2002 Malibu Code P0300 and P0420

I just purchased a 2002 Malibu at auction to help out a friend, but have run into some unexpected problems as I am not familure with these cars. When I picked up the car a drove it about a 100 yards to the car trailer. It seemed a little sluggish to me for a V6 and really seemed to not have much power. It seemed fine at Idle. It did have a an engine light on. Once a got the car home, I checked the codes.. P0300 (Random/Multiple Misfire) and P0420 (Catalyst efficiency below threshhold ) I cleared the codes and I have only gotten the P0300 code back in the little testing below that I have done thus far. I am hoping givin the below information below that someone might be able to point me a good direction before I have start dumping huge or needles funds into this car. Car is in over all great condtion though it does have 109K.

The basic symptoms of the car are:

At idle it seems to me the car sounds fine. When you rev the motor it usually is not able to hit the Rev Limiter.. wich I understand is at appox 4000 RPM. Basically you can mat the gas pedal to the floor and the car will not hit more the 3500 RPM and subsiquent tries in succession usualy result in hitting lower and lower RPMs. Doing the multiple succession of reving has resulted in a pending code of P0300 twice. When driving the vehicle, it seems to start out fine, but as you try to acclerate the motor seems to bog down starting around 5-10 MPH and continues to do so up to the attainable speeds of around 40MPH I was not able to go faster then that partialy because I dont think the car will and that I am only able to work with the car in a parking lot. I am not able to get it to throw a code agian while driving so far, but have done limited driving with it... only the testing I have done.

Along with the above testing and driving I had purchased 1 coil set.. I have systematicly swapped the new coil into each postion and have wound up with no change in the symptoms above with a test drive around the lot at each position change. I checke the plug wires were tight and connected. I have not yet changed plugs and wires, but will be pulling the plugs to take a look at them. I basically dont want to be replacing everthing under the sun to find out it was something unrealted. so I am on here looking for suggestions and things to look for.

Any help would be great.

from your description it honestly sounds like a plugged cat which would make sense if it has been sitting for a while. You may also want to try spraying some sea foam in the intake until it dies. Let it sit for about 30 minutes and then run it. It will smoke like heck but probably clean a bunch of crud out. Good luck.

not sure i would just spray a liquid into an intake until an engine dies. too much can hydro-lock the motor, or even blow it up. this is of course the worst case scenario. I agree that it sounds like the catalytic converter is clogged, with 109K miles on it, best thing to do is just replace it. sea foam is a great product, i have never seen it clean out a clogged cat. 99% of the time, once one is clogged, is best to replace, if cleaned, will just clog again.

advise to start there, then drive again for a bit to see if the misfire code comes back. clogged cats can and do cause that problem...especially random misfire codes.

I'm pretty sure I wasn't suggesting the sea foam for the cat issue but more for removing some carbon build up on the car with 109k but take it how you want.

Update as of Today:

We worked on the car some yesterday. We changed the plugs and Wires. The plugs looked fine, but being this car is for a friend I went ahead and put in new plugs. After thet we moved on to checking Fuel pressure with a NAPA/ Echlin fuel injection cleaning kit. The Fuel pressure was in the proper range, and while the thing was attached we also did a injector cleaning as well. These items made the car run a little better, but not by a large margin. We still had the major bogging of the motor on accelration and the vehicle in park could still not hit the rev limiter though closer then it had in the past.

We moved on to checking the bad Cat theory. The easiest way to check the CAT we figured to be was to pull the EGR tube out then run the car. Doing this had an instant affect on performance, the car was able to hit the Rev limiter in Park, and had little to no sign of bogging down on acceration around the parking lot. Given the change in performance, we are assuming that the cat is bad. Would people here agree? or is our method of Diagnostic flawed? Could some other thing cause this?

We have assumed that it is the CAT and have a direct swap Wagner Cat and gaskets on Order from Rock Auto for $159. They were not the cheapest, but it was Brand I was familure with where as the Cheapest one had a brand I had never heard of. The local dealer wanted $442.86 for the exact same CAT we have on order and that was with out the Gaskets.

I just purchased a 2002 Malibu at auction to help out a friend, but have run into some unexpected problems as I am not familure with these cars. When I picked up the car a drove it about a 100 yards to the car trailer. It seemed a little sluggish to me for a V6 and really seemed to not have much power. It seemed fine at Idle. It did have a an engine light on. Once a got the car home, I checked the codes.. P0300 (Random/Multiple Misfire) and P0420 (Catalyst efficiency below threshhold ) I cleared the codes and I have only gotten the P0300 code back in the little testing below that I have done thus far. I am hoping givin the below information below that someone might be able to point me a good direction before I have start dumping huge or needles funds into this car. Car is in over all great condtion though it does have 109K.

