03 Impala power loss

Hey, not a newbie but have rarely post here. My mom has an 03 Impala that starts fine and idles smooth. When you put it in gear it has just doesn't have much power to get going until it picks up enough speed to go into high gear. Then it runs fine until you give it gas and it downshifts and then no power again. I don't think that it feels like the trans is slipping. If you rev it up while in this power loss mode it sounds like the valves are floating or knocking. If you rev it up while in park, it sounds like valves floating or knocking. Is there any kind of switch or sensor on the trans for the lower gears? Any help or suggestions would be great.

Milage? Any codes? When was the last tune-up? Can you get an accurate reading of the fuel pressure? Don't know if a clogged cat would do this, but may be worth looking in to. Try cleaning the throttle body.

The milage is 91,000. She said that the check engine light has not come on but she's going to get the codes checked just in case. The last tune-up was last summer (don't know the milage at tune-up). Don't know about the fuel pressure. She's tried Seafoam in the gas with know change. What process to clean throttle body?
Thanks

The milage is 91,000. She said that the check engine light has not come on but she's going to get the codes checked just in case. The last tune-up was last summer (don't know the milage at tune-up). Don't know about the fuel pressure. She's tried Seafoam in the gas with know change. What process to clean throttle body?
Thanks

the cat converters of these vehicles have plugged up causing your mothers power problem ....recall for defective converter failures..

seafoam isn't gonna help....get the exhaust checked for restrictions...

Sounds like the CAT. I have a 03 impala to. Mine did the same thing. it will not throw off any codes or make the check engine light come on. yeah it sux..it costed me like 800 bucks at the dealership. it took them 2 days for them to change it... but good luck.. lets us know what happens

Ok. I told my mom about the probability of cat. conv. In the mean time the check engine light came on. Had it checked and came up ox. sens. was bad. I told her that was probably true cause with the conv. backing up fumes and excessive heat, it either choked it out or cooked it. She took it to a garage and they used a "heat sensor" to check the conv. and said the conv. was fine and said that it needed a ox. sens. I can't emagine the ox. sens. causing this problem. Is there a proper way to check the conv? Going by the symptoms and the responses that I have gotten on this forum, I'm still leaning torwards the conv.
Thanks

If it was a code for a Front O2 Sensor, it COULD just be the sensor, the engine needs that one to define fuel trims etc. If it was a code for the REAR O2 Sensor, it's probably a bad Cat. They need to do a flow test on the exhuast.

It was the code for the front 02 sensor. And they did check the exhaust flow. I will try to put the sensor in this weekend and hope that it is the problem.Thanks again and I will post the results.

Well I put the 02 sensor in and no change. In another thread on this forum, "crazy Jim" suggested to someone to remove the 02 sensor and try it. I did and the car seems to take off better. It's a little noisy and I realize that it's trying to exhaust out of a small hole, but it would spin the front tires in the gravel. So it may be the cat conv as you'all suggested. Do I need to replace the whole exhaust or just the conv.?

Well I put the 02 sensor in and no change. In another thread on this forum, "crazy Jim" suggested to someone to remove the 02 sensor and try it. I did and the car seems to take off better. It's a little noisy and I realize that it's trying to exhaust out of a small hole, but it would spin the front tires in the gravel. So it may be the cat conv as you'all suggested. Do I need to replace the whole exhaust or just the conv.?

the repair tech's you went to are idiots...the exhaust is checked for restictions,,,usually a pressure gauge upstream, then downstream of the cat converter...or as I sometimes do, just remove the upstream sensor and if it has more power then you know its plugged up..

as I stated before this is a common failure and may be still covered under warrantee as it was free for most to correct....at Goverment Motors....

After my other post, I decided to try it on the hwy with 02 sensor still out and the car got up to 60 mph pretty quick. Didn't try to push it, not sure of what it was going to do. Let it cool down and put 02 sensor back in and hit the hwy. OMG I had to turn the e-flashers on so that I wouldn't get freight trained from behind. The car barely got up to 30 mph. Scarey!

DEF. Sounds like the cat. its plugged, so exhuast barely has anywhere to go. by removing the front O2 sensor, you've given it a place to escape.

On the bright side, a new front 02 sensor was not completely in vain, when its all fixed up, could help your fuel millage by 1 - 2mpg if your old one was fouled up age by time and millage.

I figured the 02 sensor was probably cooked from the extra heat.
The cat conv shouldn't be too hard to change if you have the car up on a lift should it? It looks like there's a flange with 2 bolts at each end along with gaskets. Is there any special tools or tips that I need to know about? My neighbor has a lift at his garage and said that I could use it.

I figured the 02 sensor was probably cooked from the extra heat.
The cat conv shouldn't be too hard to change if you have the car up on a lift should it? It looks like there's a flange with 2 bolts at each end along with gaskets. Is there any special tools or tips that I need to know about? My neighbor has a lift at his garage and said that I could use it.

I would have a muffler shop install your cat converter...get the correct converter and then have them install...

you need high powered torches and the knowledge to use them...in most cases....this will prevent bolts/manifold damage...they will replace that in less than 30 min...including lift time..

don't put new O2 sensors in until the cat breaks in a couple of miles..that way they won't get possibly contaminated by any oils/antisieze compounds...etc...

The part as a whole with the Flanges Is actually the Downpipe. If you take it to a shop, they will most likely cut out the cat it self and weld in a new aftermarket one. a GM Dealership will probably replace the whole downpipe though.

Rockauto.com has direct fit cats (flanges at both ends) for $200 or less. I got a cat set (2 cats with pipes) from them for my Tahoe and was very pleased. These cats are not for sale in California, but being in Virginia, who cares?

Thanks, when it comes to exhaust pipes, there's always things that just don't
go as planned. I really didn't want to do it but was willing to try to save some money. You guys gave some good points.

I had the same problem on my 03' impala. It cost me around $400 to replace the cat at a muffler shop last year! It is always one thing after another on my impala!!! :runaround:

yeah it sounds like the cat.. i had the same prob wit my 03 impala. i payed 800 bucks for mine at the dealer.. if u is not a mechanic i suggest u take it to the shop..

It cost $250 at a muffler shop. They cut the old one out and welded a new one in. Works for me.

It cost $250 at a muffler shop. They cut the old one out and welded a new one in. Works for me.

toughnut,

how is the new cat working for you? My engine check light came on after I had mine replaced. It works fine, it just throwing a code for the rear o2 sensor.

The car is running great. It's my mom's car but I keep asking how it's doing (being I'm the one that suggested the repair process). You know, kinda leery of suggesting to someone else how to spend their money for repairs. She's impressed with the power that it has. I think the power loss was gradual and didn't realize what was going on with the car. No codes so far.

toughnut,

how is the new cat working for you? My engine check light came on after I had mine replaced. It works fine, it just throwing a code for the rear o2 sensor.

I've noticed somethings changed, that long as the temps above 40F My Cat CEL doesn't come back on. So pay attention, might notice yours just disappear one day and stay out :D

I appreciate the info.