What did you do to your NNBS GMT900 Tahoe/Yukon Today?

[RooTBeeRthe1st]

Legit. I don't think I've ever measured higher than mid-60s percentile here.

Now that I have the content handily on my DIC, I regularly see 75% here.
I was far away from a corn station and through a few gallons of gas in with my quarter tank of 75% left and so it's still flushing the gas out.

Also, I am running an actual sensor before the fuel rail. When I had the virtual sensor, it always read somewhere in the 60s until the system failed and started reading way lower causing me all sorts of lean issues.

 

[RooTBeeRthe1st]

As I understand it, it's supposed to adjust on its own based on the measured alcohol content. After you add X amount of gallons to the tank, a relearn is triggered that, IIRC, takes at least seven miles. It's supposed to adjust the fuel and timing tables based on the ALC %. This is why I never ran it before all the engine work which included new O2 sensors. Mine would never read higher than 22% even when I physically tested it to be ~65%. With a fuel that requires more volume just to be on par with E-0, you can only lose power if it's only adjusting for a third of what's actually there. Never mind the lack of timing advance. I've been running corn for a couple of months now (on third tank of it at the moment) and the last two samples taken from the rail have measured within 2% of what my "virtual sensor" calculated. I'd like to go to the track but our ~55° evenings are long gone. The 80+ degree temps we have now would probably more than offset any gains the ~65% ethanol yield. I could run it on a tank of 93 then on a tank of E-85 during the current temps. I'd datalog, too.

The ethanol tables aren't the same as the "high octane" and "low octane" tables. My tuner didn't do anything specific in the ethanol tables. My guess is that they're based on the high octane table and adjust on their own from there, using the knock sensors as "feelers" for spark advance.

Actually measuring the content was how I confirmed that my virtual sensor was messed up previously. I was measuring every bit of 80% and it was reading 20 or 30%.

I should check my next tank, I haven't bothered since I went with a physical sensor. It potentially still could be reading a little lower than it actually is.

 

[iamdub]

Now that I have the content handily on my DIC, I regularly see 75% here.
I was far away from a corn station and through a few gallons of gas in with my quarter tank of 75% left and so it's still flushing the gas out.

Also, I am running an actual sensor before the fuel rail. When I had the virtual sensor, it always read somewhere in the 60s until the system failed and started reading way lower causing me all sorts of lean issues.

I threatened to switch to a physical sensor back when mine was stuck around 22%. When I did the engine refresh and upgrades, I replaced the O2 sensors and got it tuned. I guess the old O2 sensors were the culprit or maybe it was reset after the tune. Whatever it was, it's been much more accurate ever since. I'm still physically measuring the alcohol content at the rail every time I refuel and comparing it to what my PCM is calculating. It's been satisfactory for me so far but I'm still wanting a physical sensor.

 

[iamdub]

Actually measuring the content was how I confirmed that my virtual sensor was messed up previously. I was measuring every bit of 80% and it was reading 20 or 30%.

I should check my next tank, I haven't bothered since I went with a physical sensor. It potentially still could be reading a little lower than it actually is.

I'd like to know your findings! I wish I could find ethanol in the 70s here. At what brand of fuel are you getting your 70-80%?

 

[swathdiver]

@RooTBeeRthe1st @iamdub

Tired O2 sensors is exactly how the alcohol content gets out of whack. They're not bad enough to throw a code but tired enough to not calculate the alky percentage right.

One night we took two trucks to the same pump. My '09 with new O2 sensors and the '13 with 80K miles and original O2 sensors. My truck correctly calculated... Lemme check the logs... Ok, '09 went for 79% and the '13 for 62%. Test tube from the '09s fuel rail was about 80%.

About two weeks earlier at the same station one day apart they were within 2% of each other. The '13 is back on gasoline for the range and it regularly calculates the gasoline alcohol content near zero.

Before changing the sensors in the 2009, it too started calculating the alcohol content incorrectly and similar to the 2013, would calculate in the 60% range while the fuel rail showed 80%.

 

[Doug118]

Picked up some new take-offs for $350 today. Rotors don’t look as new as I thought they would for take-offs but can’t complain for the money on all OEM stuff

 

[iamdub]

@RooTBeeRthe1st @iamdub

Tired O2 sensors is exactly how the alcohol content gets out of whack. They're not bad enough to throw a code but tired enough to not calculate the alky percentage right.

One night we took two trucks to the same pump. My '09 with new O2 sensors and the '13 with 80K miles and original O2 sensors. My truck correctly calculated... Lemme check the logs... Ok, '09 went for 79% and the '13 for 62%. Test tube from the '09s fuel rail was about 80%.

About two weeks earlier at the same station one day apart they were within 2% of each other. The '13 is back on gasoline for the range and it regularly calculates the gasoline alcohol content near zero.

Before changing the sensors in the 2009, it too started calculating the alcohol content incorrectly and similar to the 2013, would calculate in the 60% range while the fuel rail showed 80%.

Actually, I believe it was one of your posts that prompted me to add new O2 sensors to my parts list during the engine work. The term "tired" that you used then and now makes sense. Many sensors can report within range as far as the PCM is concerned, so it never throws a code. It just responds as it's programmed to do, but to inaccurate information.

 

[iamdub]

Picked up some new take-offs for $350 today. Rotors don’t look as new as I thought they would for take-offs but can’t complain for the money on all OEM stuff

That's the fixed caliper stuff, yeah? What diameter are the rotors?

 

[992dr]

My rear is still leaking. I got my new cover, gasket and bolts surprisingly fast but was not expecting the cover to be raw so I blasted it with some Rust-Oleum black, it is now drying and of course it had to start raining. So, I'll hit it with another coat later and hope that it won't be raining tomorrow morning.


Question, how many of you guys have replaced your pinion seal? Any tips would be much appreciated.

 

[Doubeleive]

My rear is still leaking. I got my new cover, gasket and bolts surprisingly fast but was not expecting the cover to be raw so I blasted it with some Rust-Oleum black, it is now drying and of course it had to start raining. So, I'll hit it with another coat later and hope that it won't be raining tomorrow morning.


Question, how many of you guys have replaced your pinion seal? Any tips would be much appreciated.

well the seal can be replaced from the front but most of the time the problem is the pinion is bad, replacing the seal alone has pretty low odds of fixing the problem.
you can drop the drive line and grab it and give a good wiggle if there is any play at all then it's time to replace the pinion and that's a bit of work and it has to be set properly or it will just fail again.
you have to remove the brakes, remove the axles, pull the carrier out and then you have access to the pinion