The basic symptoms of the car are:

At idle it seems to me the car sounds fine. When you rev the motor it usually is not able to hit the Rev Limiter.. wich I understand is at appox 4000 RPM. Basically you can mat the gas pedal to the floor and the car will not hit more the 3500 RPM and subsiquent tries in succession usualy result in hitting lower and lower RPMs. Doing the multiple succession of reving has resulted in a pending code of P0300 twice. When driving the vehicle, it seems to start out fine, but as you try to acclerate the motor seems to bog down starting around 5-10 MPH and continues to do so up to the attainable speeds of around 40MPH I was not able to go faster then that partialy because I dont think the car will and that I am only able to work with the car in a parking lot. I am not able to get it to throw a code agian while driving so far, but have done limited driving with it... only the testing I have done.

Along with the above testing and driving I had purchased 1 coil set.. I have systematicly swapped the new coil into each postion and have wound up with no change in the symptoms above with a test drive around the lot at each position change. I checke the plug wires were tight and connected. I have not yet changed plugs and wires, but will be pulling the plugs to take a look at them. I basically dont want to be replacing everthing under the sun to find out it was something unrealted. so I am on here looking for suggestions and things to look for.

Any help would be great.


It does sound like a cat problem.
But after replacing the cat make sure you do not still have a missfire.
A engine miss will run a new cat if not taken care of.
MT

Here is a little info on a cat code.
DTC P0420, P0421, P0430 & P0431: Check Possible Cause Of Misfire DTC P0420 and P0421 indicates bank one catalyst system efficiency is minimum requirement. DTC P0430 and P0430 indicates bank 2 catalyst system efficiency is minimum requirement. Possible causes are as follows: Use of leaded fuel. Oil contamination. Cylinder misfire. Fuel pressure too high. HO2S sensor improperly connected. Damaged exhaust system component. Faulty ECT sensor. Faulty HO2S. Ensure ignition timing is correct. Retrieve all Continuous Memory DTCs. If misfire code(s) is not present, go to next step. If misfire code(s) is present, isolate cylinder and repair as necessary. Check HO2S Monitor DTCs If DTCs P0136, P0138, P0140, P0141, P0156, P0158, P0160, or P0161 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. Check ECT Sensor DTCs If DTCs P0117, P0118, P0125 or P1117 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. If any codes except P0420, P0421, P0430 and/or P0430 were present in step 1), service as necessary before continuing. If no codes except P0420 and/or P0430 were present in step 1), go to next step. Check Rear HO2S Wiring Harness Turn ignition off. Ensure HO2S wiring harness is correctly routed and connectors are tight. Repair or replace as necessary. If wiring harness and connectors are okay, go to next step. Check Fuel Pressure Turn ignition off. Release fuel pressure. Install fuel pressure gauge. Start engine and allow to idle. Note fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to CIRCUIT TEST HC . Check For Exhaust System Leaks If exhaust system leaks, it may cause catalyst monitor efficiency test to fail. Inspect exhaust system for cracks, loose connections or punctures. Repair or replace as necessary. If exhaust system is okay, go to next step. Check For Exhaust System Restrictions Inspect exhaust system for collapsed areas, dents or excessive bending. Repair or replace as necessary. If exhaust system is okay, go to next step. Ć Check Manifold Vacuum Install tachometer. Connect vacuum gauge to intake manifold vacuum source. Start engine and raise engine speed to 2000 RPM. Manifold vacuum should rise to more than 16 in. Hg. If manifold vacuum is okay, go to next step. If manifold vacuum is low, go to step 11). Leave tachometer and vacuum gauge connected. Start engine and raise engine speed to 2000 RPM. On a non- restricted system, manifold vacuum should quickly rise to normal range as increased RPM is maintained. On a restricted system, manifold vacuum will slowly rise to normal range as increased RPM is maintained. If manifold vacuum is okay, no indication of exhaust leak or restriction has been detected and testing is complete. If manifold vacuum is low or slow to respond, go to next step. Leave tachometer and vacuum gauge connected. Remove exhaust pipe from exhaust manifold. Start engineand raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is downstream from exhaust manifold. Reconnect exhaust pipe to exhaust manifold and go to next step. If manifold vacuum is still low or slow to respond, fault is in exhaust manifold or intake manifold gasket. Repair or replace as necessary and repeat QUICK TEST. Leave tachometer and vacuum gauge connected. Disconnect muffler/tailpipe assembly from rear of catalytic converter. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is in muffler/tailpipe assembly. Repair or replace as necessary and test drive vehicle to verify elimination of symptom. If manifold vacuum is still not okay, fault is in catalytic converter. Repair or replace as necessary. Check tailpipe/muffler assembly for debris from catalytic converter. Test drive vehicle to verify elimination of symptom.

couldn't agree with MT more. as i said would be imperative to re-check for the misfire.

