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Discussion Starter #1
I have a 2002 Impala with 120k miles on it. Being only 17 and not an expert on modern cars, I have noticed my car was running slow. It wasn't until my father drove it I noticed it was a real problem. (I was used to an old 352 V8)

After my engine becomes warm, the acceleration becomes slower and slower. The car usually changes into 2nd gear at 35MPH, and that is when the real slowness appears. Once it transitions into 2nd, the car drastically reduces its acceleration power, leaving me behind of passing cars. I actually have to step on the pedal a bit more so it can "kick in", though it often takes a few seconds to notice I actually want to use some power (probably the computer). It's almost like 2nd gear has two modes, with the first mode being incredibly low on power.

This slowness of acceleration also happens in higher gears. For example, when driving 50MPH on the highway and wanting to accelerate around a slower car, I have to actually drop it down 2 gears to actually have some power. It is quite annoying, and I wish to stop "abusing" my car trying to suffice with the power it lacks.

I've been searching around on the internet and found some things that could help. Replacing spark plugs & cables, a new coil, cleaning the fuel filter and injectors, a new fuel pump, or a new exhaust.

I just really want some insight on to what my best option would be and why my car is doing this. Any help or idea is appreciated.
 

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The Unscrupulous Lt. Colonel
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Well all the stuff you mentioned that may need to be replaced is a excellent start. But the thing is the ls Impala is only 200 horsepower and the base version at 180. Because as stated you are use to driving a above average v8, until you get a driving 'sense' or 'feel' of a slower v6, it will seem like you are driving a real slopoke, although you are not...

Id like to suggest to taking it to a mechanic or maybe have pop drive it to make sure its nothing wrong with your vehicle. From a vague discription, i would say something maybe wrong with your fuel system via fuel pump. But im thinking its more of getting the feel of a semi slower vehicle. Its like driving a 100 mph for an extended period of time, but then driving regular/ crusing limits lets say 50-55 mph. It will seem like you are driving like a old ass.
 

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Discussion Starter #3
Thanks for the reply. I'll try and get my car in to a professional to find out what the problem is.
 

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8th Gen Antagonist
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I have to agree with Kane, one thing to note as well is that these v6's have a narrower powerband than a big v8, therefor will seem like it's losing power when it upshifts.
 

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Discussion Starter #5
Alright I'm back. I have replaced my fuel filter and spark plugs. I have also checked the temps in front and behind of my cat. Turns out my exhaust is fine and has no build up in pressure (based off of lower temps in front of the cat).

If it is not any of the simple problems I thought it was, then it might be something computer related. If so, would a performance chip correct timings, fuel mixture ect? I will probably end up taking it to a shop on Monday or Tuesday.

I also have started noticing that if I work the engine hard when it is cold and has a little more power, when it becomes warm the power loss seems more significant.
 

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8th Gen Antagonist
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There is no "chip" to speak of, you can get a PCM retune, but isn't going to help this situation. I take it there is no check engine light? I hope you would have mentioned it by now if there was. Does the temperature gauge seem high when this is happening? Does it sound any different when its acting like this? I would try testing the intake air temp sensor, the fuel pressure, and the ignition control module. I may be wrong, but I'm guessing its one of those things.
 

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Discussion Starter #7
Oh sorry, the check engine light isn't on. And when this happens, the temps seem normal but the engine feels like it is shaking slightly. The engine also sounds like it is being flooded, at least that's how I can explain it. I'll google around to see how to test those things.

One more thing to mention is that when I see videos on YouTube of people going 0-60, their times usually are around 10 sec (same base model as mine) and their tires spin when taking off. When I floor it from idle, it just feels flooded and tires aren't even close to spinning. Other impalas I see also seem to go all the way up to 50MPH before going into second, where mine tops out at 35MPH and hesitates to go into 2nd for about 3 sec. My 0-60 time is 30 seconds.
 

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Discussion Starter #8
I've recorded a video:

Notice the slow start and how it won't change to 2nd after a while (and how my car stops accelerating in first gear when it reaches 38 instead of 50 like others). Then once in 2nd, no power at all and car shakes a little bit.

Compare to
and
 

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8th Gen Antagonist
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Wow, that is pretty bad. I guess just follow up on those tests I mentioned for now, see where it gets you. For the fuel pressure you need a tester, they are $40-45 at the auto parts store, you may be able to rent or borrow one. The other two items you just need a digital multimeter, I don't remember the procedures off hand, but if you can't find the info by tomorrow let me know and I'll be able to look it up for you.
 

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Discussion Starter #10
I'm going to go test my MAP sensor right now. As for the fuel pressure, I may have to take it in to get it looked at because it looks complicated and is worth the $40 to have somebody check it instead of buying the tools and testing yourself.

I'll be back to say how the MAP sensor test went.
 

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Discussion Starter #11
MAP sensor works. And I think I'll wait on that fuel pressure test until I get a diagnostic check.
 

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8th Gen Antagonist
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You can get the tester for the same money, and then you have the tool for future use. It's not complicated to use, and its near impossible to get the results wrong.
 

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You can get the tester for the same money, and then you have the tool for future use. It's not complicated to use, and its near impossible to get the results wrong.
wow i second this idea tremendously, i had a fuel pump going out and did not know it untill i bought a pressure gauge and checked it myself,
if you can screw on a valve cap on your tires and also read then this is the tool for you! ......
 
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Ok just wanted to throw this out there. I have the same year car as you with 228k miles and i tend to have similar issues i believe my problem is my transmission pressure solenoid. Replacing that is quite a process and i have not looked into doing it to much due to my high miles. I hope this helps you or provides everyone with other ideas that may help you.
 

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Mr. Handy
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I believe in most cases bogging down is due to a clogged cat converter or faulty fuel pressure regulator or bad fuel pump.
 

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Since he said the temps before and after the cat are about the same, wouldn't that rule out a clogged cat? I would think that a clogged cat would cause the temps to be much higher before the cat (they were actually lower, according the OP).

Sent from AutoGuide.com Free App
 

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Mr. Handy
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Yes he ruled that out but not these new posters.
 
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