Bucking!

tiedyed8 · 03-29-2006, 10:48 AM

I have searched the forum--so please dont tell me to go do a search. I just replaced my TPS-due to not being able to adjust correctly--could not get it to change readings on the meter. New TPS, adjusted with a meter--runs much better. BUT--now I am having a weird problem. NO more hesitations at take off, idle is normal, not thru the roof--here is the catch. When cold--it will buck pretty bad on me. Here is the weird part--it will not do it if I am accelerating, or if I let off the gas completely--it only does it when you get to a cruising speed--where you are not accelerating or decelerating. It does it at high speed and low speed. If I press pedal, the bucking goes away. The other weird thing is that the RPM's never change. At first I thought it might be the trans slipping--but RPM's are constant, even during the bucking episodes. After driving for a little while and once warmed up good--it goes away. Any help would be greatly appreciated. Thanx!!!

stam89xj · 03-29-2006, 07:59 PM

might be the egr valve.

90turbo1 · 03-29-2006, 10:59 PM

my 88 4.0L does the exact same thing to me.....

changed the TPS, O2, IAT, air filter, PCV system, plugs, wires, cap, rotor, checked timing,

noticed that the Idle speed control motor was very dirty so I cleaned it. nothing changed, the only thing I can do to make the bucking stop is to adjust the TPS higher than needed, like. .88 V

the bucking is still there but it seems to move to other parts of the rev range...

mine bucks around while cruising at 60 on interstate it gets really bad.

let me know what you find wrong

tiedyed8 · 03-29-2006, 11:59 PM

Here is a list of all of the things I have changed. Fuel filter and pump. IAC, TPS, O2 sensor, air filter and plugs, thermostat and temp sending unit. All of these are not related to bucking--the 88 chief is new to me, so I am going thru and fixing/replacing as I can. I will keep checking--will check EGR tomorrow. Any other suggestions would be appreciated. I will post if I find the fix. Thanks

90turbo1 · 03-30-2006, 09:37 PM

anyone have any input on this???????

just checking

also was wondering if the other two that have this problem, are your rear main seals leaking like mine is???

was thinking that the oil and dirt may have coated the crank sensor making it not read correctly

just a thought

90turbo1 · 03-31-2006, 06:10 PM

hope this helps everyone.

talked to a guy that was fixing jeeps for about 20 years now, he is very familiar with this problem of the bucking XJ.

first of all he asked me the questions:

does it do the bucking just off idle when leaving a stop sign or such, my answer yes

does it do the bucking at steady cruising speeds on freeway? I said yes it does it around 60 MPH or when the load on engine seems to change a bit.

he said there is a TSB for this problem it is involving the distributer and play that occurs in the rotor assy. Basically the distributer gets play in it causing the rotor to be further away from the terminal than it should be, this in turn causes the electricity to go from the rotor to another terminal on the cylinder that doesnt need it causing a missfire or a slight backfire or a bucking...

to correct this you need to measure the distance from the rotor tip to the electrode in the cap. and you can slightly adjust the distributer if you remove a clip or something. I am waiting for him to give me a copy of the TSB so I can perform it to my jeep

I will keep you posted when I am done

SanDiegoXJ · 03-31-2006, 07:31 PM

Weeeeee!

I think you nailed my mystery problem!!!! :happpyd:

Please post the TSB so I can try it too.

Cheers!

tiedyed8 · 04-01-2006, 12:00 AM

Hey guys--I was doing some research today and ran across this. I dont know if it will work, but I will try it tomorrow. Maybe this will help somebody.(Hopefully me!!!) See the attachment.

tiedyed8 · 04-03-2006, 08:20 AM

I dont know if anybody else tried this--but my bucking is completely gone!!!!

I still have a little hesitation at take off when cold, but seems to get some better when warm--proly needs a tune-up. BUT--my major problem was fixed with the computer re-learn procedure from the FSM. Hope this will help someone else! OH--I actually did it 2x's--but I'm good now!!!!!!

03-29-2006, 10:48 AM	#1
tiedyed8 Registered Join Date: Jan 2006 Location: Macon, GA Posts: 46 Thanks: 0 Thanked 0 Times in 0 Posts	Bucking! I have searched the forum--so please dont tell me to go do a search. I just replaced my TPS-due to not being able to adjust correctly--could not get it to change readings on the meter. New TPS, adjusted with a meter--runs much better. BUT--now I am having a weird problem. NO more hesitations at take off, idle is normal, not thru the roof--here is the catch. When cold--it will buck pretty bad on me. Here is the weird part--it will not do it if I am accelerating, or if I let off the gas completely--it only does it when you get to a cruising speed--where you are not accelerating or decelerating. It does it at high speed and low speed. If I press pedal, the bucking goes away. The other weird thing is that the RPM's never change. At first I thought it might be the trans slipping--but RPM's are constant, even during the bucking episodes. After driving for a little while and once warmed up good--it goes away. Any help would be greatly appreciated. Thanx!!! __________________ 88 Cherokee Chief 4.0L Stock now, but new project :nuts: :jammin:

