Gas mileage?

[Travieso]

i get around 14-16 on my tahoe.. everything stock except exhaust.

 

[SloZ71Hoe]

thats about what i got in mine before i did anything to it. All i had was a muffler... Im waiting on my cam it should be here any day now then i guess ill have to break down and get my freaking wideband lol

 

[xwt572]

Hello. I am having a similar problem with my 2002 Yukon XL. When I bought it a couple of years ago, I got about 18 (US gallons here) mpg on the way home. Gradually it became worse and about a few weeks ago it started stumbling and running rough cold and warm. Replaced the fuel pressure regulator and both front o2's.
Put on the easy xray 6000 and it showed about 2-8 misfires on one single cylinder (6). Before I replaced the goodies it would have multiple misfires (P0300), some up to about 300/500. No everything is running the way it should, smooth and no codes.
Starts much easier too in the morning.
But now the mpg got way worse than before.
Before the trouble started with the o2's and the regulator (and still running normal), I got about 13-15, no matter how long or short the trip was, but on regular gas it would be around 15, on E85 (flex engine) it would run about 13 mpg.
It was much better in the beginning, like 15-17-18.
Fuel filter got replaced about 1-1.5 years ago. I don't really think that would be the problem, but I can't find anything else that could be wrong.
I could put up some pictures of what the easy xray 6000 said when I scanned it.
One thing is way off, the a/f ratio. It is on a steady 10.3, which I know is totally off (doesn't matter if I have the pedal down or at idle). No mods done to this truck.

 

[swathdiver]

Hello. I am having a similar problem with my 2002 Yukon XL. When I bought it a couple of years ago, I got about 18 (US gallons here) mpg on the way home. Gradually it became worse and about a few weeks ago it started stumbling and running rough cold and warm. Replaced the fuel pressure regulator and both front o2's.
Put on the easy xray 6000 and it showed about 2-8 misfires on one single cylinder (6). Before I replaced the goodies it would have multiple misfires (P0300), some up to about 300/500. No everything is running the way it should, smooth and no codes.
Starts much easier too in the morning.
But now the mpg got way worse than before.
Before the trouble started with the o2's and the regulator (and still running normal), I got about 13-15, no matter how long or short the trip was, but on regular gas it would be around 15, on E85 (flex engine) it would run about 13 mpg.
It was much better in the beginning, like 15-17-18.
Fuel filter got replaced about 1-1.5 years ago. I don't really think that would be the problem, but I can't find anything else that could be wrong.
I could put up some pictures of what the easy xray 6000 said when I scanned it.
One thing is way off, the a/f ratio. It is on a steady 10.3, which I know is totally off (doesn't matter if I have the pedal down or at idle). No mods done to this truck.

See if the alcohol content sensor is not reading right. Test your injectors and coils and when were the cats themselves replaced and did you use Chicom ones? If all else looks good, it could be just a worn down camshaft after seventeen years, don't know your mileage.

 

[xwt572]

Alcohol content sensor... That was a new one. Never heard of it before. It doesn't have a muffler anymore. Cats still original I guess. It has no problem revving up to 4-5k and for a 2,600 kg car, it really keeps up with the rest of the traffic, no problems there.
I still have to find a place where they flow test injectors. Not too many places around here in Sweden where they do that.

 

[swathdiver]

Alcohol content sensor... That was a new one. Never heard of it before. It doesn't have a muffler anymore. Cats still original I guess. It has no problem revving up to 4-5k and for a 2,600 kg car, it really keeps up with the rest of the traffic, no problems there.
I still have to find a place where they flow test injectors. Not too many places around here in Sweden where they do that.

You have an alcohol sensor if your motor is the L59. A Tech-2 can perform basic tests with injectors still on the car.

 

[live2pull]

FWIW, i get around 14-15 mpg 60/40 highway city mix. i can get 16 mpg if i have a light foot and do more highway

 

[xwt572]

Hello again. I have had an auto X ray 6000 connected to see what is happening while driving. This alcohol sensor thing must be working, since the reading for af ratio changed almost instantly when I changed fuel E85 to 95 octane just a few days ago.
I did find a wire to the cylinder 1 coil to be in a bad shape (bad repair from a previous owner?). Haven't taken a closer look to get the thing out so I can fix it properly yet, but that might be one reason to why it all of a sudden can start a misfire.
The behaviour changed now to a scenario where the whole left bank starts to misfire under load (going up hill with a trailer).

