Persistent P0420 and P0430

[5StarCustmSolutns]

If this is about the 2011 truck in your signature, it has NO physical flex fuel sensor unless someone added one. It's all done by the PCM/ECM calculations.

If you know for certain that the actual alcohol percentage is low, reset the long term fuel trims and reset the alcohol percentage.

Is this a flex fuel truck? If so, I wonder if the fuel sensor has failed. If it thinks there is that much alcohol in there, it's going to dump in extra fuel trying to keep 14.7:1 ratio. I know when I ran a tank of e-85 in my 2008 denali (non-flex) it ran like a champ but I got lean bank codes after a number of miles due to it not being able to satisfy the fuel rate needed. No lasting damage as far as I can tell.

As a test, I wonder how it would behave with a tank of e85, or a higher blend to get to the 60% mark it thinks its seeing. Just a thought

Yes it is flexfuel, w/154,xxxmi - 123,*** by me. Always hesitant to say 100%, but I'm fairly confident they abandoned the physical fuel alcohol sensor beginning w/the 2006.5 models. GM went to the V-FFS multi sensor algorithm. I have, I guess you would say, "settled on" the exact thing you described as happening. Thinks it's really 67% FA% in the tank so it pours the fuel to it trying to reach 14.7.
However, of all the testing and experimenting I have done, I have not put one drop of e85 into it. As I read your words I started smh and thinking "why have I not tried that??", just to see what happens? I think the answer to that(speaking about myself only) it would have to be tunnel vision and/or ego. TV from only being able to put so much time into it per garage session, it's 2am before I could even sit down and answer these. Ego being something I learned was holding me back as a designer/builder 5-6yrs ago(slowly won that battle). Part of the ongoing growth process. Plus I just read about ego being referenced on an HP Tuners forum yesterday. Thanks for the suggestion....going to try e85 next and will report results

If this is about the 2011 truck in your signature, it has NO physical flex fuel sensor unless someone added one. It's all done by the PCM/ECM calculations.

If you know for certain that the actual alcohol percentage is low, reset the long term fuel trims and reset the alcohol percentage.

Yes sir that's how I understand it to be since 2006.5. An algorithm that formulates FA% from the readings of multiple sensors. [In hindsight it would've been for others trying to help me had I elaborated more on the hypothesis I'm working from now and how I got here. I just started quoting the better sounding repliers and made this conglomerate message. Sorry....I was already behind my target departure time and got a little too excited when I read the level of the follow-up questions and the advice on this subject in two other threads.]
Not sure of all the sensors used but: MAF, MAP, IAT, Evap Purge(?), Fuel Press, O2's, Knock(?), and possibly others. Sorry eyes getting heavy.
Read about it first here: https://www.chevelles.com/threads/gm-tech-alcohol-fuel-sensor-question.849586/ third post down.
This may be a sign of how little info is out there on this: I've watched that exact video. He has a few other on this same subject. He also tests the gas in a couple. I have reset my FT's and my FA% at least 3 times the first time while putting 3,5,8 random gallons of E0 into the mix. And again when I decided to run 3 straight full tanks of E0. Only then did all FT's and MPG restore to normal OE spec. But within minutes of filling up with 87 again, everything was back out of whach.....I watched the FA% go from 3-6-17-28-49-73 in the first few miles
There's also been a TSB on subject saying the solution was to take it into dealer for reflash, but I've read several owners say it didn't help them only drained their wallet$?
I'm excited to see if e-85 might straighten it out? It makes no sense but neither does what's happening.

THanks for your suggestions

 

[5StarCustmSolutns]

I also met the parts Depot Mngr for one our local Chev dealers at a party last fall. He became a little intrigued by this and asked a few of his service guys and either they refused to give him the answer w/o my bringing it in -or- they were stumped also??
I feel like if I could pin down exactly what sensors the V-FFS uses I could go through them one at a time and get to bottom of it?

 

[Fless]

I have reset my FT's and my FA% at least 3 times the first time while putting 3,5,8 random gallons of E0 into the mix. And again when I decided to run 3 straight full tanks of E0. Only then did all FT's and MPG restore to normal OE spec. But within minutes of filling up with 87 again, everything was back out of whach.....I watched the FA% go from 3-6-17-28-49-73 in the first few miles
There's also been a TSB on subject saying the solution was to take it into dealer for reflash, but I've read several owners say it didn't help them only drained their wallet$?
I'm excited to see if e-85 might straighten it out? It makes no sense but neither does what's happening.

A couple of suggestions, then. If this is happening all the time then it might be worth having the computer calibrations checked for updates and having a search done for any TSBs. Flashing the ECM shouldn't be all that pricey, either at a dealer or an independent shop that's familiar with GM programming.

Any time enough fuel is added (I think 3 gallons?) the fuel/alcohol composition is recalculated. This can take a bit of time and it's recommended that the truck be driven for several miles (7? 10?) without shutting down the engine. Pretty sure @swathdiver has posted up the specs at one time or another; maybe he can clarify. Shutting off the engine before the calc is done can cause issues with the percentage.

 

[Fless]

Here's a Service Bulletin about it: https://static.nhtsa.gov/odi/tsbs/2014/SB-10069954-0335.pdf Not sure if this is the latest.

 

[5StarCustmSolutns]

A couple of suggestions, then. If this is happening all the time then it might be worth having the computer calibrations checked for updates and having a search done for any TSBs. Flashing the ECM shouldn't be all that pricey, either at a dealer or an independent shop that's familiar with GM programming.

