P0303 Cylinder 3 Misfire

Asked by GuruBFX64 Jan 20, 2019 at 08:44 PM about the 2002 Jeep Grand Cherokee

Question type: Maintenance & Repair

I have had the P0303 cylinder 3 misfire code for at least six months. We
repaired the smaller things such as the fuel injector and spark plugs. The car
shakes and runs rough, the check engine light has been on. At times, I hear
rattling (could be catalytic converter). There was also times where my car
has died out on me while accelerating (we replaced the battery). I had a
cylinder compression test done and cylinder 3 is at 60 when it is supposed to
be at 120. Currently, my check engine light has been flashing rather than
staying intermittent. The light will flash until I start driving the vehicle and
then will become intermittent again. I am assuming that this is the catalytic
converter and that it is damaged. Could a bad catalytic converter be the
reason or be related to why I have such poor pressure in cylinder 3, or
should I not get my hopes up and prepare to replace the engine/find a new
vehicle?

5 Answers

43,910

That cylinder misfire will set the code P0303, and possibly other codes caused by the misfire. If your compression test is low, that indicates a piston or valve problem. If your have the 4.7 V8 engine, you may have a valve seat insert coming loose. If you have the 4.0 liter six, the valve or push rod may have jumped off it's rocker. The latter case is not very serious. Have an engine shop take a look.

7 people found this helpful.
10

You need to find out why the cylinder pressure is at 60 psi.A leak down test will tell toy if are the valves or the piston rings.

1 people found this helpful.
60

Did you ever get an answer to this. I have the same problem with my Cylinder 5 .... it's 65psi lower than it should be. The shop wants to charge me $1300 just to take apart and diagnose to see if the warranty company will cover anything.

5 people found this helpful.
43,910

If you have an engine warranty, contact them to get some assurance your repairs are covered. Some crooked shops lure you into a procedure they know aren't covered. And remember, tearing it down to diagnose it does not fix anything. The 4.7 engine has a high failure rate. The 4.0 six is much more reliable. I wish you the best.

2 people found this helpful.
60

That's the problem, the warranty company will not give any assurance that the repairs are covered until it's diagnosed. Which means taking the engine apart, which means $1300 in diagnosis labor.

1 people found this helpful.

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