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Autozombie
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Oct 15, 2011, 5:41 AM
Post #1 of 7
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1998 jeep grand Cherokee
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It is a 4l straight 6 and I am getting a p302 code #2 misfire.
I have gave it a tune up and have checked for spark and checked the injector harness with a node and have swapped injectors Around still have the same problem. Ok I have did a vacuum test it read 15 psi wIth very little movement on the needle almost can't see it. Also have did a coolant system pressure check started at 15 psi and over about 20 min or so it went down to 12 psi. Also checked pressure when it was running when engine was warm it started to raise pressure in the coolent system very slowly . So my next question is could a blown head gasket cause a misfire also is the any definitive way to check to be sure the head gasket is bad?
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re-tired
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/ Moderator
Oct 15, 2011, 6:47 AM
Post #2 of 7
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Re: 1998 jeep grand Cherokee
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First of all its great that your doing some some tests on your own. Let me touch on a few technical items . When checking vac your not looking for pressure (PSI) your looking for vacumm (HG).The reading you got was good, steady means no valve problems. Another vac related test is to have egine at idle , spray some carb cleaner using a small straw at intake mainifold and at vac lines. Listen for change in rpm .When checking cooling system, you want to put tester on eng cold , pump up the pressure till its at the pressure stamped on the cap and see if it holds approx 15 min. To check for head seepage, remove plugs, pump up coolant press as before. After 15 min crank eng over and watch for water vapor out of plug holes. To be absolutly sure , rent a combustion gas tester and follow directions,,,,,,,,,,,,,
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LIFE'S SHORT GO FISH
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Sidom
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Oct 15, 2011, 5:26 PM
Post #3 of 7
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Re: 1998 jeep grand Cherokee
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15 hg is pretty low, you should be between 18 & 20 ( i'm assuming you're at sea level & not 5000 ') you should follow RT's advise & check for vacuum leaks.... Is it just missing @ idle & smooths out at higher rpms???
Also wiggle the harness on # 2 & at the PCM and see if that makes any difference.
Please define "tune up"
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Autozombie
New User
Oct 19, 2011, 4:00 AM
Post #4 of 7
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Re: 1998 jeep grand Cherokee
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Ok tune up was cap rotor plugs wire. And cylinder 2 is missing all the time seams no matter what the engine is doing idles rough and drive rough. I checked the exaust manifold to see if it had cracked and a couple of the bolts were lose so i thought that might be the problem but after new gasket and getting it back together no exaust leak but still missing. I have done a coolent system test started at 15 psi and after 15 it only droped like 2 psi and no coolent came out of any cyclinder. Also done a compression test all cylinders were around 160-170psi except cyclinder 1 was around 110Psi did a wet comprssion test with same results. So not sure what direction I should go any help would be great thanks
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re-tired
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Oct 19, 2011, 8:56 AM
Post #5 of 7
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Re: 1998 jeep grand Cherokee
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If you have a 110 reading on #1 wet and dry vs 170 + - you have a possible valve problem on # 1 cyl. you need to remove valve cover and inspect valve train. If all ok you need to have a shop do a cyl leak down test.
LIFE'S SHORT GO FISH
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Autozombie
New User
Oct 19, 2011, 11:42 AM
Post #6 of 7
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Re: 1998 jeep grand Cherokee
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But that would not cause #2 to misfire would it?
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re-tired
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Oct 19, 2011, 2:41 PM
Post #7 of 7
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Re: 1998 jeep grand Cherokee
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Yes ,it is possible for a valve problem on a cyl to afect an adjacient cyl...........Bear in mind all have to go on is the info your giving me .Please double check your readings and your plug wires order . If all is correct ,have the leak down test done to see if there is cross cyl leakage do to valve problrm or head gasket failure between cyl's.
LIFE'S SHORT GO FISH
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