Pontiac Grand Am EGR, Misfire and P0420

• Comments ⇓

2002 Pontiac Grand Am SES light P0404; P0300. Replaced fuel filter, fuel pressure regulator,plugs, plug wires, air filter, and EGR valve. The EGR valve was replaced after the service engine soon light came on.

All other repairs were made before the light came on but after symptoms started to appear. The thing surges,sputters, and just flat runs bad. Has no power to pull itself up hills. If I drive it like there's an egg under the gas pedal, I can run 80 mph on flat ground easily. Start up a grade of any sort and it falls on it's face. Starting out from a dead stop is an adventure too.

That's where it does most of it's spitting and sputtering. It has good exhaust flow and no rattling coming from the catalytic converter. What am I missing here? Why does my car do this. Could a bad gas cap cause this?Could it be a bad PCM?

Answer:
These conditions sure do sound like a plugged catalytic converter. Placing your hand over the tailpipe when revving engine when it has no power can be misleading unless you have done it many times before, or can compare to a car with the same engine.

A back pressure test is the proper way to test that. A plugged converter will give lack of power on acceleration, misfire codes, and egr position codes. Aside from a plugged converter, low fuel pressure can also cause this, but not the EGR code. A plugged EGR passage to the intake will cause EGR codes, but not misfire and no power. Restricted injectors will misfires and no power, but not EGR codes. Suggest having an exhaust back pressure test done.

Visitor Reply:
I forgot to mention that I was a tech for a bit over 12 years but Driveability wasn't one of my stronger suits. I have good exhaust flow. I unplugged the EGR valve and test drove the car a short distance. The problem is still there but not half as bad as it was. It is actually a lot better. Initial acceleration is very acceptable now and will pull hills with very little problem. Still thinking converter? What controls the PCM's instructions to the EGR valve for voltage? Could I have a faulty PCM? What about bad upper intake manifold and gaskets?

Answer:
Mass airflow sensor if any could cause your no power problem. I have never seen an EGR cause the problems you are having. Disconnecting the EGR is just turning it off. IT will come on anytime you try to accelerate, so it sounds like the EGR coming on as it should is just making your problem worse, not causing the problem. Have fuel pressure checked, exhaust back pressure checked. You can unplug the MAF and drive it to see if there is a difference. Be sure EGR is plugged back in. EGR is not the cause of your problem, but when it comes on, it makes it worse. If TPS failed, it should have set a code.

You were right on the money. %766.00 later with a new catalytic Converter in place runs like a top.

Thanks for all your help. I'll jump back on the site and throw some green your way. Appreciate it.

Question:
1997 Pontiac Grand Am 2.4l. Had misfire problem first, replacing the ignition parts fixed problem. But, catalytic converter went bad. Replaced converter and front and rear o2 sensors. Then gas cap for evap leak. Now have a p0420 code. Is it the converter or rear o2 sensor? Or something else? Mass airflow or map sensor? Thanks for your help, if you could respond soon it would really help me. Because I think the shop that replaced the catalytic is trying to get out of warranty. Thanks.

Answer:
Since you seem to be in a bind, i will help now. We were all taking a break for a while, its been busy. P0420 is cut and dry 'catalytic Converter Inefficient' 99% of the time it IS the converter. Have only had 1 bad post cat. O2 sensor cause this in the last 10 years. If the post cat. O2 is bad, it will set a code for 02 sensor, not usually catalytic Inefficient.

Question:
Problem with my 2001/ Pontiac / Grand Am2.4 L. Changed spark plugs. The car intermittently misses under normal driving conditions every once in a while. Changing the spark plugs makes it go away but a day or so later it comes back.

Answer:
If changing the plugs helps, i would look closely at the plugs that were removed. Make sure they all seem the same color. If one is oil fouled, or looks a little greenish or orange (depending on which coolant is in the system at this time) this would indicate an internal engine problem. If one is totally black, this would indicate a rich fuel condition which may be caused by a faulty injector or is more than one is black, then i would suspect a leaking fuel pressure regulator.