rough at idle. The next day, the engine lost power completely and the check engine light illuminated. A diagnostic scan revealed code P0303 — indicating a misfire in cylinder #3. I inspected the spark plugs, ignition wires, and coil pack, all of which appeared to be in good condition. A compression test showed 150 psi for cylinders 1, 2, and 4, but only 90 psi for cylinder 3. Additionally, there is noticeable moisture buildup in the intake manifold. I'm looking for guidance on what steps to take next without removing major engine components. My husband has a 99 Toyota SR5 with a 2.7L engine and similar mileage — it's also exhibiting the same symptoms: P0303 code, cylinder #3 showing only 60 psi compression (while others read 180 psi). The vehicle remains drivable in his case. Any insights or recommended diagnostics would be greatly appreciated. Kay

Related fault codes
P0303
Comments (4)
Anonymous 2011-07-06 17:37

Low cylinder compression like this is a serious issue. A leak-down test should be performed first to identify whether the problem lies in valve sealing, piston rings, or cylinder head integrity — removing the head isn't necessary unless the leak-down confirms internal damage.

Anonymous 2011-07-07 08:19

A leak-down test is a more targeted diagnostic than full engine disassembly. It can help pinpoint whether the issue is due to worn valves, valve seals, or piston ring failure in cylinder #3.

Anonymous 2011-07-08 19:11

I recommend starting with a leak-down test to determine the root cause before considering head removal. A broken valve spring is unlikely without visible symptoms — this test will help rule out or confirm internal engine issues.

Anonymous 2011-07-18 11:30

Thanks for the helpful suggestions — I'll pass them on to my husband's mechanic for further evaluation.