03-29-2006, 10:59 PM	#3
90turbo1 Registered Join Date: Dec 2005 Location: Spokane, WA Posts: 246 Thanks: 0 Thanked 0 Times in 0 Posts	my 88 4.0L does the exact same thing to me..... changed the TPS, O2, IAT, air filter, PCV system, plugs, wires, cap, rotor, checked timing, noticed that the Idle speed control motor was very dirty so I cleaned it. nothing changed, the only thing I can do to make the bucking stop is to adjust the TPS higher than needed, like. .88 V the bucking is still there but it seems to move to other parts of the rev range... mine bucks around while cruising at 60 on interstate it gets really bad. let me know what you find wrong __________________ Larry Pengilly BMW Master Technician 1988 Jeep Cherokee 4.0L 1998 Ford F-150 1996 Nissan 240sx SE

03-29-2006, 11:59 PM	#4
tiedyed8 Registered Join Date: Jan 2006 Location: Macon, GA Posts: 46 Thanks: 0 Thanked 0 Times in 0 Posts	Here is a list of all of the things I have changed. Fuel filter and pump. IAC, TPS, O2 sensor, air filter and plugs, thermostat and temp sending unit. All of these are not related to bucking--the 88 chief is new to me, so I am going thru and fixing/replacing as I can. I will keep checking--will check EGR tomorrow. Any other suggestions would be appreciated. I will post if I find the fix. Thanks __________________ 88 Cherokee Chief 4.0L Stock now, but new project :nuts: :jammin:

03-30-2006, 09:37 PM	#5
90turbo1 Registered Join Date: Dec 2005 Location: Spokane, WA Posts: 246 Thanks: 0 Thanked 0 Times in 0 Posts	anyone have any input on this??????? just checking also was wondering if the other two that have this problem, are your rear main seals leaking like mine is??? was thinking that the oil and dirt may have coated the crank sensor making it not read correctly just a thought __________________ Larry Pengilly BMW Master Technician 1988 Jeep Cherokee 4.0L 1998 Ford F-150 1996 Nissan 240sx SE

03-31-2006, 06:10 PM	#6
90turbo1 Registered Join Date: Dec 2005 Location: Spokane, WA Posts: 246 Thanks: 0 Thanked 0 Times in 0 Posts	hope this helps everyone. talked to a guy that was fixing jeeps for about 20 years now, he is very familiar with this problem of the bucking XJ. first of all he asked me the questions: does it do the bucking just off idle when leaving a stop sign or such, my answer yes does it do the bucking at steady cruising speeds on freeway? I said yes it does it around 60 MPH or when the load on engine seems to change a bit. he said there is a TSB for this problem it is involving the distributer and play that occurs in the rotor assy. Basically the distributer gets play in it causing the rotor to be further away from the terminal than it should be, this in turn causes the electricity to go from the rotor to another terminal on the cylinder that doesnt need it causing a missfire or a slight backfire or a bucking... to correct this you need to measure the distance from the rotor tip to the electrode in the cap. and you can slightly adjust the distributer if you remove a clip or something. I am waiting for him to give me a copy of the TSB so I can perform it to my jeep I will keep you posted when I am done __________________ Larry Pengilly BMW Master Technician 1988 Jeep Cherokee 4.0L 1998 Ford F-150 1996 Nissan 240sx SE

03-29-2006, 07:59 PM	#2
stam89xj Registered Join Date: Dec 2002 Location: aston,pa Posts: 4,972 Thanks: 0 Thanked 2 Times in 2 Posts	might be the egr valve.

03-31-2006, 07:31 PM	#7
SanDiegoXJ Registered Join Date: Feb 2006 Posts: 192 Thanks: 0 Thanked 0 Times in 0 Posts	Weeeeee! I think you nailed my mystery problem!!!! :happpyd: Please post the TSB so I can try it too. Cheers!

04-03-2006, 08:20 AM	#9
tiedyed8 Registered Join Date: Jan 2006 Location: Macon, GA Posts: 46 Thanks: 0 Thanked 0 Times in 0 Posts	I dont know if anybody else tried this--but my bucking is completely gone!!!! I still have a little hesitation at take off when cold, but seems to get some better when warm--proly needs a tune-up. BUT--my major problem was fixed with the computer re-learn procedure from the FSM. Hope this will help someone else! OH--I actually did it 2x's--but I'm good now!!!!!! __________________ 88 Cherokee Chief 4.0L Stock now, but new project :nuts: :jammin:

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