Engine low power?

Tiny
GEORGE PIERCE
  • MEMBER
  • 2003 CHEVROLET IMPALA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 171,000 MILES
My 03 Impala began losing power under load, I had code scan done by an ASE shop. They said the codes indicated a misfire and overheating. They said that the intake manifold gasket was leaking coolant. I changed the intake manifold gasket and the T-Stat. I check the EGR valve and found that it was apparently stuclk because I checked it by checking the plunger valve with a small screw driver. I felt a small "pop". I took the valve apart and cleaned it with WD40, then wiped the valve dry and used air to dry the excess oil. After installing the new manifold gasket, the engine did not accelerate any better. IT just seemed to fall flat when trying to accelerate above 18-20mph. I was driving it out of town on a 20 mile trip. After about 4 miles the check engine light came on again. A friend had a scan tool, when we checked for codes it came up with a p0300 code. This was after I had changed the plugs, the IACV, it was stuck and I messed it up taking it a part, so I replaced it. I've changed the plug wires and cleaned the plugs I changed the fuel filter and checked the air filter. We checked for a vacuum leak by using carb cleaner around the air plenum, etc. What should I check and in what order? I am retired with high medical cost and therefore I have to try to make the repairs myself. Thanks, George
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Tuesday, August 10th, 2010 AT 3:26 PM

45 Replies

Tiny
DOCFIXIT
  • EXPERT
Hi
Two things to do have fuel pressure checked and clean MAF if 3.4 L in air intake plenum if 3.8L see

diagram


https://www.2carpros.com/forum/automotive_pictures/198357_Graphic_559.jpg



This guide can help as well

https://www.2carpros.com/articles/engine-has-low-power-output

Please run down this guide and report back.

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Tuesday, August 10th, 2010 AT 3:55 PM
Tiny
MERLIN2021
  • EXPERT
When the intake gasket was fixed, did they do this?
Reference Number(s): 03-06-04-056, Date of Issue: September 29, 2003 Related Ref Number(s): 03-06-04-056 ARTICLE BEGINNING SERVICE INFORMATION A new gasket has been released for use in the above vehicles. The new gasket will seal better than the previous gasket. When changing this gasket, be sure to check the bottom of the throttle body for any flashing. Any flashing that protrudes more than 0.50 mm (0.020") should be filed by hand. Use caution that the sealing surface is not damaged. Flashing in the areas indicated between the arrows, ( Fig. 1 ), is the most critical as it can effect the sealing of the upper to lower intakes. Be sure that all surfaces are clean of any foreign material before installing new gasket. Fig. 1: Throttle Body PARTS INFORMATION
BUICK: 2000-2003 LeSabre, Park Avenue, Regal with 3.8L V6 Engine (VIN K - RPO L36) CHEVROLET: 2000-2003 Impala, Monte Carlo with 3.8L V6 Engine (VIN K - RPO L36) PONTIAC: 2000-2003 Bonneville, Grand Prix with 3.8L V6 Engine (VIN K - RPO L36) SECTION: 06 - Engine/Propulsion System


https://www.2carpros.com/forum/automotive_pictures/62217_TB_1.jpg



https://www.2carpros.com/forum/automotive_pictures/62217_gasket_1.jpg

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Tuesday, August 10th, 2010 AT 4:02 PM
Tiny
SKENNEY37
  • MEMBER
  • 2003 CHEVROLET IMPALA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 157,000 MILES
It just started 3 days ago and getting worse. OBD2 reads code P0420. From 20 to 50 mph it seems to have a loss of power when I step on the gas. Do you suggest with code given the catalyst converter needs to be replaced?
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
RENAUDTN
  • MEMBER
Yep; the code and the lack of power at higher speed are typical of a plugged converter resulting in excessive back pressure.
Check exhaust backpressure to makes sure.
In your case it went bad probably because it had 157,000 miles on it, however a bad converter is sometime the result of another problem such as worn exhaust valve, leaky head gasket, cracked cylinder, bad coolant sensor, etc.
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
HARTLEYKID
  • MEMBER
I have a 2003 chevy impala no code are on but it loss power when I step on the gas what can be the problem.I tried this egr valve mass air flow sensor tps coils ignition control module what can it be please need help
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
DRCRANKNWRENCH
  • EXPERT
Check the fuel pressure. There is a test port on the fuel rail. Auto Zone or Advance Auto has fuel pressure test gauges they will loan out if you give them a deposit.
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
RCAREY4128
  • MEMBER
  • 2003 CHEVROLET IMPALA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 122,000 MILES
Problems started a few weeks ago. When accelerating car bogs down and slowly picks up speed.
From a stop it is good up to about 30 then the problem kicks in.
On the hi-way driving along is ok until the road goes up hill a little, speed slows down rpms jump up and down and car bucks.
If accelerating at this point it does nothing and sometimes will drop into neutral and tach out.
Also get random misfires every once in a while.
So far since the car has high miles I have replaced fuel filter, plugs, wires, coil packs, ignition control module and mass airflow sensor.
Also fuel pressure regulator had slow vacuum leak and was replaced.

