2003 Impala Base hesitates, bogs up to 20 mph

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A friend of mine at work is having trouble accelerating with his Impala until it gets up to about 20 mph, then it is fine. He has had it to 2 transmission shops and both shops say it's not the transmission. One shop put it on a diagnostic machine. His mechanic still thinks it's the transmission and changed out the oil, didn't fix it. My friend is very short on funds. There is no engine light. Car has 135K and hasn't been tuned up since new. I suggested starting with plug wires. With very limited funds how would you proceed? I guess first testing the wires would be my suggestion.
 
No engine light as in the CEL isn't on or it isn't working? I wonder if it's maybe starting out in 2nd gear. First thing Id check is the plugs and the air filter
 
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It could be something to do with the ignition but I had an 07 Malibu (3.5 liter) that did the exact same thing and nobody could figure it out. Indy shops, dealerships (said it was because the engine ran lean, morons) etc. I ended up trading it in for my Equinox. I had/have no idea why it did it. Best of luck for your friend. I hope somebody else could help him.
 
What engine is in the Impala? If it's the 3.8L it may be a sticky EGR valve. Both my Dad and Brother had this issue but it would result in low power throughout the rpm range until it unstuck. If it's the 3.4L I don't have any history with that motor.

I would think a ignition issue would get worse with higher RPMs. However, weak plugs, wires, and coils could make another issue worse.
 
I'm voting on it having a clogged/broken catalytic converter

Here's a picture I took last month of my brother's Chevy truck's catalytic converter we took off due to it having so little power it wouldn't even drive.

2w2llar.jpg
 
How many miles on this engine? Any recent work? Better diagnostic work is indicated. Long/short fuel trims, a good session with a vacuum gauge (the most underrated and one of the best diagnostic tools you can own) and fuel pressure gauge will reveal a lot about whats going on in the engine including a clogged cat.
When was this engine last tuned up, filters changed, throttle body cleaned, etc?
 
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How many miles on this engine? Any recent work?


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His mechanic still thinks it's the transmission and changed out the oil, didn't fix it. My friend is very short on funds. There is no engine light. Car has 135K and hasn't been tuned up since new.


I'll look into the uses of the vacuum gauge. Do you suggest a particular one for home use?
 
A vacuum gauge is a very simple gauge and doesn't cost a lot, its an amazing diagnostic tool if you learn to read it and know what the readings mean. Mastering this little tool will help you be a much better mechanic.
Look at this one, it works fine and has a case, I own it. No reason for anything more expensive for the basic functions.

https://www.amazon.com/OTC-5613-Vacuum-Pressure-Gauge/dp/B0050SG9KW

Some interesting articles.

http://www.gregsengine.com/using-a-vacuum-gauge.html

https://www.motor.com/magazine-summary/mastering-the-basics-reading-a-vacuum-gauge/

http://www.autospeed.com/cms/article.htm...tics&A=2393
 
BTW, I had the exact same symptoms with out 2001 Impala about a year ago and it was a bad ignition coil. It is smart to replace all 3 of them. I only replaced one and then a couple of months after that another one went bad.

The symptoms were a lack of power and a hesitation when pulling out. Almost like it was trying to pull out in second gear. Once it got rolling the engine smoothed out some. When you really required torque from the engine like pulling out going up a hill it was the worst. And the car only had 86K miles on it at the time.
 
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Coils, spark plugs, wires (if any)

NGK Laser Iridium plugs, NGK wires, OE or Denso coils

If you have remove the intake to get to the back cylinders, then replace the valve cover gaskets too
 
When our 2001 Impala had the bad ignition coil(s) it did not have a CEL light up, it just seamed like it was trying to pull out in second gear because it would stumble in power.
 
Originally Posted By: JimPghPA
When our 2001 Impala had the bad ignition coil(s) it did not have a CEL light up, it just seamed like it was trying to pull out in second gear because it would stumble in power.


That would make sense, if the coil isn't firing a cylinder it might not detect a misfire.
 
Originally Posted By: schuylkill
Car has 135K and hasn't been tuned up since new.


Start with plugs, wires, PCV and filters before doing anything else at 135K the gaps may have eroded badly on this waste spark engine.
Don't start throwing coils and modules at it, always start with what you know needs replacing and go from there.
This engine requires double precious metal tip plugs as it has waste spark ignition regardless if its the 3.4 or 3.8 AC Delco double platinum work well in these.
Its easier to do if you disconnect the dog bones and roll the engine forward.
 
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Its easier to do if you disconnect the dog bones and roll the engine forward.


Dog bones? I'm new to the repair of GM and Ford vehicles. (aside: I just bought a 1996 B4000 truck.)
 
Originally Posted By: schuylkill
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Its easier to do if you disconnect the dog bones and roll the engine forward.


Dog bones? I'm new to the repair of GM and Ford vehicles. (aside: I just bought a 1996 B4000 truck.)


Engine mount - also called the torque strut. You'll see them as soon as you open the hood and why they're called dog bones.
 
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