Results from Auto Xray:
Readiness motors complete. NO
Fuel sys 1 closed loop
Fuel sys 2 closed loop
Load value 1.5%
Coolant temp 89°C (192F)
Short term fuel trim 1 -4.0 to 2.0%
Long term fuel trim 1 0.0 to 2.3%
Short term fuel trim 2 -1 to 2.5%
Long term fuel trim 2 2.4 to 0.8%
Map 35 kPa (doesn't a 5.3 have a MAF???)
Engine rpm 560
Vehicle speed 0
Ign timing advance 20°
Intake air temp 21°C (70 F)
Air flow rate 4.7 to 5.7 Gm/sec
Throttle pos 0%
O2 1 sensor bank 1 0.060-0.780
Short term fuel trim 1 0 to -3%
!!!O2 sensor 2 bank 1 0.075-0.800 slowly changing
!!!O2 sensor 1 bank 2 0.095 to 0.780 mostly on the higher side
Short term fuel trim 1 0 to -3%
!!!O2 sensor 2 bank 2 0.050 to 0.4490 slowly changing
OBDII require OBDII (CARB)
PTO not active
Batt volt 14.0 volt
Throttle sensor 0.58 volt
Front o2 sensor 0.070 to 0.690 mostly on the higher side
Rear o2 0.098 to 0.600 mostly on the lower side
EGR pos 0.00 V
Fuel tank pressure 1.15 volt
Throttle pos 0.00 volt
EGR valve open 0%
Trans oil temp 39°C (102° F)
Camshaft retarder 0.0°
Start up coolant temp 30° C (86° F)
Canister purge solenoid 17%
Fuel trim cell 17, drops to 2 when revving
Desired idle 550
Desired EGR 0%
Baro press 99 kPa
!!!A/F ratio 10.2 (E85), which according to me means richer than normal (I had a Diablo sport program installed but i lost the diablo sport programmer thingy. Can't find it anywhere)
Engine run time 2260 sec
Knock retard 0.0°
EGR test count 0
!!!EGR pos error 100% (is this correct?)
Total misfires 12
Cyl 6 (10) and cyl 7 (2)
Long term fuel trim 125, sometimes 128
Rich7lean Lean/rich ratio 0

Stuff that really changed here when I picked up a trailer a few days ago, was that under load all of a sudden the whole left bank started misfiring.
Cyl 1 3 5 7 with counts up to 3000-4000 for cyl 1 and I think 7, the others less but still way too much, like 300-600.
Long term fuel trim went up to about 145
Rich/lean lean/rich ratio changed to 1
Bank 2, nothing at all, 0 counts

Parked, turned off the engine, let it sit for about a half hour with the batt cable off, reconnected batt cable, cleared fault codes after I checked (no codes registered???), started the engine and let it run for about 30 seconds and started driving again.
No misfiring at all, 0 on all 8 for about 15 minutes before I had to go up a hill again.
Under load and revving up to about 2500-3000 rpm, right after same crap again, 1 3 5 7 misfiring.
Same procedure all over again, shut off engine, check codes (nothing), wait 30 minutes, started, no misfires.
Yesterday I put in 95 on an almost empty tank and after about 10 minutes af driving and resetting the auto Xray, the AF ratio was on 13.2 (still too rich).
Drove all the way home, same route no trailer, no misfires at all.
When I got home and let it run on idle, some misfiring started on 2-3 cyls, where the highest number was 17 on cyl 7.
Long term fuel trim was about 125 all the time, rich lean ratio on 0.

 

[swathdiver]

I did find a wire to the cylinder 1 coil to be in a bad shape (bad repair from a previous owner?). Haven't taken a closer look to get the thing out so I can fix it properly yet, but that might be one reason to why it all of a sudden can start a misfire.

The behaviour changed now to a scenario where the whole left bank starts to misfire under load (going up hill with a trailer).

Bad head gasket under load? Do the simple checks first, grounds, plugs, wires, wiring, coils, fuel pressure, fuel rail condition, etc. and then do the compression test. What do y'all think?

 

[xwt572]

Will test this when I can. Thanks for now. As mentioned, one wire looks suspicious, the wires to the number 1 coil are not the way they should.