P0420 Code Issues

[thardy3]

So, I'll start from the top. I've been chasing issues on my 99 2dr, 192k miles, since the beginning of 2013. It started with misfire issues, changed out plugs, wires, rotor, and cap. That did not solve this issue, turned out to be a bad catalytic converter. Swapped both out with weld-in MagnaFlow units and finally put mufflers on it while I was at it (truck didn't have mufflers when I bought it). This fixed the issue for about a week until I hit the highway for longer than 5 miles running 70 or so and it started missing bad. Ended up being a simple MAF sensor swap and she ran good for the next 3+ months. That's when the dreaded P0420 code came up. It was also sluggish in some stop and go traffic situations, kind of felt like a misfire. So I swapped out both rear O2 sensors with Bosch units. SES light has not gone away and it still stutters from time to time.

I've kinda run out of ideas here. Any ideas? Could the high flow cats be causing the issue? Could it be something completely unrelated to the cat system causing the code? Any help is much appreciated!

 

[SunlitComet]

use only delphi or delco sensors do not use bosch.

 

[thardy3]

Something told me that was going to be an issue. I've located the Delco part number for the bank 1 side (after cat), AFS106, do you happen to know the part number for the bank 2 side (after cat)?

 

[thardy3]

Can anyone help me out on my above question? I'm wanting to get sensors ordered for both sides (downstream), just want to make sure I order the right ones.

 

[pkupmanvt]

I don't know if you've fixed this yet, but the rear o2's won't make the engine run rough. The front sensors control fuel mixture, the rear's are just there so the ecm can monitor cat performance for emissions reasons. If the Mass air flow was bad you may have damaged the new cats by pumping too much fuel through them before the maf was replaced.

 

[SunlitComet]

Inaccurate info. The rear o2's do have an effect on the a/f ratio but it is just for fine tuning the mixture for the cats based on what the rears see. And the fronts are the same part number left or right. And a different part number for the rears left or right. so get yourself another AFS106 for the bank 2 post cat section of the exhaust.

 

[thardy3]

I swapped out the two rear O2 sensors and it became clear that my somewhat rough running was unrelated. We discovered that my brake booster was leaking causing a vacuum leak. We replaced the brake booster and she's running like a champ!

Also got the AC fixed, FINALLY!

 

[SunlitComet]

Oh that will do it for sure.

 

[thardy3]

Alright, so my P0420 code and rough running is back. The hesitation as previously described only went away for a day or two but it took upwards of 300 or so miles before the code popped back up. Any other thoughts as to what the cause could be here? I need to try and have these resolved SOON as I have about two weeks before I have to pass emissions here in GA. Any thoughts and suggestions of where I go from here is much appreciated, as I am 100% lost where to go next.

 

[thardy3]

Looks like I'm going to end up dropping her off at a shop next week. Really don't want to, but I'm tired of trying to figure this out. Let me know if anyone has any ideas.

 

[SunlitComet]

Yes, replace the converter assembly and put in all new O2 sensors from delphi.

 

[thardy3]

Replace the converters again? It was done 6 months ago. And I have brand new AC Delco rear o2 sensors that I put in about a month ago.

 

[SunlitComet]

Sorry did not read again all posts back to two months ago. If they are proved to be broken then yes. Take it to a shop and have them do a smog test to get the gas results but abort the test to avoid it being recorded in the dmv database as a failure assuming that it would fail the whole inspection. Have all four O2 readouts presented to you in graph form and verify the fronts go up and down over and over again and that the rears stay relatively stable or almost flat lined. If either rear is acting like the front one of the same side something is wrong with the catalyst or something went wrong with the sensor. However if it has good activity that closely matches the front it should not be a sensor issue. If the cats are not doing there job take them back.

 

[thardy3]

Will do! I'll keep you posted. Thanks for the help.

 

[thardy3]

Alright, so here's the latest.

Last week, had the truck at the trusted mechanic shop. The SES light was not on when I dropped it off, I had cleared the the P0420 a week or so before. Because I had put about 200-300 miles since the last SES light, he scanned the truck and it said "Ready" for emission status. He ran the state emissions and it passed with flying colors. The only issue he could find was that the timing was off, -9degrees. Once he adjusted timing, the truck ran incredibly well. Now for the "but", because there's always a but. On the way home today, the SES light came back on. Scanned when I got home and it's the damn P0420, AGAIN! I am REALLY lost now. It truly makes no sense to me. Any ideas Sunlit?

 

[SunlitComet]

Yes replace the converter set to get rid of it completely until then suck it up with the light, you did get the smog cert after all. Mine is so bad this month I cant reach a ready state and my cert was required a moth ago. I wont get my converter set till later in the month.

One other thing if he used his timing light to adjust your timing he just screwed you. Computer controls the vortecs timing but the crank and cam sensor must be aligned at 0.0° +/- 2.0° anything more you will get the P1430 and maybe if off enough some pinging or misfire/crossfire. Need a scanner to set that using the "CAM_RETARD" PID setting.

 

[pkupmanvt]

I'm not interested in debating who's info is right or wrong, but I've never been a parts changer myself... Throwing parts at a problem without properly diagnosing is a waste of money and resources. The post cat o2's absolutely will not cause a drive ability issue unless they are dead shorted and affecting the readouts from the front o2's. Also, a bad cat won't cause a hesitation unless it's plugged which sounds unlikely in this case. What can and will happen is that a hesitation caused by a rich condition will destroy even a new cat, but replacing the cat will not fix the cause of the rich condition. That MAF problem probably killed the first set of cats by dumping too much fuel through them. I wouldn't replace the cats again right now, I would have a skilled "tech" diagnose the real reason for the engine not receiving the proper air fuel ratio. This isn't going to get fixed in the forum, someone needs to fix it in person, someone capable of comprehending the sensor data the computer is getting and also able to verify the accuracy of said data at the sensor with a multimeter. Good luck, let us know what it ends up being.

 

[SunlitComet]

A multimeter is a horrible way to track O2 sensor activity. I handheld or device based analyzer that scopes it or uses data form the pcm to graph there activity gives a way better idea as to what is going on with them. And according to you in your first post here you are implying that the MAF was the suspected cause of the converter failure and now that it is replaced it would seem to you that it is fixed but you seem to still think that he is running rich when in fact he said the engine was missing but did not give further data as to how or why so are you not yourself trying to say what some of the issue is in the forum yourself? It was never implied to replace the cats without testing them first. It was implied that the the Bosch O2 sensors do get chucked because they have issues with this powertrain such as lack of response speed.

 

[thardy3]

The hesitation seems to have been fixed by the timing being adjusted, with SnapOn scan tool. The guy I'm now taking it to was a long time GM tech and has a 97 z71 with the same motor. At this point, I definitely trust his abilities. The truck is running strong and better than ever minus the SES light. The only code shown is the P0420. Shortly after it came back on, I did notice that it smelt like it was running a little rich while idling in the driveway. I believe something is causing the A/F ratio to be off which is causing the SES light. I now just have to get it back over to shop for a bit so that he can diagnose the real issue. Thanks for all of y'alls input. I will definitely keep you all posted as we work through figuring out what's going on.

 

[83 Bimmer]

Sorry to sidetrack but sunlit, i'm curious about the problems with the bosch sensors you speak of, I personally have never had a problem with bosch sensors, used them on pretty much everything. Is this slow response issue limited to just the vortec engines or have you had this problem elsewhere?