Engine power decreases on the highway - JeepForum.com
 
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post #1 of 11 Old 02-06-2015, 03:38 PM Thread Starter
cwebb
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Engine power decreases on the highway

Hi everyone,

Hoping you guys can help me out. On my way home today I turned onto the highway and began accelerating. As soon as I get to around 40mph the car stops accelerating. The speedometer thinks it is still accelerating and keeps climbing up to 70 mph if I keep my foot on the accelerator. Engine rpms increase as well. Everything seems normal except that fact that the jeep still is going 40 mph when it should be at 60+. Any suggestion? Its a 2002 6L Manual TJ Wrangler.

At lower speeds everything is fine. But as soon as I get to around 40mph the issue occurs.

Thank you for any advice!!!

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post #2 of 11 Old 02-06-2015, 04:20 PM
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Have you checked your transmission fluid? Any error codes?

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post #3 of 11 Old 02-06-2015, 05:04 PM Thread Starter
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Originally Posted by NHfireLJ View Post
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Have you checked your transmission fluid? Any error codes?
No error codes and transmission fluid is full.
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post #4 of 11 Old 02-06-2015, 05:10 PM
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No error codes and transmission fluid is full.
You say its a 5 speed? How's your clutch doing?

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post #5 of 11 Old 02-06-2015, 06:02 PM
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How do you know what speed you're actually going then? Did you use a gps to make sure determine your actual speed?

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post #6 of 11 Old 02-06-2015, 06:08 PM Thread Starter
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Originally Posted by frenchy206 View Post
How do you know what speed you're actually going then? Did you use a gps to make sure determine your actual speed?
Yes after I was pretty obviously going slow I powered up the gps. I was topping at about 40mph but speedo read 70mph...could it be fuel pump or the CATs?
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post #7 of 11 Old 02-06-2015, 09:59 PM
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No. Usually a fuel pump goes out completely. Cats would restrict power. It sounds like a drivetrain issue, such as clutch.

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post #8 of 11 Old 02-06-2015, 10:13 PM
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Quote:
Originally Posted by frenchy206 View Post
No. Usually a fuel pump goes out completely.
Fuel pumps can have several levels of failures. Pressure, volume, check valve.
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Originally Posted by frenchy206 View Post
It sounds like a drivetrain issue, such as clutch.
How could it be a clutch issue when the speedometer is driven by the transfer case output shaft?...

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post #9 of 11 Old 02-06-2015, 10:53 PM
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Originally Posted by Knuckelhead View Post
Fuel pumps can have several levels of failures. Pressure, volume, check valve.

How could it be a clutch issue when the speedometer is driven by the transfer case output shaft?...
Fuel pumps can fail as you described above, however most that I have seen fail, either work or don't.

You are correct. I forgot that the speedometer is driven by the transfer case output shaft.

So...what could be the problem?

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post #10 of 11 Old 02-06-2015, 11:25 PM
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Originally Posted by frenchy206 View Post
Fuel pumps can fail as you described above, however most that I have seen fail, either work or don't.
The most common failure on the TJ fuel pump is failure to maintain pressure when the engine has been at rest for a period of time. The multiple key on, key off and key on to repressurise the fuel rail comes into to play.
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Originally Posted by frenchy206 View Post
You are correct. I forgot that the speedometer is driven by the transfer case output shaft.
So...what could be the problem?
More information from the OP would be needed... IMO

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post #11 of 11 Old 02-10-2015, 09:11 AM
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Any chance you recently did anything with your speedometer gear? If for example you removed it and replaced it, or put it back in without the proper alignment, the teeth could be slipping at higher speeds. I'm not an expert but I believe this is an input into your transmission and could cause wierd shifting or other problems.
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engine , engine performance , fuel pump , power loss , spark plug

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