Car acting weird

[Fredless]

I searched on EGR and the P0420 Code.

My car ever since the P0420 Code was first thrown about two months after carmax installed the cheap 3" cat on my car, has had a WOT knock or pinging sound erratically, especially when it is cold.

The SES light will come on for about 3 weeks, then after that, will stay off for about a month. This has been the cycle since about April of this year. Well I know I have an exhaust leak at the cat because the idiots decided to put a 3" cat on the stock piping, and I've had it welded shut and it still springs small leaks, so I've said screw it for the past few months.

The car just hit 100k, and nothing to my knowledge has been replaced on the car as far as sensors or accessories go. After researching, found out it could be a number of things causing this.

However, I read some EGR thread and a fubar'd EGR could cause detnonation (probably where the WOT knocking sound is coming from).

Since the O2 sensors are expensive, as well as the EGR crap, I don't want to go replacing all of that and it fixes nothing.

1)If I have to replace the EGR, how many pieces are there? Just one?
2)Can the EGR be cleaned?

Any other input on the problem? Fuel filter has been replaced, religious oil changes, have the AC Delco Iridium plugs that were swapped in at 85k (NGK TR55ix's basically), spark plug wires changed at 90k (autozone cheapy brand, fixed P0300 code) and the cat was replaced at about 76k right after I bought the car...so it has around 25k on it. Seafoamed a few months ago as well.

[HBHRacing]

first 2 things.. one. you must fix any leak that falls before an 02 sendor or you will get false readings and codes. second if it's a high flow cat it might be setting the code even if it is working correctly. if your pinging at WOT I would be looking at a fuel problem first, an ignitin problem next..

[98Camaro3.8]

Originally posted by Fredless:
because the idiots decided to put a 3" cat on the stock piping

Stock cat is 3".

[HBHRacing]

^ yes, but also depends on where they cut it. also the nice flat part on the top of the 3 inch merge pipe that likes to leak..

[Fredless]

Its cut so that they have to fill the gap where the 2.25" slides into the 3" coupling with a ton of ****ty welds.

So its basically just going to act weird when there's a leak before the after cat O2 sensor? Looks like I have an excuse to buy the flowmaster LT1 catback now.

[98Camaro3.8]

Originally posted by Fredless:
So its basically just going to act weird when there's a leak before the after cat O2 sensor?

After cat sensor does nothing to performance. It's only purpose is to warn you if the cat isn't working like it should (like if you had a high flow cat). The car will get weird readings from that sensor, but it won't do anything besides setting an SES (possibly P0420).

[HBHRacing]

I cut the merge pipe and then I cut RIGHT after the cat where it was still 3 inches. That way the cat literaly slid right in and very light clamp pressure held it. Only problem I had was the flat spot on the merge pipe leaked, I had to weld that.

Any air leak can set a code. anything in front of the rear 02 will not effect performance except for disturbing flow. any leak in front of the front 02's will drive the car rich.. I would take care of that leak just to be done with it


I would still be looking at fuel and ign for the ping. Contaminated fuel could be doing it as well. if the EGR was sticking it would be running rough at idle.

[Fredless]

It does kinda idle rough someitmes at idle, but then smoothes itself out relatively quickly.