I just purchased a 2002 Malibu at auction to help out a friend, but have run into some unexpected problems as I am not familure with these cars. When I picked up the car a drove it about a 100 yards to the car trailer. It seemed a little sluggish to me for a V6 and really seemed to not have much power. It seemed fine at Idle. It did have a an engine light on. Once a got the car home, I checked the codes.. P0300 (Random/Multiple Misfire) and P0420 (Catalyst efficiency below threshhold ) I cleared the codes and I have only gotten the P0300 code back in the little testing below that I have done thus far. I am hoping givin the below information below that someone might be able to point me a good direction before I have start dumping huge or needles funds into this car. Car is in over all great condtion though it does have 109K.

The basic symptoms of the car are:

At idle it seems to me the car sounds fine. When you rev the motor it usually is not able to hit the Rev Limiter.. wich I understand is at appox 4000 RPM. Basically you can mat the gas pedal to the floor and the car will not hit more the 3500 RPM and subsiquent tries in succession usualy result in hitting lower and lower RPMs. Doing the multiple succession of reving has resulted in a pending code of P0300 twice. When driving the vehicle, it seems to start out fine, but as you try to acclerate the motor seems to bog down starting around 5-10 MPH and continues to do so up to the attainable speeds of around 40MPH I was not able to go faster then that partialy because I dont think the car will and that I am only able to work with the car in a parking lot. I am not able to get it to throw a code agian while driving so far, but have done limited driving with it... only the testing I have done.

Along with the above testing and driving I had purchased 1 coil set.. I have systematicly swapped the new coil into each postion and have wound up with no change in the symptoms above with a test drive around the lot at each position change. I checke the plug wires were tight and connected. I have not yet changed plugs and wires, but will be pulling the plugs to take a look at them. I basically dont want to be replacing everthing under the sun to find out it was something unrealted. so I am on here looking for suggestions and things to look for.

Any help would be great.


You may want to check with the dealer on that one.
They have extended the 8 year 80K warranty on some.
But not sure if it passes on to second owner or auction car or Malibu.

Dear General Motors Customer:

As the owner of a 2001-02 Chevrolet Impala, Monte Carlo; Pontiac Grand Prix; or Buick Regal model vehicle, equipped with a 3.4L or 3.8L V6 engine, your satisfaction with our product is very important to us.

This letter is intended to make you aware that some 2001-02 Chevrolet Impala, Monte Carlo; Pontiac Grand Prix; and Buick Regal model vehicles, equipped with a 3.4L or 3.8L V6 engine, may have a condition where the catalytic converter is replaced due to complaints of lack of power or illumination of the Malfunction Indicator Lamp (MIL). This may be due to the front endcone insulation from the catalytic converter breaking away and blocking the front of the first catalyst brick and preventing the free flow of exhaust gas through the converter.

This is not a recall. Do not take your vehicle to your GM dealer as a result of this letter unless you believe that your vehicle has the condition as described above.

What We Have Done
General Motors is providing owners with additional protection for the Catalytic Converter. If this condition occurs on your 2001-02 Chevrolet Impala, Monte Carlo; Pontiac Grand Prix; or Buick Regal model vehicle, equipped with a 3.4L or 3.8L V6 engine, within 10 years of the date your vehicle was originally placed in service or 120,000 miles (190,000 km), whichever occurs first, the condition will be repaired for you at no charge .

What You Should Do
Repairs and adjustments qualifying under this special coverage must be performed by a General Motors dealer. You may want to call the service department at your dealer to find out how long they will need to have your vehicle so that you may schedule the appointment at a time that is convenient for you. This will also allow your dealer to order parts if they are not already in stock. Keep this letter with your other important glove box literature for future reference.
__________________

New Cat and gaskets are on the way. A call into the dealer said that the extended coverage did not extend to the Malibu. Basically it was a Impala and the like vehicles, though it looks and sounds like the same problems.

I will be sure to make sure the misfire is gone once the new cat is in.