Jerking at high speeds....

[JMZ_INDY]

I have a 94 Jeep Cherokee Classic. 4.0 high output 6 cyl automatic. When I am driving on the highway at speeds 55-65 mph it will occassionally start to jerk. It's pretty consistent but only after it warms up. After I drive it about 10-15 minutes on the highway. I had the catalytic convertor replaced when I took it to have the muffler changed. I also had the throttle position sensor replaced just yesterday to find that it still does it but not as bad. I'm sure it will get worse as I drive it more. It seems when I drive it a lot it does it more and more but only at the high speeds. Is it possible the catalytic convertor is making it do this...they had to replace my old one with an aftermarket. ANY HELP IS GREATLY APPRECIATED.

[vamc]

94 classic? I thought they were countrys?(sp) hhmm.It would not be the cat. no matter how cheep or expencive it is.mm... When did you last replace the fuel filter? any codes? Does it feel like the engine is cutting out?Could be a sencer.mmmm

[JMZ_INDY]

Originally Posted by vamc

94 classic? I thought they were countrys?(sp) hhmm.It would not be the cat. no matter how cheep or expencive it is.mm... When did you last replace the fuel filter? any codes? Does it feel like the engine is cutting out?Could be a sencer.mmmm

I think you're right about it being a country. It was replaced about 10-15,000 miles ago according to the info from the previous owners, they took good care of the mechanicals.

[vamc]

I would start with a fuel filter and go from there. what kind of gas are you feeding it?

[JMZ_INDY]

Originally Posted by vamc

I would start with a fuel filter and go from there. what kind of gas are you feeding it?

Replace the filter again ? When I took it to be service they said I didn't need one. I am feeding it regular unleaded from BP.

[vamc]

BP? eeeeeee.......Dont use bp, i had nothing but problem with that co. Everybody that i know had problems from sever hesatation to there engines sutting down. The problem that i had was sever hesatation and a little knocking sound.

[oljeeptek]

Don't get off on the wrong track. Fuel problems usually cause a surging condition, not usually a harsh/crisp jerk.

Usually, sharp jerks come from spark misfires, crossfires and the like. Look for cracked spark plugs, arcing plug wires and/or boots, cap and rotor issues etc.

Start with a poor man's scope check.. A light misting of the ignition system while idleing and see if you can make it miss or arc. That's a quick check. You could have someone else in the car to load it in gear too.

You could have an O2 sensor forcing the truck lean hot, it can surge fairly hard. You can just disconnect it/them and see if the problem goes away. Silicone contamination can shift it's reading without setting any codes.

[JMZ_INDY]

Originally Posted by oljeeptek

Don't get off on the wrong track. Fuel problems usually cause a surging condition, not usually a harsh/crisp jerk.

Usually, sharp jerks come from spark misfires, crossfires and the like. Look for cracked spark plugs, arcing plug wires and/or boots, cap and rotor issues etc.

Start with a poor man's scope check.. A light misting of the ignition system while idleing and see if you can make it miss or arc. That's a quick check. You could have someone else in the car to load it in gear too.

You could have an O2 sensor forcing the truck lean hot, it can surge fairly hard. You can just disconnect it/them and see if the problem goes away. Silicone contamination can shift it's reading without setting any codes.

Thanks for the info (not sure I understand what you mean but I appreciate it, I will have to ask my mechanic) Thue truck seems to idle a little rough. It seems to do a "hiccup" type thing when going down the highway. It's like someone is stopping the power for a 10th of a second and then kicks back on. I just cant make out if it's the tranny or the engine making the kick sound when the Jeep does it. Reminds me of what it would feel like if someone were bumping you from behind. Weird...I love this truck but it is driving me batty.

[oljeeptek]

Sorry, I meant to include misting the ignition system "with a garden hose or even a water bottle". You can even watch under the hood at night in a dark location and see if you can see any blue arcs.

[buckmyjeep]

I had the same problem with mine and it jerked between 60-70mph. Check your throttle positioning sensor and your crank positioning sensor. Also it could be your fuel pressure.

[JMZ_INDY]

Is the crank position sensor something I can replace myself ? I had the throttle position sensor replaced last month. Thanks for the help...

[JMZ_INDY]

Originally Posted by buckmyjeep

I had the same problem with mine and it jerked between 60-70mph. Check your throttle positioning sensor and your crank positioning sensor. Also it could be your fuel pressure.

Is the crank position sensor something I can replace myself ? I had the throttle position sensor replaced last month. How can I test the fuel pressure ? Thanks for the help...