P0420 and P0430 - Need Help Diagnosing

“Sitting for quite some time” seemed to affect both the Explorer and the Expedition….
Which led me to believe that ethanol may have been a contributing factor.

And

You absolutely have to see the downstream and upstream sensors simultaneously and preferably in a “two graph” voltage mode.

Plus: watching both catalyst temperatures comparatively in two graph mode gives you an idea of the performance of one VS the other.

In my case both vehicles had all catalysts within a very close temperature range throughout RPM and driving modes which also prompted me to replace the downstream O2 sensors.

stilbo said:

One more kernel of thought….
If an injector were to have been contaminated to the extent that it would not close sufficiently after the intake cycle and allow fuel to enter the cylinder during an exhaust cycle, backfiring would be a result. And even if said condition is intermittent at most, if repeated often enough the ECM would see said rich condition via the O2 sensor and that can be thought to be a failing catalyst.

Click to expand...

Not commonly because then the primary or upstream O2 would see the overly rich condition vs when the converter is lazy, the 1st O2 reports normal and the 2nd is out of whack.
On standard fuel injected engines where fuel is injected into the intake runners, there would be no backfire from extra fuel and it wouldn't enter on exhaust stroke as intake and cyl would just already be to rich.
Shouldn't be any backfire etc just dumping rich exhaust out that cyl and it that side exhaust manifold straight into that side converter.

stilbo said:

“Sitting for quite some time” seemed to affect both the Explorer and the Expedition….
Which led me to believe that ethanol may have been a contributing factor.

And

You absolutely have to see the downstream and upstream sensors simultaneously and preferably in a “two graph” voltage mode.

Plus: watching both catalyst temperatures comparatively in two graph mode gives you an idea of the performance of one VS the other.

In my case both vehicles had all catalysts within a very close temperature range throughout RPM and driving modes which also prompted me to replace the downstream O2 sensors.

Click to expand...

Just saying that most DIYers don't have the specific info.
They have 0420 or 0430 so left of right side below threshold.
90 percent of time they think it could be a bad 02 but 95 percent of those times...it doesn't go away with O2 replacement.
Garages don't care to fully diagnose it even though they have the equipment as they will go for 2 converters and 2 sensors for the money.
I've seen so much money wasted on O2 sensor replacement that didn't keep the light out.
Yours was not the most common situation.

Thank you everyone for all the replies.

The last misfire that I had was back in November of 2019, but it was very intermittent and wasn't constant. I don't think that misfire could have caused converter problems, considering it has been 3 1/4 years since the misfire happened.

I figured out how to bring up the Bank 1 Downstream O2 Sensor voltage on my scan tool, and it was imitating what the upstream was supposed to read (Which indicates a bad converter). However....I noticed that when I was on a bumpy road, the voltage would dramatically go up and down, and at some points read 0.00 Volts. Not long after that, the sensor showed 0.00 Volts for about 6 seconds, and then came back online and voltage was back to moving erratically.

I am starting to think that it might be an electrical issue fooling with these sensors, It does not make any sense that the O2 Sensor would lose power while driving, and that bumpy conditions would change voltage. Possibly a short circuit somewhere?

I will have to inspect the wiring soon, possibly corrosion on connectors?

I was also looking at short trim fuel trims for banks 1 and 2, and they were jumping between -3 and +3. It is that normal? I think 0 is a perfect mixture. I presume that it would always be a little bit negative or positive, never perfect.


Thanks
- Joseph

Quick update...

I tried using some Cataclean in the system, and it clearly worked MPG-wise, but still gave me the P0420 & P0430 codes.

I could've get above 14 MPG on the highway, but after I used Cataclean, it jumped to the usual 19-20MPG. The Cataclean was clearly working, but something is odd.

Any tips?

Thanks,
-Joseph

Hello Everyone,
Found out that the problem is that both catalytic converter's are dead. Turns out that it was from my driving habits when the vehicle was used at very low speed for many months. It looks like replacement cats have fixed the problem.

Thank you for all your help
-Joseph