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1997 Jeep Laredo 97 laredo P0306

Tiny
MIKEGROSS12
  • MEMBER
  • 1997 JEEP GRAND CHEROKEE LAREDO
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 170,000 MILES
Got this code p0306. Auto zone says (misfire #6 cyl.). 1 plugs & or wires.2-vacume.3-injector.4-fuel pressure. Heres what happened. Power steering went the old lady continued to drive home, now its overheating. Changed power steering pump &all fluids. Everythings fine.30 miles later runs terrible (mainly idleing). Now at warming the vehicle up I notice black exaust deposits on the ground. I also here a whistle or whine at fast acceleration but not at idle. Cant find vacume leak. Any suggestions
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Tuesday, February 3rd, 2009 AT 10:07 AM

13 Replies

Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
First I would work on what is causing the 6th cyl to miss fire. Have you pulled the plug from it to see what it looks like? How does the Dist. Cap and rotor look? Let me know what you can and we will take it from there.
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Tuesday, February 3rd, 2009 AT 10:18 AM
Tiny
MIKEGROSS12
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Never pulled plug. Probly wont get to it till this weekened. Let you know asap. Thanks
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Tuesday, February 3rd, 2009 AT 10:34 AM
Tiny
MIKEGROSS12
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  • 11 POSTS
I pulled #6 plug plus 2 others. They all have a carbon like build up on all of them. Looked at rotor and cap no carbon build up and couldnt see no cracks. What do you suggest
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Tuesday, February 3rd, 2009 AT 12:19 PM
Tiny
MIKEGROSS12
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Do I need to donate every time to get an answer. Pulled plugs dry carbon deposit on 3 plugs(only pulled 3). Cap & rotor look good
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Wednesday, February 4th, 2009 AT 8:50 AM
Tiny
RACEFAN966
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No you do not need to donate for every question This is a part time job for me and my best times of answering are in the morning and evening but sometimes I spend time with the family so I don't get to it in the evenings.
Anyway I would replace all the spark plugs and get a gapper and gap them to speck and put in new plugs all 6. I would also say you should run some seafoam through the gas tank with a tank of gas. Is this jeep used mostly for short trip driving? Get back to me and we go from there.
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Wednesday, February 4th, 2009 AT 10:32 AM
Tiny
MIKEGROSS12
  • MEMBER
  • 11 POSTS
Jeep does a lot of in town running but also gets on the highway quite a bit. Now that its cold the ol lady does alot of warming up & short runs? The rotor looks like a burn mark on the underside edge of the contact. Put lucas in the tank, dry gas, gas treament etc. About every other fill-up. Maybe plugs and lucas? Heard bad things about seafoam
thanks
mike
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Wednesday, February 4th, 2009 AT 10:52 AM
Tiny
RACEFAN966
  • MECHANIC
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Ok plugs yes I would say they are needed by your discription as for fuel treatment use what you like lucas is good too. I use Seafoam in my mustang and my F-150 and my 99 Jeep and no problems at all but brand preference is up to you do what you fee comfortable with. If you think the rotor is bad then change the cap at the same time however I would do the plugs first and see how much that improves things. As for fuel additives never use a fuel treatment with every fill up as it will glaze the plugs use it like every 3000 miles or so. Let me know how it goes and we will take it from there.
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Wednesday, February 4th, 2009 AT 9:27 PM
Tiny
MIKEGROSS12
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  • 11 POSTS
Went to get plugs now I got a code p0171 o2 sensor. Its saying running to lean but I can smell it way to rich. Really confused now?
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Thursday, February 5th, 2009 AT 11:11 AM
Tiny
RACEFAN966
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Ok have you replaced the plugs yet? If not then this could be just part of the original problem the miss is causing the engine to lean out so the O2 sensor is trying to correct for it and it will actually end up running richer.
If after the plugs this happened then I would like you to check for any vacuum leaks and ohm the spark plug wires should only be 250 to 1000 ohms per inch any more then they are bad and need to be replaced. Let me know what you find.
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Friday, February 6th, 2009 AT 10:07 AM
Tiny
MIKEGROSS12
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  • 11 POSTS
Changed plugs no difference. When driving mash the gas sounds like vacume? Dont here it idle
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Friday, February 6th, 2009 AT 12:46 PM
Tiny
RACEFAN966
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Ok what do you mean can't hear it idle? Please explain the best you can. Could ohm the plug wires? They should be no more the 1000 ohms per inch. Have you checked for any vacuum leaks in the intake system or manifold? How old is the fuel filter?
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Saturday, February 7th, 2009 AT 9:06 AM
Tiny
MIKEGROSS12
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Sounds like a vacume leak while driving & mashing the throttle but cant hear no leak in park or neutral while rev. The engine. Gotta look into the ohm situation
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Saturday, February 7th, 2009 AT 9:26 AM
Tiny
RACEFAN966
  • MECHANIC
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Ok so get a spray bottle of water and spray around the intake and the PVC orfice (as there is no actuall pcv valve) and check the air intake boot for breaks and crack that may be opening when you step on the gas. Check all vacuum lines that you can. You should hear a drop in RPM when the water hits the leak.
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Monday, February 9th, 2009 AT 10:03 AM

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