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Old 04-04-2011, 05:25 PM   #1 (permalink)
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02 Impala 3.8 bucking at around 20mph

Hello everyone

My car starting feeling like a constant miss randomly at anywhere from 40 to 70mph. It almost felt like a spark plug wasnt making contact. That is not the problem (spark plug). It seem like when I would go up a hill you could really feel it missing. Like when you put a load on it. It does not do it idling. Now today it started bucking really bad at around 20mph. The tranny seems to be changing hard at this speed also between 20 and 30 mph. The tranny was replaced last year so I dont think that's the problem. No codes come up when placed on the computer. I dont know if this is 2 separate issues or just one the missing at 40 to 70 and the bucking at 20. My husband was able to keep the car at 20 mph while the car kept bucking as long as he kept the car at that speed. Fuel filter changed no difference. Need help! Why doesnt any codes come up? There is definitely something wrong.

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Old 04-04-2011, 08:03 PM   #2 (permalink)
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when is the last time you had the tires balanced and also a front end alignment? cheapest first is a local tire shop for tire balance...also has you checked the upper motor mount? last if the tranny was recently replaced...was the cv joints looked at or replaced?

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Old 04-04-2011, 11:56 PM   #3 (permalink)
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1st. check fuel pressure. 2nd check for exhaust restrictions. 3rd check for spark at all 6 cylinders. 4th unplug MAF sensor. 3.8 can run on speed density. if it runs normal then its the MAF. doing these simple tests should help diagnos this problem. update when you can

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Old 04-04-2011, 11:57 PM   #4 (permalink)
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Quote:
Originally Posted by iraqichad View Post
when is the last time you had the tires balanced and also a front end alignment? cheapest first is a local tire shop for tire balance...also has you checked the upper motor mount? last if the tranny was recently replaced...was the cv joints looked at or replaced?
the balance would affect it at all speeds...

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Old 04-05-2011, 05:45 AM   #5 (permalink)
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Tires are brand new. Front end aligned. CV joints new. This is nothing to do with the tires. It's an internal miss. To give you another description of the miss at 20mph. Its like when you are trying to start out in a too high a gear in a manual transmission and the car bucks and carries on. That's the bucking I get at 20mph. Thanks for any input

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Old 04-05-2011, 08:13 AM   #6 (permalink)
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Quote:
Originally Posted by synysterjoe View Post
1st. check fuel pressure. 2nd check for exhaust restrictions. 3rd check for spark at all 6 cylinders. 4th unplug MAF sensor. 3.8 can run on speed density. if it runs normal then its the MAF. doing these simple tests should help diagnos this problem. update when you can
This is good advice, and fairly cheap/easy to do.

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Old 04-05-2011, 10:51 AM   #7 (permalink)
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uh..... the only thing i can think of is maybe you have a bad ground of loose wires in the either the ckp or cmp. have a wave form taken of both and see... does it ever just not start every once in a while?

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Old 04-05-2011, 11:01 AM   #8 (permalink)
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no it has always started. It does once and awhile when it turns over it sounds like it dies and then quickly like revs but nothing consistently. The car runs strong no lack of power. Would a code show up if it has to do with the tranny? or the 2 selenoids in the valve body?

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