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Unread 11-12-2008, 03:09 PM   #1
hammertech
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2003 WJ 
 
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03 WJ 4.0 Rough idle / cold knock

I have a 03 WJ 4.0L 120,000 mi. Since the weather has gotten a little cooler, my GC has started knocking/pinging slightly on cold start ups. Once the engine has gotten to 180F the knock/ping will go away. The noise is not real loud, but if the window is down or you are standing outside the jeep it is audible. I have also noticed that the idle has become rough at idle in gear and out of gear. The only thing I can compare the rough idle to is when the A/C compressor kicks in or when the radiator fan first comes on. I have just changed both of my upstream O2 sensors with no improvement.

any help would be much appreciated.

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Unread 11-12-2008, 05:18 PM   #2
elmer_fud
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When was the last time you changed the oil?
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Unread 11-12-2008, 05:34 PM   #3
xJoshxx
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that knockin and pinging on cold start more like a lift tick? got a video?

this is what mine does/did http://www.youtube.com/watch?v=Rv1RSw8V1Bo
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Unread 11-12-2008, 06:14 PM   #4
hammertech
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I changed my oil last week using 10w30. It has been doing this for roughly a month. I watched the video by xjoshxx and it sounds close to my noise but mine is more consistent. the noise in the video sounds like it varies (like dice rattling in your hand). My knock is steady with the engine speed and goes away as soon as the engine warms up. And if the speed is increased the noise becomes faint.
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Unread 11-12-2008, 06:34 PM   #5
xJoshxx
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it's a lifter tick or valve tick they call it it goes away with gas but on the rev down it ticks but not while running and idling ur 4.0L sounds like a diesel sometimes

http://www.jeepforum.com/forum/f13/amsoil-motor-flush-do-not-do-4-0l-620289/
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Unread 11-12-2008, 07:27 PM   #6
hammertech
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If i rev it in park the noise will become faint, but if i am driving it stays noisy. Tomorrow i will try and take a video of the sound, symptoms and post it.
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Unread 11-13-2008, 12:59 PM   #7
hammertech
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Ok. The Jeep was camera shy today. It mad the sound a little right before it got to normal temp. Today is also a nice 60F day. Lately it has been 50-20F.

http://www.youtube.com/watch?v=3ccimTzcbyU

I noticed a little whistle when it idled down after i reved it.

this is what the exhaust sounds like.(if that would help)

http://www.youtube.com/watch?v=oRb49ucBpkg

I tried to locate the whistle, but i could not locate it. My vac lines all look good with no cracks.
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Unread 11-14-2008, 07:29 PM   #8
hammertech
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Today I changed the plugs to champion copper core with no real improvement.
This is what my old plugs look like after 15K.
http://i260.photobucket.com/albums/i...lnut/plugs.jpg

I changed all my injector o-rings just for good measure in case there was a leak.
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Unread 11-21-2008, 09:12 AM   #9
hammertech
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Update:
Today I hooked up the jeep to a generic scan tool. Maybe someone can make heads or tails from the results. Here are the results:


Since i changed the plugs I have not seen any improvement. The only thing I have noticed is that when coasting to a stop from 40mph the engine feels like it stumbles a little. Then once stopped the jeep idles rough. (rougher in drive than in park). I have been thinking of changing the crank position sensor and cam position sensor, but I don't want to throw money away on them if they are not needed. I have read other threads pointing to these sensors, but the symptoms are not totally identical. Could a MAP sensor cause these symptoms?

Does anyone have any ideas?
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Unread 11-26-2008, 12:48 PM   #10
hammertech
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I borrowed a handheld scantool from a friend and I found some interesting things. When the engine is off I am showing 28.2 inHG on my MAP with the engine running I show 11.5 inHG and a mechanical gauge on the motor shows 15 solid. Another thing is my TPS (changed a year ago due to no voltage change when moving it) is showing 17% engine off and full throttle is only 75%. And the only other thing showing up on the scantool is bank 1 sensor 2 has a faulty heater circuit, but I have no MIL light.

For the time being after the holiday I will change the O2 downstream sensor and see what happens. I am thinking the knocking noise could be the engine running a little on the rich side.



If anyone out there has a scantool, can you please see if these readings look the same on your 4.0L. Thanks.
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