bucking in that 45 - 50mph range after tuneup - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 06-29-2013, 06:28 PM   #1
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Default bucking in that 45 - 50mph range after tuneup

Hi,
I am new and have a question,I tuned up my 2002 Buick lassabre last week, I replaced the spark plugs but didn't get to do the wires at that time. The car went to New Hampshire (124 miles away)I didn't drive it, Once on the highway it started to buck at 45 - 50 mph then was ok before and after 50 or so mph. but continued to buck in that 45 - 50 range. The driver took the car to a garage and they worked on it and told her (yes"her" dont ask) That it had 2 cracked plugs and 3 bad wires. I know I cracked the old middle plug in the back side of the engine when I removed it but was extra careful with installing the new plugs because of breaking the old one. My question is Could the car run fine up to 45mph and fine after 50mph on a 2 hour trip with 2 cracked plugs and 3 bad wires? I think not but the that'* why I am posting for your thoughts... I think they garage mechanic she stopped at cracked the plugs.
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Old 06-29-2013, 10:00 PM   #2
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Yup, that'* the weird thing about these 3800'*. Right around 45MPH, you are in 4th gear and your torque convert locks up. This is technically 5th gear. So, now your engine is lugging at the low 1700ish RPM range. When this much load is on the engine at such a low RPM and you have bad ignition parts, misfires and "bucking" occurs.

So yea, the shop was probably correct in the wires being bad. Unfortunately, wires tend to get brittle on the inside after a couple years and when you start pulling them off of plugs to replace the plugs, they break.
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Old 06-29-2013, 11:48 PM   #3
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I would think the check engine light would be on.....can this go on and the CEL not be on...??
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Old 06-30-2013, 08:36 AM   #4
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most of the time you wont get a misfire code for plug/wires unless they are really bad
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Old 06-30-2013, 09:23 AM   #5
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I would think the check engine light would be on.....can this go on and the CEL not be on...??
I wouldn't be surprised if you have a PENDING misfire code.
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Old 07-02-2013, 02:29 PM   #6
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OK thanks for the replies, I knew I didn't break the plugs installing them.
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Old 07-02-2013, 07:56 PM   #7
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OK thanks for the replies, I knew I didn't break the plugs installing them.
I say if in doubt, take them back out.
Before I knew exact plug torque specs, and before I had a torque wrench, I overtightened a plug, somehow cracking the ceramic part, which I am pretty sure gave me a bit of a miss, I cannot remember if it set any misfire codes though, as this was many years back.

Torque info below taken from AllData.

Tighten Spark plugs to 15 Nm (11 lb. ft.) . NOTE : On the 3800 engine, aluminum heat shields are used over the spark plug boots on cylinders which are close to exhaust tubing. Care should he taken to ensure these heat shields are fully seated.
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Old 07-02-2013, 08:01 PM   #8
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I had an issue like that a couple years ago. After the complete tuneup, I immediately had a misfire on #1(verified by scantool). Removed it, and found a long crack in the ceramic. Replaced it, misfire gone.
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