2003 JEEP GRAND CHEROKEE RANDOM MISFIRE CODES

  • Tiny
  • dstrombee
  • 2003 Jeep Grand Cherokee
  • 48,500 miles

I have a 2003 Jeep Grand Cherokee Laredo. Inline 4.0 6-Cylinder. I keep getting the following codes:

P0300: Random/Multiple Cylinder 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

Sometimes I only get the PO300 Random misfire.

One time I got P0352: Ignition Coil "B" Primary/Secondary Circuit

The car will run rough and lose power. I reset the codes and it runs fine. I have replaced the Camshaft Position Sensor, The Crankshaft Position Sensor, The Ignition Coils, and the Spark Plugs. On an unrelated issue I rplaced the throttle position Sensor. Really gettin frustrated, where do I go from here?

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Tuesday, September 3rd, 2013 AT 9:25 AM

8 Replies

  • Tiny
  • hmac300
  • Expert
  • 43,674 posts

Have a pro check this because these are hard to diagnose and can be a multitude of things if not basic like plugs or wires. It can be anything from a vacuum leak, a sensor or injector or something else causing it.

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Tuesday, September 3rd, 2013 AT 12:28 PM
  • Tiny
  • madmike1735
  • Expert
  • 963 posts

Just because you replaced a part, doesnt mean it is good. I had this happen to me the other day in our shop. Replaced a coil pack, and problem persists! Tested, and verified the new coil pack was bad! Its annoying as heck. But I would try another coil pack. If that doesnt fix it, then your looking at further diag from your PCM to the coil pack. Its possible your pcm may be bad. Its rare, so go with the most common.

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Friday, September 13th, 2013 AT 9:14 PM
  • Tiny
  • madmike1735
  • Expert
  • 963 posts

Just wondering if this problem has been resolved?

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Saturday, September 21st, 2013 AT 7:54 PM
  • Tiny
  • dstrombee
  • Member

Problem has been resolved and not by any method I would have guessed. 1st, Jeep has only 44,000 miles on it. A treatment with Seafoam through the air intake, vacuum line and in the oil did the trick. A lot of new parts were put on the Jeep for what could have been solved with $10 of Seafoam. I never would have guessed carbon build up could have caused such a headache on a car with 44,000 miles.

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Saturday, September 21st, 2013 AT 9:06 PM
  • Tiny
  • dstrombee
  • Member

Been a couple of weeks and no engine light.

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Saturday, September 21st, 2013 AT 9:08 PM
  • Tiny
  • madmike1735
  • Expert
  • 963 posts

Im very glad to see that you have resolved this. The carbon that built up may have been because of numerous causes. Does this smoke when you start it up? Its possible oil is leaking from the valve seals, and building up. For it to be so bad to cause such a multiple misfire in 5 out of 6 cylinders is rare.

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Tuesday, October 1st, 2013 AT 6:23 PM
  • Tiny
  • dstrombee
  • Member

Jeep coded again yesterday with the same codes as original problem. First time since 9/12/13 when I did the SeaFoam treatment. Prior to 9/12, I could get it to code, regularly like clockwork in 42 minutes of in town driving. Since 9/12, I have driven Jeep for hours without a probem, until yesterday after about 1 and 1/2 hour of driving. Jeep does not smoke, oil levels do not drop between oil changes, so, I don't think oil leaking from valve seals. Have just completed another SeaFoam treatment. Going on a 400 mile trip tomorrow. Will see how it goes. How can carbon build up so fast? Using Mobil gasoline.

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Saturday, October 19th, 2013 AT 12:07 PM
  • Tiny
  • madmike1735
  • Expert
  • 963 posts

Its not that carbon builds up fast. Any of those chemicals just dont work as well as they are made out to. All the original codes came back? Misfire cyl 2 through 6? How does this thing run? For a misfire to set a code, it should be noticeable in driveability. The coil pack unit on these fail commonly. More when the engine gets up to running temp. This is what I want you to do. Disconnect your battery. Both cables. Touch both cables together for 30 seconds. Reset all your keep alive memory, and start fresh. Drive it for a bit. See what codes come back. And pay attention to how it runs. Any bucking, misfires, lack of power. We will start all over. This way I can make sure we get it right.

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Saturday, October 19th, 2013 AT 6:09 PM

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