Going through more gas then I use to with rich exhaust smell

[Romer]

Seems like when I am driving on the highway I am using much more gas then I use to. I thought it was towing, but after dropping off a trailer in Kansas, the mpg sucked all the way back to Denver. Course I was doing 85-90, but I did the same thing to the Rubicon and got 240-250 miles on the main tank. Today it took me the main and the aux tank to do that.

city mileage seems close to what it use to be.

My exhaust system is fime with a year old muffler and 2 new cats. O2 sensors changed within 10K miles.

Thoughts? Not sure what to check

Ken

 

[Tools R Us]

Is the check engine light on, if so, have you checked the codes?

 

[Romer]

Is the check engine light on, if so, have you checked the codes?

No codes and nothing obvious other than what I mentioned. Idles fine, runs great. Good pickup when I use the SC.

Thats why I am a bit perplexed

 

[landtank]

if there is a fueling issue and no check engine light than it's an O2 sensor/wiring problem. The ECU works on the premise that the O2 feed back circuit is always working at 100%. If there is a problem where there is some error in the readings it simply tries to adjust the fuel to get what it wants.

In your case, if the engine was running at the proper AFR% but the O2 sensor showed a 10% lean condition the ECU would richen the mixture by @10%. This would not give you a code as the ECU is happy with that amount of error but would impact your fuel mileage because you are actually running rich.

In these cases I know only one way to be certain that you have the proper AFR% and that is with an off line AFR% reading by either a wide band sensor or a sniff test.

 

[Eicca]

I have heard that a fuel pressure regulator not doing its job (i.e. too much pressure) can make it run rich...? Correct me if I'm wrong

 

[greentruck]

Of course it smells rich. That's the smell of money burning...

That's not much help, though. Good luck and will be curious what you find out. The bottom of my tank is always getting close somewhere after 250 miles, but if you throw in an aux tank to go that far, too, that is some horrendous mpg, even for an 80.

 

[Nottajeep]

Just throwing this out there, but what kind of gas are you using? This summer change over in the gas industry plus the crap ethanol are really taking a toll on our vehicles designed for "real unleadeded". Haven't tried it yet, but I am told the regular unleaded won't even light on fire.

Also, you might think about some injector cleaner if you haven't used any in a while.
I am trying to stick with Shell and Texaco gas here in TX and alternate with the high octane premium every few fill ups. I am getting 14mpg's right now, but my O2's are bad so I expect improvement when those get changed out.

 

[ardentyota]

You've probably already checked this, but replacing my spark plugs and wires solved my rich burning problem. The POs had never replaced the wires. Apparently 15 year old wires don't carry the current that new ones do... I'm getting .5-1 mpg better than before.

Good luck, and keep us posted!

 

[Romer]

I am running Premium

The spark plu wires were changed about 40K miles ago (5 years)

 

[turbocruiser]

Ken, I think that Rick probably picked the right thing with the O2's ... assuming all the other parts and pieces of the fuel system are strong ... how old are the two sensors? Also running a can of BG44K won't hurt and could help. HTH.

 

[Romer]

Ken, I think that Rick probably picked the right thing with the O2's ... assuming all the other parts and pieces of the fuel system are strong ... how old are the two sensors? Also running a can of BG44K won't hurt and could help. HTH.

Ill try the BG44K, was going to do that anyways. I replaced the O2 sensors about 8000 miles ago with Toyota ones

 

[theRash]

I am probably out in left field with this idea but would it do any good to disconnect the battery for a bit, let the ECU reset and let it recalculate the Oxygen/gas mix again the next few times you drive? Perhaps the towing, playing, and elevation changes etc etc are throwing off/altered the statistics the ECU uses for the right fuel mixture?

Timing out of wack perhaps?
small air/ intake manifold leak?

Just guesses I'm throwing out there.

 

[NaterGator]

Pretty sure you don't have brakes dragging?

Just trying to think outside the box

 

[turbocruiser]

Ill try the BG44K, was going to do that anyways. I replaced the O2 sensors about 8000 miles ago with Toyota ones

Wow, 8000 miles is nothin! Unless you have some pretty serious oil leak into the exhaust then I'd rule out the O2's. As NG stated, might be time to look at other systems altogether.

 

[Tools R Us]

Check the simple stuff, tire inflation, etc.

I would use this as an excuse to get the OBD2 cable for the laptop and download one of the scanner software programs. Most allow you to record fuel trim, etc, and analyze for issues.

 

[60wag]

You don't have the transfer case in low range?

 

[landtank]

Excessive fuel consumption comes down to Leaks, poor fuel management or excessive loads.

On the fuel management side and OBDII scanner is of little help if you don't have something specific to look at which is pointed out in a CEL code. I would get a wide band sensor on it and first confirm you have a fueling issue before anything else.

There was a turbo build recently where the owner had a rich running engine during closed loop. This points to a O2 sensor problem and he opted to install a piggy back to manipulate the O2 signal to get what he wanted. IMO he would have been better off diagnosing the problem and fixing the truck.

And it's not only the O2 sensors, the circuit includes the wiring which is part of the engine harness and passes by the EGR valve like all the other wires. The wires aren't immune to the problems that we all know to happen there.

 

[Romer]

I would think if I had a fueling issue I would see an issue doing city driving. It was at 85-90mph on I-70 comiung back from Kansas after dropping of a trailer

Yes I know you get worse mileage at 85-90, but That was similar to the drive to the Rubicon 2 years ago in speed and conditions. It was windy and that probably was an impact.

Be a while before I take to the open road again on a long trip and then I will likely be towing the heavier Kimberley Kamper.

I put 3 bottles of the Chevron fuel injector cleaner into the two tanks yesterday and I will run that dry and then run BGK44.

 

[landtank]

at those speeds you are definitely in open loop so if it was running rich it would not throw a CEL.

 

[Romer]

I have run through the full tank and aux tank driving a combination of city miles and high speed highway miles after pouring in 3 bottles of Chevron fuel system cleaner. It seems to be back to normal

Could have been the heavy sidewind coming back across Kansas, poor gas I bought there or the fuel system cleaner did its trick

Normal for me is about 12 MPG

I only noticed it on that trip back from Kansas. It was weird, a tank plus the aux would not get me home 300 miles. This week I put on 312 miles and used 26 gallons