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Old 03-22-2013, 08:43 PM
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Running rough in 4th at low RPM

I have a 2005 GC Limited 5.7l hemi with 80k on it, I had it from new. While driving at 30-35 in town it shifts into 4th gear and is usually at 1200-1400 RPM. It is running really rough at this speed and RPM only in 4th. I can really notice it if I have a slight incline in the road. Shifting to 3rd brings up the RPM and it stops running rough. Applying light throttle it is very sluggish and get rougher. No CEL light, no codes and the rest of the time it runs fine. Plugs were changed at about 65K, plug wires have never been replaced. I have run Seafoam through the throttle body, Clean as much of the throttle body without taking it off and run a can of Seafoam in a couple of full tank of Gas. Any ideas of the cause?

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nwcanuck
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Old 03-23-2013, 01:21 PM
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Re: Running rough in 4th at low RPM

First, welcome to the forum.

I'd recommend you first check the resistance of the spark plug wires. If they haven't been changed in 80K, there is a pretty good chance one or more are going bad. The old "rule of thumb" is, no more than ~10,000 ohms per foot of wire, but they should be quite a bit less. To give you an idea, I still have the original wires off my 05 Hemi LX (~20K on them) and one wire, about 3 ft. long reads ~12,000 ohms for the whole wire. I changed over to the Taylor Shorties, and they've been fine, plus it gets rid of the "rats nest" over the top of the engine.

Also, what kind of plugs did you put in it? Some of the early Hemi's don't like anything but copper core plugs. Others don't seem to have a problem.
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Old 03-23-2013, 09:00 PM
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Re: Running rough in 4th at low RPM

Quote:
Originally Posted by jeepgcoman View Post
First, welcome to the forum.

I'd recommend you first check the resistance of the spark plug wires. If they haven't been changed in 80K, there is a pretty good chance one or more are going bad. The old "rule of thumb" is, no more than ~10,000 ohms per foot of wire, but they should be quite a bit less. To give you an idea, I still have the original wires off my 05 Hemi LX (~20K on them) and one wire, about 3 ft. long reads ~12,000 ohms for the whole wire. I changed over to the Taylor Shorties, and they've been fine, plus it gets rid of the "rats nest" over the top of the engine.

Also, what kind of plugs did you put in it? Some of the early Hemi's don't like anything but copper core plugs. Others don't seem to have a problem.
Can't remember what plugs I put in, I got them from the dealer. I was thinking wires might be the issue, what's puzzling me is the fact that it only has the issues at ~1200-1700 RPM. I'll check the wires and go from there.

Thanks
nwcannuck
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