GeorgeB’s 2013 Suburban LTZ “Fin”

[iamdub]

Noticed an odd behavior.
1/4 tank of fuel
Coasting down from 50mph into a right turn with a yield. When I get back on the the throttle I experience a hesitation to accelerate. Once the trans figures out it need to downshift the truck goes as it should.

Seems to only happen at or below 1/4 tank.

I am going to try to record a snapshot of the fuel data tomorrow before I fill up. Not sure if I can record the trans data at the same time or not.

Mine would hesitate on hard acceleration with ~1/4 tank or less. Got worse the lower the tank level got. I ran the fuel down to 1/4 tank to make dropping it easier for replacing the pump. When I was finished and started it to back out of the shop, I had maybe 1/16th of a tank. The problem was my fuel level sensor had failed the last 1/4 of its travel and the PCM was estimating the remaining fuel remaining by injector duty cycle, run time, etc. So, when I thought I had 1/4 tank remaining, I was actually on fumes and running it dry on the hard accelerations when that little remaining fuel sloshed to the back of the tank.

 

[George B]

Mine would hesitate on hard acceleration with ~1/4 tank or less. Got worse the lower the tank level got. I ran the fuel down to 1/4 tank to make dropping it easier for replacing the pump. When I was finished and started it to back out of the shop, I had maybe 1/16th of a tank. The problem was my fuel level sensor had failed the last 1/4 of its travel and the PCM was estimating the remaining fuel remaining by injector duty cycle, run time, etc. So, when I thought I had 1/4 tank remaining, I was actually on fumes and running it dry on the hard accelerations when that little remaining fuel sloshed to the back of the tank.

I was worried this might be the case for me but I consistently refuel at 1/4 tank and almost always put in around 20 gallons. I only ever notice it when I am coasting and then get back on it. It might actually be the trans trying to find the right gear. If I mash the throttle it downshifts and takes off.

 

[iamdub]

I was worried this might be the case for me but I consistently refuel at 1/4 tank and almost always put in around 20 gallons. I only ever notice it when I am coasting and then get back on it. It might actually be the trans trying to find the right gear. If I mash the throttle it downshifts and takes off.

The 6L80's trans shifting is known to get confused. But I can't connect the fuel level and that, so I'm at a loss. Your symptoms sounded similar to mine in text so I had mention it in optimism. I rarely ever refuel completely so that was one reason why my issue snuck by for so long.

 

[George B]

The 6L80's trans shifting is known to get confused. But I can't connect the fuel level and that, so I'm at a loss. Your symptoms sounded similar to mine in text so I had mention it in optimism. I rarely ever refuel completely so that was one reason why my issue snuck by for so long.

I remembered your fueling issue which was why I suspected that. First thing I did was log the fuel pressure and watch the trims. Everything looked fine. Of course it didn’t act up on me with the scan tool connected tho.

I ran two bottles of Techron through it on the last tank and have been running on E85 for the last three months or about 12 tanks full now.

Next on my list is to clean the TB and disconnect the battery for a bit to make it relearn a few things.

 

[iamdub]

I remembered your fueling issue which was why I suspected that. First thing I did was log the fuel pressure and watch the trims. Everything looked fine. Of course it didn’t act up on me with the scan tool connected tho.

I ran two bottles of Techron through it on the last tank and have been running on E85 for the last three months or about 12 tanks full now.

Next on my list is to clean the TB and disconnect the battery for a bit to make it relearn a few things.

Don't forget to clean the MAF as that affects trans shift characteristics as well.

 

[George B]

Don't forget to clean the MAF as that affects trans shift characteristics as well.

And a new air filter…

 

[Sparksalot]

Don't forget to clean the MAF as that affects trans shift characteristics as well.

How so?

 

[iamdub]

How so?

Part of how the PCM calculates engine power for it to tell the trans what to do with that power. The MAF sensor is how the PCM reads the air going into the engine. The engine is an air pump, so X grams per second plus other factors equates to X power (I think it calculates it as torque, to be specific). Anyway, it references that, the throttle angle, the RPM and the engine load (MAP sensor) to determine shift pressures and points.

 

[George B]

With this thing its like the trans needs to downshift two gears when I get back on it and it is just slow to do it. Its not consistent except in a specific intersection under exact circumstances.

 

[George B]

The thing I hate the most about how this truck drives is the throttle lag. I wish @BlackBearPerf could tune more of that out for me. I love my tune otherwise.