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Old 07-31-2013, 06:24 AM   #1
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Engine Pulsing

Hey Everyone,

Lately I've been noticing my 4.0L is pulsing slightly at idle. Along with this it has a slight hesitation when first shifting into gear. Other than that it runs pretty good. Here's what I've done to the jeep so far:

New Plugs
New Plug Boots
Cleaned TB
Cleaned IAC
New Cat-back Dynomax Exhaust
New Air Filter
New Fuel Pump

I don't have a CEL on, so I'm just wonder if there's any way to determine why it's pulsing. It also just passed CT emissions for what it's worth. I'm thinking an injector issue or possibly the coil pack gone bad, but I'm open to other suggestions. Maybe it's nothing? Thanks in advance for the input!

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Old 07-31-2013, 07:02 AM   #2
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When you say pulsing, do you mean the rpm's jump up and down? Or is just a sound that the motor makes?

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Old 07-31-2013, 07:19 AM   #3
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Both. I can see the tach moving up and down, albeit a small movement. But the tach movement coincides with the pulsing sound I hear. Could it be a bad idler pulley or alternator?
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Old 07-31-2013, 07:37 AM   #4
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You'd have much worse problems if your alternator was bad. To rule out your idler pulley, loosen up the tension on your serpentine belt and wiggle around the pulleys it runs on. All the wheels should spin freely without hanging up anywhere. Could just be a bad bearing in one of them. Does this pulsing go away, speed up, etc.. when you rev the engine while not moving?
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Old 07-31-2013, 08:42 AM   #5
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The pulsing is only noticed while idling at a stand still. If I hold the rpms at 1500 there's no pulse. There's also no pulse while driving. I'll have to take the belt off this weekend and check that all the pulleys are spinning free.
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Old 07-31-2013, 08:50 AM   #6
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It doesn't sound like a hung up pulley though. My first guess would be the IAC, but you said you cleaned that. Did you pull back the sleeve and clean it with carb cleaner when you did it?
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Old 07-31-2013, 09:31 AM   #7
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Sure did.
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Old 07-31-2013, 09:37 AM   #8
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Quote:
Originally Posted by apannone View Post
Hey Everyone,

Lately I've been noticing my 4.0L is pulsing slightly at idle. Along with this it has a slight hesitation when first shifting into gear. Other than that it runs pretty good. Here's what I've done to the jeep so far:

New Plugs
New Plug Boots
Cleaned TB
Cleaned IAC
New Cat-back Dynomax Exhaust
New Air Filter
New Fuel Pump

I don't have a CEL on, so I'm just wonder if there's any way to determine why it's pulsing. It also just passed CT emissions for what it's worth. I'm thinking an injector issue or possibly the coil pack gone bad, but I'm open to other suggestions. Maybe it's nothing? Thanks in advance for the input!
Is it like "idle hunting"?
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Old 07-31-2013, 09:50 AM   #9
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I'm not sure what you mean by idle hunting.
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Old 07-31-2013, 10:01 AM   #10
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Idle hunting is when the engine cannot maintain a stable idle, as if it were "hunting" for the correct.

Can you take a video and youtube since armchair diagnostics are like shotgun blasts.
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Old 07-31-2013, 10:47 AM   #11
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I'll try to upload a video or sound clip later.
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Old 07-31-2013, 10:55 AM   #12
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Kindof sounds like what mines doing. Just at idle. Small hicup. But give it any gas it's smooth as can be. Mines an auto tho. Not that it matters.
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Old 08-02-2013, 06:37 PM   #13
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Ok, sorry for the delay. Here's a link to the video/sound clip I was able to get. You'll need headphones to catch the pulsing I'm referring to.

Jeep Pulsing

Sorry if the video ends up sucking. Please let me know if you guys notice what I'm talking about or if I'm going crazy. lol

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