Towing with a 305 V8?

[CheemsK1500]

TLDR: Your catalytic converters or O2 sensors are bad.

My 2011 Suburban used to get 15-16 around town and 20 on the freeway. 10mpg loaded pulling a 6k lb trailer at 70mph. The mileage just started to slowly drop out and now it is down to about 10mpg around town, 13-15 on the highway, and 8mpg towing. I pulled my hair out trying to figure out what was going on... and then I saw some posts about catalytic converters on the Gen IV LS platforms causing loss of fuel mileage and how to see if your cats are bad using HP Tuners and datalogging the O2 sensors. Sure enough.. did a run and looked at the sensor feeds and there was no #2 O2 sensor switching after the initial warmup. They basically loaded to rich after warmup and stayed there. This stayed the same even after replacing all 4 O2 sensors with GM OE sensors. When logging all four sensors, you SHOULD see the rear o2 sensors switching about 20% of the rate that the front sensors are switching.

I have a new exhaust from headers all the way to exhaust tip going on this next weekend with new flowmaster high flow cats going on. I'm hoping I should get all of that mileage back. I also ended up disabling the flex fuel because the bad cats were causing the virtual flex fuel algorithm to decide that I had anywhere from 15-45% ethanol content in my ~10% content max standard gasoline. It was causing it to put WAY too much timing in and also run pig rich, which was also a part of the problem.

Hmmm, I have tried swapping 02 sensors in the past to no avail. I never thought about the cats or timing adjustment. I will have to investigate this further. Thanks.

 

[Bextreme04]

@Velder Also keep in mind whatever the trucks legal GWVR is will not change after you make changes to it. If it's only got (for example) 2K left for towing and your running around with a 5K trailer you could get slapped with some serious issues if you were ever involved in a accident your fault or not. So another something to think about.

Just wanted to point out that GVWR does not include a trailer. The only amount of weight from the trailer that counts towards the GVWR of the vehicle is the tongue weight or the amount of weight transferred to the vehicle by a weight distribution hitch. The trailer weight DOES need to be within the manufacturers rated tow limit or the published GCWR(Gross Combined Weight Rating) of the vehicle.

Just as an example, my truck(1980 K25 Pickup) has a GVWR of 8600lbs and a manufacturers tow rating of 6,000lbs, so my GCWR would be 14,600lbs.

 

[Bextreme04]

Hmmm, I have tried swapping 02 sensors in the past to no avail. I never thought about the cats or timing adjustment. I will have to investigate this further. Thanks.

Just as an update to this, I was going to swap the exhaust to the new long tubes, new cats, and bigger exhaust to get ahead of the engine swap I'm doing soon... but I don't really have the time and it isn't a priority. I remembered seeing a post somewhere about somerune running the Cat cleaner liquid and it really helping clean their cat out, so I thought I'd give it a try.

The suburban has been down to 12.4mpg average with mostly around town driving. It was down to less than 1/8th tank of gas and I needed to run some errands in it, so I figured I'd do the cat cleaning and see what I got. I stopped off at Autozone and picked up a bottle of the Catacleen for ~$20 and dumped it in(it says to put the whole bottle in to less than 1/4 tank of gas and drive for 10-15 miles) and then romped it around town and on the freeway for about 10 miles, then got off the freeway and filled it up with Costco gas. Reset the average fuel meter and now the average has shot up to ~15mpg. Its getting ~20mpg cruising at 70mph on the freeway again and averaging about 14mpg around town like it used to. I'm going to try running another bottle or two through it for the next couple tanks of gas and see what happens, but I can definitely confirm that dirty cats will negatively affect the fuel mileage on the Gen IV LS motors.

 

[SirRobyn0]

Just wanted to point out that GVWR does not include a trailer. The only amount of weight from the trailer that counts towards the GVWR of the vehicle is the tongue weight or the amount of weight transferred to the vehicle by a weight distribution hitch. The trailer weight DOES need to be within the manufacturers rated tow limit or the published GCWR(Gross Combined Weight Rating) of the vehicle.

Just as an example, my truck(1980 K25 Pickup) has a GVWR of 8600lbs and a manufacturers tow rating of 6,000lbs, so my GCWR would be 14,600lbs.

Right and that is a much better and through explanation than I gave. Thank you for that.

 

[overdrivestepside]

Yesterday towing in my 305 C10 with functioning ESC ignition, 2.73 2wd, 4 speed overdrive new process transmission. It worked great!

 

[Velder]

Thank you @overdrivestepside ! I really appreciate it. How much do you think that load weighs?
I have decided not to use the C10 as my main tow vehicle, but I am embarking on a cross country move, and am considering making it tow the welding rig, because my new truck, (new to me I should say, It has over 200k on it) will be towing a 36 foot gooseneck. Maybe I should go ahead and wire the C10 up for towing. Any thoughts anyone? Would any of y'all trust your C10s to tow 2000 miles in 4 days from Texas to Montana?

 

[SirRobyn0]

Thank you @overdrivestepside ! I really appreciate it. How much do you think that load weighs?
I have decided not to use the C10 as my main tow vehicle, but I am embarking on a cross country move, and am considering making it tow the welding rig, because my new truck, (new to me I should say, It has over 200k on it) will be towing a 36 foot gooseneck. Maybe I should go ahead and wire the C10 up for towing. Any thoughts anyone? Would any of y'all trust your C10s to tow 2000 miles in 4 days from Texas to Montana?

I would hop in my truck and drive it across the country tomorrow if I needed to without a second thought. And I'd tow across the country if I needed to as well. Some of my feed hauls are 100+ miles towing 6K. I would not want to tow that much weight across the country, just because it's slow on the hills, but I'm sure she'd do it and I'd do it if needed. The biggest thing is how you have taken care of the truck and the weight of the welding rig.

 

[overdrivestepside]

The package was about 3500 lbs.