Any time enough fuel is added (I think 3 gallons?) the fuel/alcohol composition is recalculated. This can take a bit of time and it's recommended that the truck be driven for several miles (7? 10?) without shutting down the engine. Pretty sure @swathdiver has posted up the specs at one time or another; maybe he can clarify. Shutting off the engine before the calc is done can cause issues with the percentage.

Thanks you for the suggestions. I broke protocol yest morn and quoted the several members that I felt had the best replies on the three threads I read, and did it all in one long post. 1. I know better than to make small novel posts tagging multiple people because they're confusing and people don't have time to sift through them. 2. I know better than to ask for answers after only reading three posts. Both are just bad strategies on forums.

Somewhere in that quagmire of a post I mentioned finding that same TSB and also finding several people that followed it's direction and then vented their frustration over paying to have their pcm updated and still having the incorrect FA% issue.

Last night I ended up reading on here until way late, which is what I should've done before posting anything. My excitement for answers got the best of me yesterday morning. There's a lot of info on this subject on this forum. It may need to be gleaned from a discussion on EVAP purge canisters etc. but it's here. I need to make/take the time and find it.

It was two years ago this month when this started and it was two years ago last month when my Torque Converter shudder started(which I haven't even looked up on here since joining). These two "conditions" have forced me to learn more than I ever thought I would need to know about computer controlled modern automobile systems....and have motivated me to buy an HP Tuners interface and a dedicated laptop for it and for the Power Commander software that's on my Grizzly. The Autel I have has been great to learn with but doesn't have many bi-directional features, which are required to diagnose and fix a lot of this stuff. This concept wasn't even on my radar two years ago when this started lol.... I've enjoyed the education process though.

I'll post results of how my LC9 reacts to the e85 tank.....and when I finally determine the responsible party for this FA% mess I will share it's name with all lol.

Baffles me why so few follow up and share their results after asking for and receiving guidance! First recognized this a few years ago trying to save $4900 bones by changing the front driveshaft on my wife's Mercedes....don't get it

 

[swathdiver]

61%, 67%, 73%, 81%, even when putting 4-5 gal of E-0. Last summer I ran 3 straight tanks of E-0 gasoline and reset my FT's and my FA% at first fill-up and EVERYTHING went back to normal for the duration of that gas.

It is perfectly normal for the percentages to move around along with the LTFTs after refueling. If you find that your truck is registering too much of an alcohol content when it should be 10% or less my issue was old oxygen sensors. They still functioned fine in their primary job, moving about like they should but started inaccurately calculating the alcohol percentage until they were replace with new OE sensors.

 

[5StarCustmSolutns]

It is perfectly normal for the percentages to move around along with the LTFTs after refueling. If you find that your truck is registering too much of an alcohol content when it should be 10% or less my issue was old oxygen sensors. They still functioned fine in their primary job, moving about like they should but started inaccurately calculating the alcohol percentage until they were replace with new OE sensors.

Thanks for reply.. Changed O2 sensors in June '21 and everything was back to normal for about 2 weeks, I even posted about prob being solved on Av forum....and then it went right back to rich condition and large negative numbers on LTFT.. However I did buy cheap sensors!?!?

One thing I have yet to do is pull the intake and check gaskets and manifold bolts....I've read a couple places about the gaskets causing similar symptoms and about the manifold bolts underneath the intake being loose.... You would think my propane leak test would've found a prob there though?

 

[swathdiver]

Thanks for reply.. Changed O2 sensors in June '21 and everything was back to normal for about 2 weeks, I even posted about prob being solved on Av forum....and then it went right back to rich condition and large negative numbers on LTFT.. However I did buy cheap sensors!?!?

One thing I have yet to do is pull the intake and check gaskets and manifold bolts....I've read a couple places about the gaskets causing similar symptoms and about the manifold bolts underneath the intake being loose.... You would think my propane leak test would've found a prob there though?

Yes, your propane leak test would expose a leaky intake gasket. I kept tightening mine up for years and finally just replaced them. The high trims at idle lessened for a time but started creeping back up again. In my case, I wonder if the plastic intake is simply warped from age.

Aftermarket oxygen sensors do not play nice with the computer system and cause problems almost always.

 

[5StarCustmSolutns]

Yes, your propane leak test would expose a leaky intake gasket. I kept tightening mine up for years and finally just replaced them. The high trims at idle lessened for a time but started creeping back up again. In my case, I wonder if the plastic intake is simply warped from age.

Aftermarket oxygen sensors do not play nice with the computer system and cause problems almost always.

It very well could be in both of our cases? or has a hairline crack that may only become a "vacuum leak" under load? Somewhere in my multi-quote quagmire of a post I wrote that I felt like mine was possibly only leaking under load, when the engine was twisting and torquing around in sequence with my foot??

Side note, I've spent too much time in the last 3mos looking for a good used diesel to pull a compact track loader with(commonly called a Bobcat here lol, no matter the logo, just a Bobcat). During the search I started noticing a trend in the straight on from behind pics. On hundreds and hundreds of trucks the drivers side rear bed corner is a little lower than the passenger. Brought this up at a local engine builders shop one Fri eve in Nov with a few savvy customers and the full staff present and nobody had an immediate answer why?? I'd been thinking about it since prob mid-Sept and suggested it may be that the frames are slightly torqued from years of the motor slamming down on the drive side of the cross member? After a lengthy discussion about gas tank and driver weight, road camber, repeated closing of driver door, etc.. we settled on the engine torque theory.

So I wouldn't rule out a warped intake or some form of crack/gap separating under load??

 

[swathdiver]

It's certainly possible, there are lots of connections on the intake too that can leak or develop cracks. I almost replaced mine but held onto the $200 or so. If the trims run wild again I'll just replace it with a new one.