Misfire P0303 -thoughts? - JeepForum.com
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post #1 of 37 Old 12-22-2019, 07:39 PM Thread Starter
Green_giant71
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Misfire P0303 -thoughts?

Hi

Have a misfire in cylinder 3. Happens only when cold and not consistently. Code clears itself but comes back.

I pulled 1 and 3 (left and right) thoughts?

I switched the coils for those cylinders while I was at it and will clear the codes to see if the misfire switches to one, but the plug definitely looks like something is going on.

Thanks!

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post #2 of 37 Old 01-04-2020, 10:05 AM
Photoweborama
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You have the 4.0 I6?
Cylinder three has problems. But not what you are describing. Usually the injector goes bad due to excessive heat.

Usually after the car heats up itís has the problem.

I say this because itís fishy that itís cylinder three.

You can try replacing the fuel injector. Then buy some new heat shield and replace the shield that covers the manifolds and wrap the #3 injector..

Well, thatís what I would try, just because of the #3 cylinder..


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post #3 of 37 Old 01-10-2020, 04:31 PM Thread Starter
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This is a 4.7 v8, 150k miles

Misfire went away after I switched coils between 1 and 3 but has just now returned still on cylinder 3

It only happens when cold and sitting and goes away once the car warms up a little.

Any comment on the spark plug differences?
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post #4 of 37 Old 01-10-2020, 06:19 PM
retrvrtrainer
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How many miles on the car? The soot on the #3 plug makes me wonder about the rings. Maybe you should do a compression check. Is the intake clean?

Matt 7:7-11
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post #5 of 37 Old 01-10-2020, 07:13 PM
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Quote:
Originally Posted by Green_giant71 View Post
This is a 4.7 v8, 150k miles

Misfire went away after I switched coils between 1 and 3 but has just now returned still on cylinder 3

It only happens when cold and sitting and goes away once the car warms up a little.

Any comment on the spark plug differences?
My 4.7 did something like this. After sitting overnight, it would run a little rough on startup and sometimes a misfire code would pop up. I could clear it, and it would run like a champ all day. Next day in the morning, same thing again.

Mine had a small headgasket leak into cylinder 1. The coolant would pool on top of the piston overnight and then burn up on startup. Try and check that cylinder for coolant. I used a borescope camera. You can also use a wooden dowel or something similar like a dipstick.

* 2004 Overland 4.7 HO, IRO 3'', Billstein 4600's, BFG AT K02 245 70R17 *
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post #6 of 37 Old 01-10-2020, 07:52 PM
RevScott
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Quote:
Originally Posted by retrvrtrainer View Post
How many miles on the car? The soot on the #3 plug makes me wonder about the rings. Maybe you should do a compression check. Is the intake clean?
That soot isnt from oil... I'd check the cable to the plug... try checking it visually in the dark... throw a timing light on that cable and check if its firing at all when cold
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post #7 of 37 Old 01-12-2020, 09:46 AM Thread Starter
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These all seem good checks thanks

I’m s not eating a noticeable amount of coolant but maybe still the issue

Will report back
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post #8 of 37 Old 01-12-2020, 05:09 PM Thread Starter
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Ok I for sure have a leaky head gasket. Let it sit overnight then slipped a rolled up paper towel down in cylinder 3 and it soaked up a puddle of coolant pooled up on the piston.

So, I'm going to try this k&w sealer, don't have the dough for a head gasket job and no time for the diy, seems a little complex too
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post #9 of 37 Old 01-12-2020, 05:44 PM
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subscribing, my 02 seems to have the exact symptoms, does use some coolant in my case


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2002 GC Limited, all stock, undecided mods to come
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post #10 of 37 Old 01-12-2020, 08:22 PM Thread Starter
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I think if I tracked it close enough I would see some coolant consumption. It has been very small up until now but I think it has recently picked up, radiator is full but the reservoir is a little low.

