P0420 means if all of your O2 sensors are good, then you have a bad CAT.

And this code doesn't really mean anything if it is running poorly.

You need to get a mechanic to monitor O2 readings using a proper OBDII tool and diagnose from there.

 

I have one of those tools. The cat is new magnaflo. But this issue has been going on before the replacement of the cat.

 

Your B1S1 and B2S1 O2's are the ones to watch, they must change fast and bounce from above .5 to below .5 , If it stays above .5 you are rich, below .5 you are lean. When both are bouncing happily above and below .5 then move on to your LTFT (Long Term Fuel Trim) should have one for each bank.

The LTFT's should be close to zero, they go above zero when it needs more fuel than normal (O2 says it is lean) and of course below 0 when it needs less fuel (O2 says it is rich).

The STFT (Short Term Fuel Trim) has the same purpose but reacts quickly to signals from the O2 sensors and updates LTFT when the values are large enough for a period of time.

Example: LTFT around 5.0, and STFT around 2.0, the engine is running lean and fuel is being added to compensate.

Example: LTFT around -10, and STFT around -2, the engine is running rich and fuel is being subtracted to compensate.

Readings around 0 are normal, but LTFT of less that 3 either way is ok too.
Note there are separate fuel trims for various RPMs and load conditions, so concentrate on idle first then to a higher rpm and do more testing.

Also your Injector Pulse Width Bank1 and Bank2 should be very close to the same, a large difference here means left and right are running very different.

Hope some of this helps, Good Luck.

 

here is everything that was going on with my Blazer at the time the CEL came on.

Fuel SYS1 CL
Fuel SYS2 CL
Calc Load% 10.5
ECT F 199
STFT B1% 7.0
LTFT B1% 0.7
STFT B2% 7.0
LTFT B2% 0.7
MAP 13.5
Eng RPM 1840
Veh Speed 42
MAF (lb/min) 2.0968

the reader can not actually read Live. Thought it could

 

Were these readings taken while it was running rough? Looks like driving down the road at 42 of course. What readings at idle and or when it is rough?

At idle, are your front O2 sensors changing rapidly?

 

I do not have a way to monitor the O2's while at idle.

These reading were taken while I was driving and when the light came on. It was running rough when the light went off. I reset the codes and took it for a 20min drive with hills and stops and 45mph top speed to see if the code came on and it gave all the stats of Blazer the instant the CEL came on.

The code says Bank1 so I am guessing it is the Bank one senor since all the reading I get seem fine. Not sure about the MAP or MAF readings.
I checked oil and not coolant in it. I took some down and had it tested. Oil change was like 100 miles ago. No coolant loss at all and nothing on top of intake.

 

The only code you posted, P0420 is not significant for this problem, you need to check with a capable OBDII scanner to monitor the O2 readings and Fuel trims then diagnose from there.

 

Yes I know. It is a generic code. I was hoping posting all the live feed data while the code came on may rule out something or give a clue from there. I do not have access to anything to monitor the O2 sensors. With it saying Bank1 does that mean "possibly" a bank1 sensor? I'm half tempted to just take the bank1 sensor out and clean it and see if it helps. The injectors were just dumping fuel due to clogged injectors. So I am thinking maybe the O2 sensors are just coated with junk.

 

I just posted this on another thread and someone here has already mentioned it, but check your egr. I have had some of the same issues and to me, it sounds like the egr has a piece of carbon holding it open part way and probably not opening or closing right anymore. Take it off and try cleaning it and see if it helps...good luck.

 

well do. Thanks. They are expensive to replace. Anyway to test them?