Emission failure

[H3nightrod]

Hello everyone

Well I’m seeking some advice on what to do with current issues on not being able to pass emission test.

As of now I have done the following work:
engine tune up with new plugs, new exhaust manifold both sides due to leaks, one cat, Evap system, carbon canister, and o2 Sensors.

Before the evap replacement the truck would have a rough start after refueling. I tried to fill up while running and idle was all over the place. This is no longer an issue. However twice I have had the check engine light come on right after refilling and driving a few miles.

The last code I got was PO13B O2 slow response, again right after refueling, however that sensor is new so don’t think replacing will correct this issue. Could it be I need a new fuel cap?

So today I took it to local shop and they suggested to re-flash or update the PCM. Has anyone ever had the update fix an issue similar to this? I kind of don’t see how this would help but then again I’m not a mechanic. I am a little hesitant to do this because I had my PCM tuned about 8 years ago to match 4.56 gears and don’t want to lose this programming.

Any info and advise is greatly appreciated, really need to pass these emission test as my tags have been expired for some time now!!

 

[Nikal]

One thing I’ve learned along time ago with GM is their ECU is very sensitive with the O2 sensors. Aftermarket sensors don’t work well with the GM system. What brand of O2 sensors did you install? Did you replace all O2 sensors, or just one sensor? Best to replace both at the same time. If you did not install the GM or Denso O2 sensors, it could be the sensor & computer are not speaking & timed right. I have a few friends who are GM knowledgable mechanics, and they all say bite the bullet and buy the GM O2 sensors. I would do this before reflashing your computer. Also have a shop with Tech 2 scan tool plug in and watch what’s happening live while running or driving. The Tech 2 is the GM scan tool and is best for diagnostics

Check RockAuto as they have genuine GM parts for allot less than the dealer.

 

[H3nightrod]

I’m guessing it was aftermarket and only one side. It’s a good start I’m going to replace both sides with GM and give it another try.

Thanks again for the help!!

 

[alrock]

Do you have an OBD2 reader to check codes as they come up? Just in case there are other things that pop up. You can get them on Amazon.

Nikal's recommendations sound pretty solid.

And, as always, we recommend having a good battery and good battery terminals in place.

 

[rascole]

Make sure the engine has been running for 15-20 minutes to get the cat hot. If it is still slow, might be the sensor, even new ones can be bad if they have been on a shelf for the last 10 years.

 

[Happy Hummer]

I'm more interested in the refueling and error issue. There has to be something behind this.
Time for a good scanner. You need to be able to read live data stream.
Have you smoked your fuel system and evap system yet?
You really want to be able to watch in real time what the o2s are doing.

 

[H3nightrod]

Ok first thanks to everyone chiming in.

So I started with drivers side and found the downstream O2 sensor was a Japan after market piece, swapped it for new Denso sensor. The upstream was a Denso brand so left it alone.

Right at 100 miles engine light came on again. I only have a FIXD reader and got the same code PO13B O2 sensor slow response. My only guess is drivers side might need attention. I’m going to order both upstream and downstream Denso and swap both. Hopefully this is it.

I have not smoked the evap system as not sure how to do it but will look into it and see what it takes to complete.

Any good scanners out there to recommend?

 

[H3nightrod]

Went for a quick ride and found sensor 1 jumps from 0.12V to .8V constantly. I am assuming this is the issue. My guess would be to replace the remaining 3 sensors to avoid further issues.

Any other suggestions?

 

[rascole]

I believe the upstream is supposed to cycle. You might need more than 100 miles to clear a stored code. Not sure the the number but I think there needs to be a certain start up shut down cycles too.