Question about 2000 Buick LeSabre

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Random Cylinder Misfire

I have a 2000 Buick LaSabre that suddenly started not running well.  The Service Engine Soon light often starts blinking, and stays steadily on at other times.  I went to AutoZone and they read the trouble codes that say that the system is detecting "random cylinder misfires".
The thing is that just a month or two ago I was having similar engine trouble, though the diagnostic then was stating that a specific cylinder was misfiring.  I changed all the spark-plugs, since my mileage is over 100,000.  However all the old plugs looked really good.  Unfortunately, the problem persisted, so I changed the wires.  Then the problem was solved.  (I did find that the coil connector side of the wire for the diagnosed misfiring cylinder was charred.  So I'm sure that was the real problem.  Though I have concern over what damage may have been inflicted upon the coil and/or the Ignition Control Module.)
So I know that my spark-plugs are new, and so are my wires.  What would help me in further diagnosing this issue would be to know how the system determines misfires, and whether it would report a "random" cylinder misfire if a pair of cylinders were misfiring---specifically if the pair of cylinders driven by a single coil (of the three on this vehicle) were misfiring?
Does the system determine such misfires through a detection of the ignition impulse sent to the spark-plug (back EMF, current, etc.), or does it have some ignition sensor within the cylinder (detecting light, heat, sound, whatever)?  The answer to this question will help direct my diagnosis.
If the system does not have the ability to identify a pair of misfiring cylinders, but will provide the "random" misfire code even for a pair of misfiring cylinders driven by the same ignition coil, then I could rightly suspect a coil.  Otherwise, I don't suspect a coil since this would require multiple coils to be acting up.  (Not impossible, but not so likely.)
The thing is that the sound of the engine doesn't suggest "random" misfires.  It sounds quite regular, even though the gas mileage I'm getting suggests I'm running on only four of my six cylinders.
Please help.

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  • Halliday Jul 09, 2008


        One of the things I'm trying to avoid is the very "replace until you hit it" scenario you appear to advise here.  Besides, unless the misfires are on paired cylinders, a coil "pack" (a single coil for a cylinder pair) is not going to be it---more than one coil "pack" would have to be out.  (Of course you may be referring to all three coils as a "coil pack".  That's why I've placed my use of the term "pack" in quotes.)

    A more likely scenario, to my mind, if the misfires are not on paired cylinders, would be the single Ignition Control Module that drives all three coil "packs".  (Probably not cheep either, but at least there are diagnostic tests that can be run on it before simply replacing it.)

    Thanks anyway.  (The coil "pack" idea was the first thing out of the mouth of the salesman at AutoZone, as well.)



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The problem is the ignition control module such is under the coil packs. It seems to be an internal problem in the design. I have seen it many times and if you don't belive as many will not. So disconnect the modules electrical connector and just let it sit for two to three days. After that clean ir replace your sparkplugs, they will be fails up dew to it running lean and rich. Plug it in. Plug it in and wala its fixed $ but only for a week or two then back to the same thing so in short change the ignition module and save time and money, and don't forget to thank your friendly neighbor hood mexican mechanic.

Posted on Sep 10, 2011

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I have a 2002 Buick Lesabre that began running rough about two days ago. My first repairs were the easy maintenance items. Plugs (well not so easy), plug wires, and a fuel filter. I also replaced the front motor mount which was in need of replacing. It this point I was into a guessing game so I first took the car to the local Auto parts store to find out the problem was random misfiring. Not very specific. I then went to my tire store that also does automotive work and they ran more detail diagnostics (cost $35). The answer there was the coil ignition system. My first try was to purchase one coil (there are 3 separate coils) and try each spot. No improvement. The next thing in the flow of ignition is the Ignition Control Module. They cost about $140 but are easy to replace if you are capable of doing things like replacing spark plugs. You have to remove the three coils, a fairly simple unplug and plug, and put the coils back on. Be careful not to confuse the plug wires. Cars runs as good as new.

Posted on Mar 11, 2010

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The next thing to replace is the coil packs,and 9 times out of 10,that solves the misfire.If the coilpacks don't solve the misfire,next on the list are the injectors.After that,you would pretty much be looking at an internal engine problem,as in a valve or valves not sealing or burnt,piston rings,and i have even seen a Ford 3.8ltr V6 that had a misfire that ended up being a bent connecting rod,but that is rare.Just go with replacing the coil packs,and that will likely solve your misfire.

Posted on Jul 09, 2008

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If misfire is on one bank (cyliner 1,3,5 only) then it may be O2 sensor.

Posted on Feb 02, 2009

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I had the same issues with my 02 Grand Prix GT 3.8, my problem ended up being a collapsed cat is common, have that checked ASAP.

Posted on Jan 04, 2009

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Take the coils off and also check the ignition control module.
Your local auto parts store will do an electrical check on them for free.

Posted on Sep 13, 2008

Im having the same problem with a 96 buick century. I wondering if its the coil packs. The plugs and wires have 8000miles of use. So i think it shouldnt be them. But same symptoms, engine code P0300.

Posted on Aug 12, 2008

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SOURCE: Random Cylinder Misfire

Get a Haynes manual for your vehicle and use the troubleshooting guide there.  about $20 from amazon, auto parts store or  This WILL save you time and shortcut this and any future diagnosis. Haynes IMHO are top notch and I like them better than some factory service manuals that fgo for $100 and more.

David, 99 Saturn,  Cam position sensor codes seem to indicate a engine timing (not spark, but crankshaft/camshaft sync).  Old timing belts or worn tensioners can cause belts to jump a tooth or two which can have a pretty dramatic effect.  The belt could also be old/dryrot and have lost a tooth or two causing it to jump.  If any of these are the case, or if the timing belt interval is near,  replace timing belt, tensioner, idler roller if present and water pump.  FYI, quality OEM ignition wires shold last at least 10 years.  If they are really bad, you can open the engine compartment on a dark night and you will see sparks arcing between them and/or something metal nearby.  We all replace wires when we are not sure what the problem is, and regardless of what anyone tells you, it only rarely solves anything unless the car is more than 10 years old. 

good luck.

Posted on Oct 30, 2008

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