Horrible MPG

[Drew907]

So I have a 2001 Tahoe 5.3 4x4. It had a tuff life till I bought it. It’s got 180,000 miles and holding up well. My issue is my gas mileage is horrendous. Getting between 7-9 mpg in town. Now I live in AK and it’s 10-15* daily this time of year so it gets idled a lot to warm up. In the last 2000 miles I’ve changed
-plugs and wires
-oem fuel pump and new filter
-oil change with quality oil and filter
-intake air filter
-cleaned throttle body
-big 3 upgrade for other reasons
-new battery
Right now I have a check engine light on for a bad car on bank 2. On my scanner it’s showing that the front o2 sensors are acting normal. At idle it has a bad hiccup that feels like a fuel issue or vacuum leak. I’ve looked over the intake manifold with a fine toothed comb and found no leaks. Fuel pressure is right on the money at idle and with rpm.


I’m stuck on what to check next. I don’t mind throwing parts at it. I want this rig perfect. In the summer we put on lots of highway miles during fishing trips.

 

[Mudsport96]

If you have alot of idle time thats possibly the reason. My wife lets ours idle long enough when i hop in it the readout shows 9ish mpg. So my guess is thats a big part of your deal too. While i would check that o2 code and fix it, l dont think bank 2 will have much affect on mpg

 

[OR VietVet]

Same type of recent problem with my old 2002 LT. Idled bad in gear and a stutter from a stop. Bad sensor. May also be old enough that the cats are failing too. This is a problem with an older NBS with 180k miles. Cats old enough to not be efficient, no matter how many new sensors are installed. Replaced all 4 sensors and problem solved. I would also be worried about this: https://www.rockauto.com/en/moreinfo.php?pk=1298772&cc=1371620&jsn=2512. There are a couple of choices, so check the application at RA for the correct one.

 

[wsteele]

O2 sensor issues can force the engine to stay out of closed loop. Closed loop allows your engine to trim fuel flows very precisely.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics, please.

 

[Fless]

O2 sensor issues can force the engine to stay out of closed loop. Closed loop allows your engine to trim fuel flows very precisely.

^^^ THIS. And get a reading on your short- and long-term fuel trims, both banks, with a scanner. Idle and 1500 RPM. They can tell you a lot.

 

[Wylie_Tahoe]

Bank 2 would the right side of engine, as in for cyls 2-4-6-8. What code says the o2 is bad?

Have you cleaned the MAS? Just dont blow it with compressed air.

 

[exp500]

Fuel pressure regulator, and/or relay.

 

[BentleyArnage]

^^^ THIS. And get a reading on your short- and long-term fuel trims, both banks, with a scanner. Idle and 1500 RPM. They can tell you a lot.

 

[BentleyArnage]

60k plus on the sensors? Replace them. They do all sorts of things that don't set codes. Just trash them like spark plugs. It's been a common thread with O2 sensors since the beginning.

 

[BG1988]

So I have a 2001 Tahoe 5.3 4x4. It had a tuff life till I bought it. It’s got 180,000 miles and holding up well. My issue is my gas mileage is horrendous. Getting between 7-9 mpg in town. Now I live in AK and it’s 10-15* daily this time of year so it gets idled a lot to warm up. In the last 2000 miles I’ve changed
-plugs and wires
-oem fuel pump and new filter
-oil change with quality oil and filter
-intake air filter
-cleaned throttle body
-big 3 upgrade for other reasons
-new battery
Right now I have a check engine light on for a bad car on bank 2. On my scanner it’s showing that the front o2 sensors are acting normal. At idle it has a bad hiccup that feels like a fuel issue or vacuum leak. I’ve looked over the intake manifold with a fine toothed comb and found no leaks. Fuel pressure is right on the money at idle and with rpm.


I’m stuck on what to check next. I don’t mind throwing parts at it. I want this rig perfect. In the summer we put on lots of highway miles during fishing trips.

that is the problem bad car on bank 2...



7-9mpg sounds right for 4x4 even in the snow I got ****** MPG on the hybird model....


i got down to about 12.5MPG that was in 3-4 inches of wet snow...


Snow causes a huge amount of drag so much i did not even have to use the brakes very much as the SUV came to a complete stop just by down shifting and Regen...



