bucking/hesitation issue :(

hello, all! happy thanksgiving :)))))))))

maybe someone can help me or offer suggestions.

i have a 1992 buick lesabre v6. nice car - 125,000 miles and have been told it has a very good engine. i bought it from my brother's brother-in-law. he only had it for a few years.

a few months back i experienced some misfiring/hesitation/bucking issues at seemingly random times. i took the car in and was told the ignition wires and spark plugs were badly mismatched, so they were all changed. i also had the fuel filter changed which was an original. the car ran well but have noticed the same problem, but a bit worse. as a note, it was taken to a local firestone which has done very well for me over the years.

what seems to happen is more consistent: usually when the car gets to around

40 mph, it starts to run a little rough. if i accelerate through that, it seems ok. at higher speeds, the bucking seems to come back more frequently, usually under sudden acceleration. if i accelerate very slowly and smoothly, the problem doesn't occur very often. i used to have the same problem with my last car but it seemed to be occasional bad gas.

i notice the problem much more often when in overdrive vs "regular" drive (3rd gear), so i've been driving it in regular drive. i tried different grades of gas, the trusty fuel system cleaner, etc. at lower speeds (under

40) i hardly ever have the problem only at higher speeds.

a few other notes: the car never stalls, starts immediately, and has plenty of power under acceleration. i did pull the trouble codes and i did pull a code for a faulty knock sensor. i did some research and suspect this could be at least part of the issue, but i don't know to what extent. can this part cause the problems i am having? i know it is related to controlling the spark function, so it's possible. i checked the tranny fluid and it is ever-so-slightly dark, but i don't think anything to be concerned about. the lever is fine. firestone suggested i do a fluid flush, but many folks have suggested not, since i don't know if the fluid was routinely changed in the past. all other fluids are fine (doesn't lose a drop of anything).

one final note ;) the rear brake seems to pulsate. i recently had the pads changed by a friend. i'm "assuming" that the rotor(s) may be warped and need to be turned (if that can be done). :) he said the rotor was smooth so it didn't need it, but i still wonder if it is warped.

any help would be great, and thank you! scott :))))))))))))

Reply to
Fishman
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frequently,

If you've pulled a EST/knock sensor code, it sounds like you should check into that. There are a couple things that may cause this code. The EST (electronic spark timing) module (if your car has one), the knock sensor as you've already mentioned and distributor timing. I'd check the timing first. Base timing should be a few degrees past TDC. Usually around 6-10*.

a couple things to check first. Happy Thanksgiving all!

-Bruce

Reply to
Bruce Chang

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