BlazinREDZ28

Hi all,

Found a nice v6 that I'd like BUT it's setting a P0420 Code. It also has a slightly rough idle seems worse after it runs for a while. There are no other codes though. The cat was replaced already, will be checking the o2 on that side to see if that's the problem. The idle prob should not be caused by an o2 sensor prob, correct? It has 135,000 miles on it, one owner, and very well maintained, BUT I don't think the plugs/wires have ever been changed. If they have, he can't recall it, or just took it in for maint and it was done with out him realizing. Maybe a "just do whatever it needs & I'll pay for it" kind of thought on his part. This is a VERY nice car, looks nearly new, just has these issues.....any thoughts?
Thanks,
Kim & Seth
Hoping to have another in the driveway......

SupplySgt.

Could be the 02 sensors setting off that code. could be some oil burning as well. and if that's the case that could be causing the rough idle. I would say the plugs and wires are causing the rough idle and it is possible that it could cause the code. but the 02 sensor shouldn't cause the rough idle. at least i can't think of any reason why it would. Another thing to look at is the EGR valve. that'll cause a rough idle as well. I really don't think it's anything that's not fixable based on what you've said and as long as you can fix it it'll be a good car for you

2000GTP

Try switching O2 sensors from bank to bank and see if the code follows.

BlazinREDZ28

I am going to talk to my aunt today and she if she will let me swap the o2 sensors and see if the code follows the sensor or stays the same. That way I will know if the problem is the cat or the sensor. I was just curious about the rough idle. I haven't had many dealings with the v6s. Did not know if there was something that frequently caused a rough idle with them or not and after all the crap with my Z I don't want to get another car I will have to do all kinds of work to before I can start driving the freakn thing.

2000GTP

Could just be that it is in need of that tuneup. You would be surprised the kind of problems that neglected plugs and wires can lead to. Is the car misfiring at all?

BlazinREDZ28

okay everyone. We bought the car I changed out the spark plugs and wires. I started the car and noted no change in the idle. I did notice a strong odor coming from the exhaust. Tommorow I am going to borrow my friends scan tool to see what is going on.Thinking it may be an O2 sensor that has died causing the computer to go into fits. My aunt just had the cat. replace about six months ago. Any suggestions. Thanks

2000GTP

Have you looked it over any exhaust leaks? Is the odor like a rotten egg smell?

byrons1502

it could be a lot of things. vacuum leak,injectors(common),coil pack(common),valve springs(common) try shorting out a plug wire at a time by backprobbing the wires at the coil with a test light grounded to the negative side of the battery and see if thge miss stays or goes away. if you isolate the problem to one cylinder swap the coil pack with a diferent on.(example= makes no change with cylinder 2 shorted swap coil 2/5 with 1/4 and see if it moves) if it does not swap injectors bank to bank and notice the diff. stays the same run a compression test. if ok pull a valve cover and check for broken valve springs(extremely common)
testing the cat would involve a scan tool(not a autozone special)

BlazinREDZ28

Okay, i climbed under the car a little while ago to change the post cat o2 and liked to craped. Who ever welded up the cat welds like a dirt dober. I had my wife crank the car and found three leaks on the weld before the cat. Do you think this could be causing my false lean condition? Also I am pulling those crappy duralast wires off tommorow bringing them back and getting some delphi wires. The car seemed to run worse after I installed those pieces of crap.I should have known better than to buy them but I that will not happen again.

2000GTP

Seeing that the exhaust leaks are taking place after the 02 sensor, I don't see that giving you a false lean condition.

byrons1502

if the leaks are close after the o2 it can still give that code. if you put duralast wires in i bet you bosch plugs in also. if you did remove them and by some delco double platinums. if electricity runs through it or it moves stay away from the zone. most(90%) of the runs rough probs or no start cold probs after someone does a tune up is either cheap wires or bosch plugs.

BlazinREDZ28

Found an exhaust leak (actually 3) right before the cat, had those welded today....ran a teeny bit better. Then here came the DREADED Service Engine Soon light AGAIN!!! Had cleared it yesterday with a scan tool. Car is back to the way it was running with a roughish idle. Noticed it's using a little more gas than I think it should too since the service engine light came back on again. So, maybe that O2 behind the cat? I have one, but it's a Bosch (thinking maybe a diff brand would be the way to go here), not installed yet. Was waiting to see what welding the exhaust leaks would do. I'm taking the Autozone plug wires off tomorrow, and getting the Delco. I'm getting frustrated here, the rough idle and the Code P0420.., still recovering from TONS of blood boiling episodes of problems with the z28!

2000GTP

The driveability issues wouldn't be related to the post cat sensor, it is there stictly to monitor the catalyst efficiency.

BlazinREDZ28

Went to a friends shop yesterday and put the car on the ob2 scan tool again. Found out that the aftermarket cat. is not holding enough back pressure. The rear o2 is working over time. The rough idle they said was from dirty injectors. I put a can of lucaus injector cleaner in the tank. Guess we will know soon if it worked or not.

2000GTP

I don't know how good the fuel system treatment will work, an actual pressurized injector flush might be a better solution. As for the cat, since it is a high flow cat, it is most likely giving off excess emissions, but it shouldn't be a backpressure related issue. The rear 02 sensor only monitors the catalyst efficiency, it in no way is responsible for engine operation, that is the front 02 sensors job.