p0420/misfire

I have a 2000 Z71 5.3 89k miles and am getting p0420. First I switched the down stream O2 sensors right for left and reset the code. It came back so I switched the up stream O2 sensors right for left and the same code came back. It has something to do with the left bank of cylinders. The tricky thing is that it feels like I have a misfire at idle. In drive with my foot barely on the brake, the truck will sort of bounce forward like one cylinder is missing. No misfire codes have ever come up though. Compression is real close to even on all cylinders. No sign of misfire under any other conditions than barely creeping forward.

Welcome to AF, start by doing a site and/or google search for this code plenty of good info out there.

I have a 2000 Z71 5.3 89k miles and am getting p0420. First I switched the down stream O2 sensors right for left and reset the code. It came back so I switched the up stream O2 sensors right for left and the same code came back. It has something to do with the left bank of cylinders. The tricky thing is that it feels like I have a misfire at idle. In drive with my foot barely on the brake, the truck will sort of bounce forward like one cylinder is missing. No misfire codes have ever come up though. Compression is real close to even on all cylinders. No sign of misfire under any other conditions than barely creeping forward.

p0420 is cat efficientcy driver side is unaceptable........try swapping the cats see if problem changes just kidding.... replace the driver side cat....is where your going.... but why did this occur ?????you just buy this vehicle any history?????

I have had this problem for about 8 months but I drive a company truck most of the time and only drive mine a few times a week. I have had the truck less than a year. It does have dual exhaust after the Y pipe. I found lots of stuff about the cat going bad, but I am wondering about the funny miss. If an injector isn't working right, and I'm not getting a complete burn on one cylinder at idle would that make the cat angry and through the code? What about a weak coil pack? I just don't want to through money at it till it's fixed. Especially when it has no effect on drivability. By the way, you guys have already saved me money, time, and headaches on other little problems because of the info I have found here. Thanks

If an injector isn't working right, and I'm not getting a complete burn on one cylinder at idle would that make the cat angry and through the code? What about a weak coil pack?

What happens is you don't get a complete burn and it overloads the cat and it fills up with carbon and stops working or doesn't work good enough. The computer sees too much activity on the downstream O2 sensor and sets the code. A weak coil could cause it, a leaking injector, bad plug/wire/both could all cause it. If not done yet, I'd do a full tuneup on it. You're getting pretty close anyway, adn that could be the cause. If that doesn't fix it, check the resistance of fuel injectors and coils. If one is much different than the others, replace it. I don't know the specs off hand, but they should be close to the same. If none are electrically bad, do a cylinder balance test. Unplug one injector and see if it makes a difference in how it runs, plug it back in. Repeat on the other 4 cylinders on that bank (P0420 is bank 1). If you find one that makes no difference or little difference, you've found the cylinder. To determine if it is the coil pack or injector, just swap the coil with another one and see if it changes cylinders. If it stays on the same cylinder, the injector is bad.

I have had this problem for about 8 months but I drive a company truck most of the time and only drive mine a few times a week. I have had the truck less than a year. It does have dual exhaust after the Y pipe. I found lots of stuff about the cat going bad, but I am wondering about the funny miss. If an injector isn't working right, and I'm not getting a complete burn on one cylinder at idle would that make the cat angry and through the code? What about a weak coil pack? I just don't want to through money at it till it's fixed. Especially when it has no effect on drivability. By the way, you guys have already saved me money, time, and headaches on other little problems because of the info I have found here. Thanks

if at idle it is missing try the PCV r/r this and check for vacuum lines leaking..... if intake manifold has leak this could acount for bank1 driver side running rich.... if all plugs looked the same then thats out.....because your not original owner it is possible some componet failed that caused this cat to now not remove pollutants to a level that pcm accepts..do not use carb cleaner or other chemicals that damage rubber to find vac leaks as then you will need intake manifold repair for leaks......

Will WD-40 work to check for vacuum leaks? Also, doesn't the resistance of the air fuel mix increase as more air and fuel are added? A weak spark should show up at high engine loads. Right? Any how I have a project for this afternoon.

Thanks

Will WD-40 work to check for vacuum leaks? Also, doesn't the resistance of the air fuel mix increase as more air and fuel are added? A weak spark should show up at high engine loads. Right? Any how I have a project for this afternoon.

Thanks

if removing the plugs and they all look the same and have a light tan color and the gap is correct [platinum falls off tip] then its just a bad cat....as you already checked o2 by swapping and you checked compression... and yes if you had a bad plug or coil or wire i would expect a miss under load not idle thats why i suspect some vacuum leak possibly or maybe something like the IAC as this needs cleaning every 50,000mi on my engine...the plug wires should read 500-600ohms......on coils do like jr said compare resistance all should be same or close...

I had a very similar problem on my 2002. The only real difference is I was getting a P0300 code as well as P0171 and P0174 which are lean codes and a random misfire. The fix for mine was intake gaskets. I am guessing that because you have considerably less miles than I do your gaskets are original and probably no leaking THAT bad to throw the codes I got. However if they are leaking at all it could cause a lean condition on one side and probably cause carbon build up in the one cat. From what you said it would be bank one with the leak. Intake gaskets are not too expensive to replace, it cost me around $80 in parts and $150 in labor. Of course you could do it yourself if you have the time and the ambition... Good luck!