What else is left to replace to try fixing this?
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
DOCFIXIT
  • EXPERT
Seems the transmission is the issue and is slipping
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
RCAREY4128
  • MEMBER
Transmision people say not transmision problem. Car runs almost perfect with new mass airflow sensor unplugged. Exact same problem with old and new sensor. Only slugish at highway full throttle with unplugged.
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
DOCFIXIT
  • EXPERT
When engine runs better with MAF unpluged then cam sensor is usually at fault. 3.4L or 3.8 L
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
HARTLEYKID
  • MEMBER
  • 2003 CHEVROLET IMPALA
  • 143,456 MILES
I have a 2003 chevy impala no code are on but it loss power when I step on the gas what can be the problem.I tried this egr valve mass air flow sensor tps coils ignition control module what can it be please need help
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
ASEMASTER6371
  • EXPERT
Sounds like a clogged cat converter. A shop can do a snap throttle vacuum test to verify.
Also, have the fuel pressure checked as well.

Roy
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
HARTLEYKID
  • MEMBER
Check the cat converter was not the problem I will check the fuel pressure in the morning
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
MKMATT56
  • MEMBER
  • 2003 CHEVROLET IMPALA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 299,942 MILES
My car gets to 30 mph and then takes another mile to get to 35. The RPMs keep increasing (I can hear it), but the car goes no faster. If I raise my foot from the accelerator, I can 'force' the engine to downshift and I can get to 40-45. Then it stops accelerating altogether. I think 48 is the top I reached tonight on a 20 mile trip. The motor sounds like it's running OK, and I have no drips on my driveway. My dealership told me yesterday it was a plugged converter. I made an appointment to get it replaced on Monday, but tonight on the way home my check engine light came on. (Had not doe this previously). When the problem first started my first thought was transmission because it acts like the motor wants to keep winding and nothing's getting to the drivetrain. Is it still safe to drive? The shop I need to get it to is about 30 miles from home. Please answer soon! Thanks Marci
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
JACK42
  • EXPERT
It does sound like aplugged cat. If you want to see, loosen the exhaust pipe at the manifold, before the cat, if thecat is plugged it willl run, loud but it will run. The check engine light is most likely a "cat efficiency" code, they throw those codes when the cat is having problems
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
RSLICH
  • MEMBER
  • 2003 CHEVROLET IMPALA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 170,000 MILES
Hello. My Impala starting shifting very late, and you had to sort of feather the throttle to get it to shift at all. It did this for about a week, and while this was going on it started to loose power. I don't believe the power loss started until after the shifting problem. I replaced the TPS, and reset the code. The check engine light is now off, but I'm still experiancing a severe power loss. It seems to idle fine, if you rev it in park you can notice a little roughness, not really a hesitation so much, almost like a rev limiter is kicking in early, but that's not exactly it either. I've replaced the plugs and wires, and bench tested the coil packs, which appear to be ok. The exhaust seems to have pretty good pressure, so I'm not thinking it is the cat. I guess I'm now thinking it could be a fuel pump and/or filter, bad injector, maybe a bad fuel pressure regulator? I don't have a fuel pressure tester.
What do you think?
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Monday, January 6th, 2020 AT 3:56 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • EXPERT
I think it would be a good idea to check the fuel pump pressure. Most parts stores will lend or rent them to you. If you can't find one, they sell them on this site under the test equipment store.

Let me know what you find. You may also want to check for intake leaks and actually check back pressure at the converter and before it.
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Monday, January 6th, 2020 AT 3:57 PM (Merged)
Tiny
DMCPHAIL
  • MEMBER
  • 2003 CHEVROLET IMPALA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 103,000 MILES
My 2003 Impala has no acceleration. It idles and starts fine but when I start driving it has less acceleration the more I push the gas. If I run the RPM's too high it begins to made a detonation sound. I have replaced the fuel filter, air filter, and cleaned the mass air flow sensor. It also has good fuel pressure coming from the fuel pump. I did notice that the idle air control valve was dirty but it idles just fine. There are no codes coming up either. Please help!
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Monday, January 6th, 2020 AT 3:57 PM (Merged)
Tiny
BLACKOP555
  • EXPERT
After car is warmed up put car in first gear. Put on brake so car dont move and floor it. What rpm does the engine stabilize at?
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Monday, January 6th, 2020 AT 3:57 PM (Merged)
Tiny
DMCPHAIL
  • MEMBER
  • 2003 CHEVROLET IMPALA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 103,000 MILES
My 2003 Impala has no acceleration. It idles and starts fine but when I start driving it has less acceleration the more I push the gas. If I run the RPM's too high it begins to made a detonation sound. I have replaced the fuel filter, air filter, and cleaned the mass air flow sensor. It also has good fuel pressure coming from the fuel pump. I did notice that the idle air control valve was dirty but it idles just fine. There are no codes coming up either. Please help!
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Monday, January 6th, 2020 AT 3:57 PM (Merged)

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