Terrible 8 mpg 1996 silverado

[great white]

Bank 1 and 2, sensor 1 is what is used for fuel trimming.

You sensor 2 readings can either be converter issues or the sensors gone bad. Volts high indicates it is seeing a rich condition, no response indicates it is pooched.

If it is the convertors, it is possible they are contributing to the poor fuel mileage through excess exhaust restriction. It doesn't take a lot to choke back a few MPG's

I would expect your truck to be somewhere around 10-12 mpg in city winter driving.

A few things like extended warm up times, more time in 4x4, low tire pressures or driving style can knock and easy 2 mpg off those numbers.

My suggestion at this point would be to "tough it out" until winter is gone.

Then, when you don't have to warm the truck up before driving, deal with cold temperatures (IE: I'm talking about the engine taking longer to get to operating temp) and slippery crappy roads check your mileage.

The 13-15 mpg you se guys quoting is summer mileage, not winter.

For example: my 6.5 diesel gets 16-19 mpg in the summer. My last fuel log revealed 11 mpg. It's been marching steadily down to that point as winter has gotten a firm hold on us. now that we're in the dead of winter, it will bottom out around that 11-12 mpg mark. It will start going back up when the warmed weather arrives. Happens the same way every year.

It's just "the way she goes"....

 

[kamokevin]

I thought The post cat o2 sensors were just for emissions giving readings for just evap not affecting fuel

Whoops, I read it as pre-cat not post-cat. But yes the post-cat sensors only check catalytic efficiency. I would check your injector spider assembly to make sure it's not leaking any fuel

 

[99'Subourbon]

Tire pressure is good and my air filter I cleaned and put back in the air gauge says its good I just did the rear wheel cylinder and checked all my brakes nothing seems to be hanging up it starts right up every time no problems

Tire Pressure is good is misleading. Good for 1 tire, is god awful for another. What tires are you running, what is the COLD PSI at?

For example; For model year 99, our trucks come with p245/75r16 @ 35 psi, or a load rating of 2200~, after truck adjustments (1.10), like 2105 load rating per tire (if I recall correctly).
If you are running LT285/75R16s, your cold PSI should be at 38-40~ PSI. LT tires take more pressure to get the same load rating at P tires. I air up my tires to 40 PSI. Ride suffers a small bit, being both an LT tire and higher PSI, but I average a combined 14.5 mpg out of my Suburban, which is quite a bit heavier.

 

[heavychevy350]

Ok thanks for the advice maybe I'll replace all four and see if that affects anything and true great white I'm sure this freezing cold weather isn't helping with short trips

 

[poncho62]

When you are saying in town driving, what do you mean?....All stop and go, a shot up the interstate in town, etc?

I have much the same truck as you and when around town (small town)....my mileage is just as bad as yours....If I go to my daughters, which is 1 1/2 hr steady drive, it gets much better.......Cold weather is also a killer.

 

[thunderstruck]

trimmed the lip off the throttle plate

Could you elaborate on that? Like did you grind down the rod the plate pivots on?

[edit] forgot the Vortecs had those restrictors on the plate. That may be contributing to the problem, but not the main cause.

 

[NacIK]

I had a similar problem with mine. I was getting 10 mpg in my 'hoe. My ball joints were blown so I replaced them, replaced my shredded tires, and got an alognment. After that I was up to 12 but my truck still felt like I was dragging 10 tons behind me. I had also noticed later on that week that I could not turn full lock without the axle locking up and my 4wd was hardly letting me move at all when engaged. I replaced the molasses is both axles with M1 diff fluid and now my truck almost glides on the pavement with just a touch of the skinny peddle. I now have 4wd and get 17 mpg. I was shocked and pissed off for not thinking about it years ago.

I will think twice about taking a dunk in the next mud pit I see!


Sent from my iPhone using Tapatalk

 

[heavychevy350]

40 psi in my Goodyear dura tracks And by in town I mean the short trip to my school and back 5 miles one way and the throttle plate had that small curved lip on the inside of the plate I ground that down flat

 

[michael hurd]

Goodyear Duratracs are not going to be the fuel mileage champion... something like a Michelin LTX MS/2 rib tire would give you better fuel economy, however marginal.

Cold weather, cold oils in the differentials, transfer case and transmission, plus short trips is going to drop your fuel mileage quite a bit. Larger than stock tires can also reduce your fuel economy. Taking a trip through a drive through in the morning can also drop your mileage.

 

[heavychevy350]

What could cause the sensor to be reading a rich condition?