98 5.7L Vortec 2wd STUMPER - P0420/430 Persistant

[shultzee13]

Both cats replaced with new.
All four (4) 02 sensors replaced with AC Delco AFS105 and AFS106 sensors.
No exhaust leaks.
No other codes.
Had engine grounds cleaned, no change.
Clear codes, drive, they comes back.
Have performed PCM reset.

Brand new AC delco spark plugs, wires, cap, rotor, even distributor. Yes I replaced the distributor and the cam shaft sensor.


Without spending an arm and a leg, is my ONLY option to buy the spark plug defoulers and trick the computer?
I notice quite a bit of difference in fuel economy with the computer throws the codes.
How do I determine if the PCM is at fault? maybe it's finally gone bad. I understand that is rare though. I can't figure it out.

Thanks
Eric

[Kudzupatch]

Out of my league but I went looking our of curiosity and found this article interesting. May or may not help you out.

http://www.easterncatalytic.com/educ...he-po42o-code/

[shultzee13]

Excellent article. Thanks.

[speedygonzales]

First understand what the codes mean.

420 and 430 are only the efficiency of the cats. It has NOTHING to do with engine control with regard to fuel. Therefore your attempt to repair the problem by changing the front 2 O2's was a complete waste of money. The front O2s play no role in the monitoring of the O2 health. The rear O2's are only involved in monitoring the health of the cats. Nor does any of the ignition items have any impact on the problem.

Second, this has NO impact on the efficiency of the engine running. It bears no impact on engine fueling. If you disregard the codes, no problem will ensue.

So now we get to the root of the problem, if that is possible via bulletin board troubleshooting.

So a further understanding of the condition that triggers the codes is warranted.
The PCM will command either a rich condition or a lean condition and see if the rear O2s can see the resultant exhaust condition. It looks at the amount of time it takes for the rear O2s to show the change in exhaust gas richness (or lack thereof).

MY first question would be are there any other codes present?

If you assume the engine is at fault causing the problem, there would have to be other codes present. For example, suppose the engine is running lean all the time so that when it commands a rich condition to check the O2 health. The code comes up for not seeing a rich condition. If that were the case, you would have other codes for running lean or front O2 codes.

If you have no other codes, I would suspect a wiring and or connection problem.

Anytime you have a code related to a sensor signal, it's always a good idea to check the integrity of the wiring and connections before simply buying a new sensor.

The simplest thing to do at this point is to monitor the signal of the rear O2s in real time to see if it's swinging. If it's not, start poking through the wiring to see why.

Make sense?

[shultzee13]

I only changed all 02 sensors because I wanted to have Ac DELCO so no one could "there's your problem, your not using Delco." I've heard it more than I ever care to hear it again in the 3 years I've owned the suburban. Lol

Now I am getting PO 420 and PO430. There are no other codes.

Could this be a bad MAF sensor or at least a weak one trying to fail? I have cleaned it. Nothing changes, same problem.
I have excellent fuel pressure.

I have also monitored the live data of the O2 sensors and I see nothing wrong.

[speedygonzales]

If you had bad sensors like a MAF, you would be getting other codes. So no, you don't have a bad MAF.

My suggestion is to have the rear O2s and it's subsequent codes programmed out. I did years ago. My cats melted back in 03 while trailering a car home through the mountains and there was an exhaust leak. I wasn't going to buy $500 worth of cats .

First I used simulators for many years, then when I was having programming done for my future fuel management change, I had the rear O2s programmed out. In your case, simulators may not help.

[speedygonzales]

One other thing, If you see normal rear O2 operation via the PCM. You can assume the PCM is defective. However, I caution you about trying to see real time O2 function and assuming it's normal. One thing you can do without braking the bank is have it reprogrammed. This can correct a programming problem while at the same time, bringing the software up to the latest revision.

This can be done at any AutoValue store. They guarantee the programming so that if the PCM turns out to need replacing, they will put the cost of the programming toward the cost of a new PCM so you aren't throwing the initial reprogramming money away.

On a side note, it's better to use a graphing function on the O2 signals instead of watching numbers jump around. For $35 using a OBDII dongle in your diagnostic port and smart phone with a free app. You can do just that. I do it all the time. You could also have the emissions checked to see if you actually have faulty emissions or just faulty monitoring. This can go a long way to help you determine the problem.

So you should understand by now that the plugs and WETH plug defoulers are will not change the situation.

[shultzee13]

Local shop said they charge $80.00 to reprogram it. The only thing I didn't like that he said was for the 98/99 he didn't think there had been any updates to the Catalytic converter 02's. I know for a fact in the 3 yrs I've owned it, I've never had this procedure performed.
The shop wouldn't really discuss tuning out the cats. I guess that's under the table in Texas I don't know.

I hate throwing ANOTHER $80 at it, if it's not going to fix it. But surely GM doesn't expect customers with older vehicles to be riding around with a "SES" light on all the time.

[hugger6933]

I wouldn't be so sure about the General worrying about your light back in the day Dodge had their lights programmed to come on a 60,thousand and then again at 120. There was a switch besides the instrument panel that was behind a little trim plate. You popped that plate off and flipped the switch it turned off the light.The average driving distance for the normal amount of term time to pay one out then was 60K so they did it to get you to the dealership and thinking about new rides. Sorry so and so's

[shultzee13]

Is there a possibility this could be a fuel system issue? I am reading online about people saying to check the live data of the long term and short term fuel trims as this could indicate a rich or lean condition causing both converters to read this and dump more fuel.

Does anyone have a resource on how to understand the readings of these on live data?

I want to make sure I don't have a leaking injector or a fuel regulator problem.

Don't wanna take off the top of the motor for nothing.
Thanks again for all the help.

[speedygonzales]

You're not getting rich or lean codes.