Hello all, new to the forum. Last week my 2003 Monte Carlo SS started having problems accelerating, especially going up hill. When driving normally and on the highway, the car takes forever to accelerate up to speed (25-60mph). When driving up hill, even if i was going 50 before hitting the hill, my car will drop down to 20-30mph, and stepping on the gas does nothing to help.

Now I first thought it could possibly be the catalytic converter. So I used an IR gun to test the temperature near the front of the cat and near the back, but the temperatures seemed normal. The temp didn't get extremely high and the cat didn't look that hot either. I also don't have any codes coming up for it. So i am guessing that's not the issue but not sure.

My second guess is that it could be my fuel pump and/or filter. I haven't been able to test it yet but will try soon.

Anyone have an idea what it could be?

 

I would suspect the fuel filter since the problem seems to occur during high fuel demand. Sounds like flow is restricted. Can be tested with a fuel pressure gauge you can rent from a parts store.
Inexpensive and easy to replace unless there's rust around the fittings. I would try that first.

 

Update: Today I went and replaced the fuel filter, cheap, but didn't notice any difference really. So I went ahead and replaced the fuel pump, this time a noticed a difference. Car seemed to not struggle as much when accelerating but when it did struggle going up hill, it was when it was trying to break the 3000rpm that it would sputter and stay at 20-30mph....
Still satisfied with replacing the fuel pump/filter, seemed to have made a difference. But it seems it has to be the catalytic converter now, not really sure what else it can be. I see some Magnaflow's going for $180-250, and seems like it shouldn't be that hard to replace. Hardest part i think would be removing the old one. I will update again when I try it, but feel free to share any thoughts.

 

If the cat is clogged it should throw a code P0420 (Catalyst System Low Efficiency). If you do have to replace the cat, make sure you don't have a California emissions system car which requires a different (more expensive) cat. There's USUALLY a sticker on the driver side above the radiator that say's if it does. Buy a "Direct Fit" cat and it's just a "bolt-in job". The hardest part to replacing the cat is getting a socket on the nuts where the downpipe connects to the manifold which takes a 2 ft. extension on the ratchet. Buy 4 new stud bolts and replace them in case they break or are badly rusted. Soak the nuts with PB blaster or Aerokroil penetrating oil the night before you do the work.

 

Would check the throttle body for oil deposits that cause throttle body to stick. It might help with the acceleration problem. On both the grand prix and the monte the throttle body was coked with oil. Had to disassemble both and heavy clean. As long as none of your parts arent bad only part you will need will be a throttle body gasket. Easy job, except for the support bracket that attaches to the lim and the throttle body. That's a B****

 

my 07 Impala SS is seriously sluggish and has a burning rubber smell coming from the exhaust, I`m betting on the catalytic converter. theres a magnaflow universal listed on amazon.ca for 108$ cdn.

 

I agree, that would definitely be worth checking as it would limit air flow resulting in a rich mixture. If you have access to a OBD 2 scanner capable of reading real time fuel trim values the problem could be seen as short term and long term values higher than +0%. 0%ST and 0%LT is ideal. -(minus) values mean a lean condition, +(plus)values mean a rich condition.
A vacuum leak can also cause this which can be detected by interpreting fuel trim values.

 

Update: Thanks Plumbob for the advice. I tried to do it myself but was unfortunately not successfully, one of the nuts that attach to the bolt on the resonator end of the catalytic converter was extremely rusted out. I sprayed it 2 nights in a row before I did the work, even used a torch to heat it up, but it was so rusted that it was the shape of a thimble so I cant grip it well or get it loose.

I ended up finding a muffler shop near me that did everything thing for $445, and my catalytic converter was clogged as I suspected. They installed a new Walker (CARB) catalytic converter. I picked it up today after work and my car drives like new, feels much better than it did even before I started having the issues.

Wanna thank everyone again for the help, I would have been able to do it myself if it weren't for the one nut/bolt.

 

Glad to hear you're back up and running ares. Those bolts/nuts can be a real pain. Think I paid $190 after shipping for a DAVCO CARB cat from RockAuto, so it sounds like you got a fair deal. Thanks for the update.

 

Good to hear problem fixed.

Follow up question:

What plugged it and thus will it plug again if you don't know why it plugged.