Fuel economy cause

[Tebbsjeep]

My 06 Dodge with a hemi is getting pretty bad mileage right now. 8.3mpg on this last tank, 230 miles driven and it took 27.55 gallons. That matches up with my overhead console too. It's been like this for months now. I've had the truck a year, and I've only seen double digits in rare occasions.

I don't tow often, and when I do it's light. I drive it conservatively. I've double checked my speedo vs. gps, and it's almost dead on. So I feel my mileage count is correct. I have a coworker with basically the same truck, and he gets 12-15 with his. From what I've read and asked other people with similar trucks, that's about what my truck should get. I expected 12-13 realistically when I bought it.

It runs good, but the upstream o2 sensors are showing temps between 1200-1400 degrees. I've seen them get as high as 1650-ish, which I don't believe is normal. Does that sound more indicative of plugged cats or bad o2 sensors? Both would cause bad mpg. I don't have a check engine light, and I would think if there was an issue that caused a 4mpg drop from what it should be, that it'd pop a light.

Admittedly I'm not very good at diag for this kind of thing, so I thought I'd ask the smarter people here what you think.

 

[STAG]

Have you checked your tire pressures lately with a gauge?

Air filter clean?

 

[Tebbsjeep]

Yes, I try to check that often.

 

[TRD270]

Try a tune up? Maybe injector cleaning? Certainly something up that’s rotten mileage for that truck

 

[Tebbsjeep]

I've done an intake cleaner and multiple fuel treatments. It seems to run ok. That's why I'm stumped. Seemingly running fine and no CEL, but piss poor fuel economy.

 

[RustEoldtrux]

My guess would be one or more injectors are either clogged or damaged, causing over fuelling, which would cause high exhaust temperatures.

 

[Spork]

I'd be jacking it up and spinning tires to see if brakes are dragging on a wheel at that difference. Some difference could be explained with different gear ratios between you and your coworker but it's too much difference for only that.

 

[xjtony]

You can use a long screwdriver to listen and see if the injectors are actually firing. Place the tip of the screwdriver on the injector body and you can hear it fire through the handle, stethoscope style.

 

[Tebbsjeep]

The truck has all new brakes and wheel bearings on all 4 corners, so I don't think it's a drag issue. Wouldn't an injector issue throw a code?

 

[TRD270]

Was also thinking on a drag note. Any chance it’s stuck in 4wd or that the release mechanism is stuck? Not sure what they used those years, I know the prior gen had a janky vacuum disconnect.

 

[Tebbsjeep]

Pretty sure it's not stuck in 4wd. It has the aam9.25 front axle which doesn't have a front axle disconnect. So if it was stuck in 4wd it wouldn't steer very well. Guess I could jack the front end up and verify.

 

[xjtony]

A stuck injector won't necessarily throw a code. The computer thinks it's firing correctly and just tried to adjust the AFR. It will eventually foul the O2 sensor though. I bought 8 Bosch certified rebuilt injectors for the 318 in the buggy, and 4 were bad. They would just fire and stay open. Never threw a code, just used a full fuel cell by Chewy on Pritchett. You could also pull the spark plugs and look for any that may be excessively wet. If one is hung open it probably won't fire very well. Even a temp gun checking the exhaust manifold from cylinder to cylinder can show if there may be an issue there.

 

[jeeper]

I feel the same way exactly about my f350. I drive light footed, and EVERYONE claims better mpg than me.

Then I slowed to 65-70mph instead of 85, and my mpg went way up.

But that was lame. So back to 85.

 

[Tebbsjeep]

The truck doesn't see a lot of freeway driving, and I know that's part of the issue.

 

[Bart]

Good luck with the diagnosis. You just made me feel better about my 9.7 when towing with my 2021 Ram 1500 with a Hemi and eTorque.

 

[Tebbsjeep]

I picked up a temp gun and I'll check the manifolds as suggested.

 

[bryson]

I'll throw my hat in the clogged catalytic converter ring. I think if an injector was to blame, you'd notice it running differently, and I think you'd get a CEL for fuel trims/running rich/lean.

 

[Tebbsjeep]

So I got some more info:

I couldn't reach cyl 3 injector because the oil fill is in the way, but all of the rest of them had the same "pulse" strength and frequency.

The heat shields wouldn't let me get readings on individual cylinders, but I did notice that bank 1 temps were about 30 degrees cooler than bank two, even the pre and post cat temps, per my heat gun. Each cat saw an inlet/exit temp increase of between 60-80 degrees.

The upstream O2 sensors bounce between 0.1-0.8v, and the downstream hold pretty consistent at 0.7-0.8v.

Even though Torque Pro was reading a cat temp of 900-1100 degrees, they measured about 560-600 degrees with a temp gun. I assume the actual gases are hotter then the pipe bodies.

Does that info mean anything obvious to you guys?

 

[Hickey]

Good luck with the diagnosis. You just made me feel better about my 9.7 when towing with my 2021 Ram 1500 with a Hemi and eTorque.

Wow that’s nasty. I averaged 11.4 mpg towing down and back from Sand Hollow.

 

[RockChucker]

Wow that’s nasty. I averaged 11.4 mpg towing down and back from Sand Hollow.

But you have an awesome small and light trailer.