sluggish acceleration, stumbling... no codes, fuel pressure 50psi, ahhh help please! - JeepForum.com
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Unread 05-08-2014, 12:40 PM   #1
smcg3
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1999 WJ 
 
Join Date: Sep 2013
Location: Pearl River, NY - New York
Posts: 19
Unhappy sluggish acceleration, stumbling... no codes, fuel pressure 50psi, ahhh help please!

4.7L stumble on acceleration at medium throttle, and is generally sluggish and jerky under heavy throttle. Stumbling/jerking at medium throttle is beginning to get worse. Funny part is, at light throttle/cruise you don't notice anything, and the car gets normal mileage (19-21 indicated). But as soon as it is more than light throttle, there is no power, engine has to downshift twice to get any acceleration.

I checked the fuel pressure, and it is a steady 50psi at ALL throttle positions. I'm getting no codes, which suggests to me it's not a knock/O2 sensor. I pulled the throttle body off and cleaned inside, including inside the port of the sensor on the lower right hand side. I also checked tranny fluid, and it is at a normal level. I'm a bit stumped and could use some guidance.

I am figuring if it was a misfire/no fire in a cylinder, the knock/O2 sensors would say something. I'm wondering if it maybe a sensor? I've read throughout the forums that the CPS and TPS can be suspect, and they can cause these symptoms. However most of the posts I read were regarding the 6 cylinder, so I'd love some additional thoughts on the V8.

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Unread 05-08-2014, 01:36 PM   #2
smcg3
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Another thought: is it possible it's a vacuum leak? If so, where is the best place to start looking? What testing methods does everyone use? I've heard of using carb cleaner, as as well as the "smoke test".
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Unread 04-13-2015, 06:03 AM   #3
Double E
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SMCg3,

What was the resolution to this?
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Unread 04-13-2015, 06:36 AM   #4
mudpack
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Quote:
Originally Posted by Double E View Post
SMCg3, What was the resolution to this?
Yes, please.

You ask us for a service for you (advice), we'd like a service in return (tell us the answer). It's all about being a useful part of the Jeep community.
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Unread 04-14-2015, 07:24 PM   #5
smcg3
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Join Date: Sep 2013
Location: Pearl River, NY - New York
Posts: 19
Bad spark plug #6 cylinder. It threw a code implicating the #6 cylinder for something else, and I checked the spark plug as part of the testing and found it to be very worn. Checked all the others and they were quite worn as well... guess the owner before me hadn't changed them in awhile! Once I swapped the spark plugs it made a world of difference. Glad I was able to solve this one on my own!
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