P0420 Code Issues

[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?