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Random Misfire Codes

Tiny
DSTROMBEE
  • MEMBER
  • 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 replaced the throttle position Sensor. Really getting frustrated, where do I go from here?
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Tuesday, September 3rd, 2013 AT 9:25 AM

13 Replies

Tiny
MADMIKE1735
  • MECHANIC
  • 951 POSTS
Just because you replaced a part, doesn't 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 doesn't 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....

Here is a guide that can help

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Please let us know what happens.

Cheers
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Friday, September 13th, 2013 AT 9:14 PM
Tiny
DSTROMBEE
  • MEMBER
  • 4 POSTS
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
  • 4 POSTS
Been a couple of weeks and no engine light.
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Saturday, September 21st, 2013 AT 9:08 PM
Tiny
MADMIKE1735
  • MECHANIC
  • 951 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
  • 4 POSTS
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
  • MECHANIC
  • 951 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
Tiny
STEEV127
  • MEMBER
  • 1 POST
  • 1999 JEEP GRAND CHEROKEE
  • 4.0L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 160,000 MILES
I replaced fuel injector and plugs, still missing. I replaced coil pack and wont even start.(Hits like its out of time.) Took it back and got a different new one. Same thing. Put old coil pack back on and it starts right up but still missing on #6?
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Monday, November 20th, 2017 AT 12:23 PM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Have a pro diagnose this as they are very hard to find. It will save you some money and aggravation. It can be a sensor in engine, vacuum leak low compression injector or any electrical problem like plugs wires etc.
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Monday, November 20th, 2017 AT 12:23 PM (Merged)
Tiny
SWOLLEN2004
  • MEMBER
  • 2 POSTS
  • 1999 JEEP GRAND CHEROKEE
  • 220,000 MILES
Earlier today I was driving my jeep and it ran fine. I stopped and turned my jeep off for about five minutes. I tried starting my jeep and it was rough starting and rough idling. It then through a check engine light. I took It to get the codes ran and it was throwing a cylinder 1 and 2 misfire code. I then changed the spark plugs and reset the codes. I am still having the same issue. What could cause this? My jeep has the 4.7 v8 engine.
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Monday, November 20th, 2017 AT 12:23 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Are you still getting the same code? Does your vehicle have the coils over each plug? If so, switch 1 and 2 with two known good ones to see if that makes a difference. In other words, does the misfire change to the other cylinders. You may also want to check both cylinders for compression. There could be a valve or head gasket issue.
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Monday, November 20th, 2017 AT 12:23 PM (Merged)
Tiny
SWOLLEN2004
  • MEMBER
  • 2 POSTS
I am getting the same codes even after coil swap. Cylinders have good compression.
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Monday, November 20th, 2017 AT 12:23 PM (Merged)
Tiny
EAGLE7491
  • MEMBER
  • 1 POST
  • 2004 JEEP GRAND CHEROKEE
  • 4.0L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 163,000 MILES
Had a steady persistent misfire in number 2 cylinder. Replace #2 fuel injector, spark plugs, coil pack and TPS sensor. Nothing has helped. What's the next step?
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Monday, November 20th, 2017 AT 12:24 PM (Merged)
Tiny
CARADIODOC
  • MECHANIC
  • 33,916 POSTS
Compression test, valve problem. Swap the injector with one from a different cylinder, and the spark plug with one from yet another cylinder, erase the fault codes, then see if a misfire code sets for a different cylinder or the same one.
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Monday, November 20th, 2017 AT 12:24 PM (Merged)

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