I suggests getting a radiator blanket or something to cover the grille vent ( have it open like 50% ish)

 

[OR VietVet]

The problem is that too many times people think O2 sensors are all the same. What got you here? Get the GM original sensors and be done with it. Aftermarket of any kind has not been researched as well as the GM OE sensors. They warranty that long for a reason. I had a a sensor problem and went with OE and know these sensors will outlive me.

 

[Capsalot1]

The problem is that too many times people think O2 sensors are all the same. What got you here? Get the GM original sensors and be done with it. Aftermarket of any kind has not been researched as well as the GM OE sensors. They warranty that long for a reason. I had a a sensor problem and went with OE and know these sensors will outlive me.

I have a scanner tool, what’s a good reading for O2, MAF, etc?

 

[rockola1971]

If you have alot of idle time thats possibly the reason. My wife lets ours idle long enough when i hop in it the readout shows 9ish mpg. So my guess is thats a big part of your deal too. While i would check that o2 code and fix it, l dont think bank 2 will have much affect on mpg

I hope you are thinking bank 2 is POST CAT 02's. One of them is. But bank 2 refers to the passenger side cylinders/exhaust and that 02 (Pre Cat) is the input for adjustment of rich/lean for the injectors on that side (bank). It is very important for this 02 to be working correctly. Same for Bank 1 02.(Pre Cat).

 

[rockola1971]

I have a scanner tool, what’s a good reading for O2, MAF, etc?

If any of those sensors output a "bad reading" the PCM will catch it and set a code. Look at both banks (pre cat) o2 sensor data and compare bank 1 to bank 2. Should look similar. Look at both banks post cat also. (But keep in mind that the Pre Cat o2 sensors are the only ones used for inputs to adjust air/fuel ratio). Post cat o2's are just there to tell you that your cat(s) are bad and WILL NOT affect how the engine runs.

Check to make sure you dont have any brakes dragging. Caliper sticking, broken springs on emergency brake shoes, etc. Check emergency brake adjustment. If you are using overdrive, verify that tranny is actually shifting into overdrive (count the shifts and dont confuse torque converter lockup around 40-45mph as a shift). Check fluid levels in rearend and Tcase.

 

[Capsalot1]

If any of those sensors output a "bad reading" the PCM will catch it and set a code. Look at both banks (pre cat) o2 sensor data and compare bank 1 to bank 2. Should look similar. Look at both banks post cat also. (But keep in mind that the Pre Cat o2 sensors are the only ones used for inputs to adjust air/fuel ratio). Post cat o2's are just there to tell you that your cat(s) are bad and WILL NOT affect how the engine runs.

Check to make sure you dont have any brakes dragging. Caliper sticking, broken springs on emergency brake shoes, etc. Check emergency brake adjustment. If you are using overdrive, verify that tranny is actually shifting into overdrive (count the shifts and dont confuse torque converter lockup around 40-45mph as a shift). Check fluid levels in rearend and Tcase.

Rear caliper s we’re replaced due to sticking so that issue is fixed. She’s two wheel drive, what’s an easy way to check rear end fluid level?

 

[swathdiver]

Rear caliper s we’re replaced due to sticking so that issue is fixed. She’s two wheel drive, what’s an easy way to check rear end fluid level?

Pull the plug in the differential cover and the fluid should be level or just under (no more than 3/8th of an inch) the opening.

 

[Capsalot1]

It should also be noted, it was sitting in a driveway for five years and the mechanic ran the old gas through it. I put a can of seafome in and filled with premium. It puffed black smoke for a bit then cleared up. It’s running good now with exception of excessive gas usage.

 

[Capsalot1]

Pull the plug in the differential cover and the fluid should be level or just under (no more than 3/8th of an inch) the opening.

It should also be noted, it was sitting in a driveway for five years and the mechanic ran the old gas through it. I put a can of seafome in and filled with premium. It puffed black smoke for a bit then cleared up. It’s running good now with exception of excessive gas usage.

 

[Capsalot1]

Rear caliper s we’re replaced due to sticking so that issue is fixed. She’s two wheel drive, what’s an easy way to check rear end fluid level?

Also, can the pre and post O2’s be swapped for troubleshooting or cleaned?