Will let you know how the seal stuff works, last time I did it ( leak on the other Cylinder bank) it worked well and that was 8 years ago)
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post #11 of 37 Old 01-13-2020, 06:54 PM
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Quote:
Originally Posted by Green_giant71 View Post
I think if I tracked it close enough I would see some coolant consumption. It has been very small up until now but I think it has recently picked up, radiator is full but the reservoir is a little low.

Will let you know how the seal stuff works, last time I did it ( leak on the other Cylinder bank) it worked well and that was 8 years ago)
It's been running with that stuff in it for 8 years? Impressive.

I'm glad you got it figured out. I had the head gaskets replaced and the heads taken off and machined to the tune of $2000 all said and done. Runs great now though

* 2004 Overland 4.7 HO, IRO 3'', Billstein 4600's, BFG AT K02 245 70R17 *
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post #12 of 37 Old 01-13-2020, 10:09 PM Thread Starter
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Quote:
Originally Posted by SD Overland View Post
Quote:
Originally Posted by Green_giant71 View Post
I think if I tracked it close enough I would see some coolant consumption. It has been very small up until now but I think it has recently picked up, radiator is full but the reservoir is a little low.

Will let you know how the seal stuff works, last time I did it ( leak on the other Cylinder bank) it worked well and that was 8 years ago)
It's been running with that stuff in it for 8 years? [IMG class=inlineimg]/forum/images/JeepForum_2016/smilies/tango_face_surprise.png[/IMG] Impressive.

I'm glad you got it figured out. I had the head gaskets replaced and the heads taken off and machined to the tune of $2000 all said and done. Runs great now though [IMG class=inlineimg]/forum/images/JeepForum_2016/smilies/tango_face_smile_big.png[/IMG]
I should clarify, the mechanic had a potion of some sort with only water which I left in for 500 miles, then drained, new thermostat and coolant. I did have to blow out the heater core in reverse direction to clear it up but otherwise golden since then.
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post #13 of 37 Old 01-13-2020, 10:12 PM Thread Starter
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I put in the k&w today, so far so good will drive it around for maybe another day or two and see if the code comes back or not. I did bypass the heater core while this stuff is in there to keep that clean.

Have to be careful with no antifreeze since it’s below freezing right now but parking in garage till I get some coolant back in.
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post #14 of 37 Old 01-19-2020, 01:49 PM Thread Starter
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Well the K&W worked for a week but the head gasket leak came back with a vengeance today on the way up to the mountain so $180 tow later, back in the garage. At idle the exhaust is big time bubbling out the radiator cap.

So my dilemma now is:
1.) put in a set of reman heads with the valve seats fixed up
2.) Reman engine installed by a shop
3.) Dump the car

Been hoping to get this going and make it my daughters car when she starts driving in 2 years.

See long blocks about $2500 and up plus install costs, open to thoughts, I love this car, quadradrive is awesome, and will also get another grand Cherokee maybe 2015+ with the best traction system when it comes time for new car...

Thanks!
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post #15 of 37 Old 01-19-2020, 02:26 PM
v1rok
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Quote:
Originally Posted by Green_giant71 View Post
Ok I for sure have a leaky head gasket. Let it sit overnight then slipped a rolled up paper towel down in cylinder 3 and it soaked up a puddle of coolant pooled up on the piston.

So, I'm going to try this k&w sealer, don't have the dough for a head gasket job and no time for the diy, seems a little complex too
Green,

I might want to do similar test with paper towel. I have 4.7 V8 with misfiring cylinder #1, which throws P0301 code. This is intermittent. Sometimes it misfires, with engine shuddering. sometimes it does not and runs very smoothly.

I checked spark plug and tried replacing the coil. Did not help. Trying to think what else could be the problem.

For your test with the paper towel, I assume you took the spark plug out and simply pushed the rolled up paper towel down the hole? How long should it be? (The paper towel roll)

2003 v8 Overland; 2013 v6 Trailhawk
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