Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
2008 impala 3.9
Car has this hesitation under a load. Like going up an incline. Press the gas you can feel it does not want to go.
Super bad MPG. About 250 260 miles per tank. Was 200 MPG per half tank.
Car has NO CODES. NONE. Money light is OFF……
1 Garage looked at it for 20 min and said I needed a new catalytic converter. Said it was clogged.
They put on a Walker aftermarket cat. And a new O2.
I didn’t notice anything right away. But After 1 day It was doing the hesitation thing. Then the money light comes on. I have this THINK DIAG reader and also took it to auto zone and I get the P0420 code. Amazing huh?
I took it back the garage and had it 2 hours and IDK what they did but in the end they just sprayed out the MAF.
Now I go to the Chevy Steeler and they see the p420 and know It has an aftermarket cat and they want to charge 300 to take it off to inspect it. I left.
Back to the garage, this time they did this induction cleaning and replaced the upstream 02. . They said the 02 has signs of coolant on it. Maybe so, but I have not put coolant in my car forever. (Never suggested this on my 2nd visit) a day later p0420 is back and the problem is still there..
Now they want to remove the cat and replace it with a test pipe as a test of some sorts…. IDK what that will do. What do you all think?
I know, Paul, has said GM needs to be OEM cats. But now I wonder if the original cat was ok. They swear it was clogged and heavy. But they didn’t know it was heavy until they cut it off. I asked what test was used to determine it was clogged. He said they used a temperature. And some reading of some sort.
Just seems odd i had problems but no code. They replace my cat now I have a code. I just cant see spending 1000 more just to have my same problem.
Idles fine. Red light to 40, many times it’s a smooth as can be.
Plugs and wires changed less than a year ago..
This would make a great case study car.
Idk what else to add. Im venting more than anything. I know no one can help much without seeing it .
Last edit: 3 years 5 months ago by imapartschanger.
Topic Author
