The Check Engine light 5

Hi,

I went to Autozone to get my check engine light diagnosed and they were pretty broad in what the problem could be. I cant afford to get a mechanic to check it out just yet, but i wanted to see if anyone had any ideas on the list of problems they gave me, as I dont want the car to die on me because I left it too long.

98' Lumina 3.1 146k

They said it could be

1. Misfire - although the car runs great and I'm sure I would know if it was misfiring, I dont hear anything strange.

2. Bad Cat - I got the car an emissions test and they mentioned the cat, but I'm not sure if they were just generalizing on my certificate, it just said OBDII fail. The engine light was on when I took it for its test though.

3. Large vacum leak - I'm not really sure what this is so I dont know what to look for, again, the car runs fine and I dont notice any problems.

4. Worn engine - That sounds really general to me, the AZ guy couldn't really elaborate, a worn engine sounds real bad, but how do I check that?

5. Oil leaking into cylinders - I have had to fill up the oil but i'm not sure if thats whats causing it.

The actual code was P0420 and it read: the PCM has determined that the catalyst system efficiency for bank 1 is below the threshold for the current engine operating conditions. (bank 1 identifies the location of cylinder 1, while bank 2 identifies the cylinders on the opposite bank)

I dont know if this is the actual problem or just a spiel that comes with the code.

Any help would be appreciated.
Thanks

That code is an Emissions problem, and you not passing emissions kind of helps prove the point. this may be useful for you.


# P0420, P0430 Catalyst Efficiency
Code P0420 indicates that the exhaust gas exiting the catalytic converter is too similar to the exhaust gas entering the converter. A faulty or overloaded converter due to an unbalanced air/fuel mixture can cause this condition.
# Check the exhaust system for air leaks or holes rusted through. Any outside air that leaks into the exhaust can go through the cat as lean exhaust and hurt its efficiency.
# Rap on the converter with a fist or a soft mallet and listen for anything loose or rattling inside. If the catalyst element is cracked or broken apart then the cat will need replaced.
# You may want to test the O2 sensors for proper operation. Because these sensors tell the computer about the performance of the converter, malfunctioning O2 sensors can set this code. Verify that the sensors are faulty before replacing.
# There may be another problem causing the engine to burn an excessively rich or lean air/fuel mixture. This could overload the cat and ruin its efficiency as well.
# Common causes include incorrect fuel pressure, an EGR system malfunction, an MAF sensor malfunction, intake or vacuum leaks, incorrect cam timing, a bad PCV system, misfires, injector problems, cooling system problems, a restricted air filter, a head gasket leak, or a high oil level.


i pulled that off a quick google search. hope this helps

Thanks, I'd hope its the cat, does anyone know the cost of getting a new cat and also is it difficult for me to do myself, or should i used a qualified mechanic?

cat converter's are very expensive usually. Last time I bought one for my old car, it costed just over 500 bux. And They can be a realy PITA to put on. Especially if the exhaust is rusty, there is just no chance of getting those bolts out without breaking them. What I would do is narrow down the obvious. Change the air filter. Like NeonKnight said. Although he says that it could be caused by an exhause leak, thats highly unlikely, cause you would more than likely hear that expacially if it was before the cat converter. I beilieve I've heard that certain places can recondition "cadillac" converters. Although this usually only pertains to people who's cat converters are plugged up. Yours more than likely is not. I really know nothing on testing O2 sensors, but if you were to take it to a qualified shop, I'm sure they'd be able to help ya sort out your problem. As for Vacuum leaks, If you had a major one, you would notice your car's acceleration would be poor, it would use a lot of gas, and if it were bad enough, you'ld be able to actually hear the hissing coming from your engine as it was sucking in air. I myself dont believe that it has anything to do with running too lean/rich. These OBD2 cars today will be ably to tell that its running too lean/rich and will trip a code for that. If thats the only code you got, check out that cat converter, and your Oxygen sensors.

Thanks for the update, I had the air filter changed just 2 months ago. I dont think its a vacum leak with things you described, the gas milage is good and so is the acceleration. I dont notice a specific hissing sound. If it was the cat (which I'm sure it is now) how long can I drive around with a bad one before i really need to do something with it?

im guessing until you pass smog? hahaha :)

There are several ways to check the cat before spending your money. One is to check the inlet vs outlet temp of the cat with an infrared thermometer, should be 100 degrees hotter at the outlet. This checks efficiency to confirm or deny, in part, the cat is operating. This assumes all other operating sensors and misfire issues are within normal parameters. Another test is to get a pressure gage on the o2 sensor in front of the cat and check back pressure, shouldn't be over 1.5 psi, this checks for blockage. p0420 can be a complex diagnosis, some manufacturers even have software updates to correct that code.

I'll try and check that out. Sounds like this is going to be a pain in the ass. Thanks for the info fellas.