Exhaust Brake problem...

[n7ki]

I just installed a Bully Dog Watchdog gauge monitor system on my 2007 6. 7L Dodge with the manual transmission and when monitoring the fuel usage gauge, I noticed that the usage would increase when I have the exhaust brake on and let off on the gas pedal. I a very short time the fuel usage would jump up to 6 to 8 mpg. I believe this is not right and also noted that on a trip with my travel trailer in tow going from 1200 ft in altitude to 7200 ft, my mileage was approximately 10mpg. On the return trip, the mileage was also 10 mpg. with the exhaust brake on. I believe I should have gotten a 2 to 3 mpg improvement. I have no idea what could be causing this and could use some help. I used to be able to say that this truck ran good down hill but now that is not even true.



Thanks,



John B.

 

[jelag]

The exhaust brake on the 6. 7 engines turns the vanes in the turbocharger backwards. . I owned a 08 5500 and to be honest never much paid attention to the fuel flow... but I think your trying to tell us you think the performance is down. .

One of the key factors with this turbo is that you leave the exhaust brake on. . so that the mechanism that moves the vanes can't carbon up and drag or stop functioning... when it functions correctly it moves from one end of the spectrum to the other with the exhaust brake engaged. .

I would assume if the vanes are not moving full cycle that its from carbon but I'd expect a code from low boost... remember back when some of these turbos were cleaned at the dealership, mostly from lack of the full cycle. . they drilled them and injected a chemical...

Leave the exhaust brake on... and let it cycle... see if it straightens itself out...

 

[HBarlow]

I don't know anything about the Bullydog box or have any interest in knowing. It's not clear to me whether you are reading average fuel consumption from the truck's overhead display or the magic box but if you are reading the overhead display it is a cumulative not instantaneous reading.

There is no way the engines turbocharger which provides exhaust braking is causing increased fuel consumption unless as Jim suggested above the turbo is sooted and binding which would be setting check engine lights and codes.

 

[Jim W]

I just installed a Bully Dog Watchdog gauge monitor system on my 2007 6. 7L Dodge with the manual transmission and when monitoring the fuel usage gauge, I noticed that the usage would increase when I have the exhaust brake on and let off on the gas pedal. I a very short time the fuel usage would jump up to 6 to 8 mpg. I believe this is not right and also noted that on a trip with my travel trailer in tow going from 1200 ft in altitude to 7200 ft, my mileage was approximately 10mpg. On the return trip, the mileage was also 10 mpg. with the exhaust brake on. I believe I should have gotten a 2 to 3 mpg improvement. I have no idea what could be causing this and could use some help. I used to be able to say that this truck ran good down hill but now that is not even true.



Thanks,



John B.

John,

I take it that the truck is stock and all the Bully Dog is doing is monitoring the engine and other parameters through the OBDII port, correct? If this is the case, than I would not consider the fuel usage reading at all from the Bully Dog.



There are lots of variables that effect fuel usage from one mile to another and the monitor will only screw up your mind reading it. What you need to do is keep track of fuel mileage from one tank to the next and than average out the mileage to see if there are any gains or losses from use.



I have tracked every gallon of fuel from the first day I bought the truck until now and my fuel mileage average has increased every year of ownership. I can tell you that when pulling a trailer the fuel mileage reading will be different every time you pull that trailer. The fuel mileage will be affected by wind, how fast you take off from a stop, how many traffic lights are on the road way, how heavy the trailer is for that day and other variables. That is why I average my fuel mileage and I do not concerned myself with hour to hour readings from a monitor.



Just food for thought.

Jim W.

 

[Bob4x4]

The exhaust brake on the 6. 7 engines turns the vanes in the turbocharger backwards. . spectrum to the other with the exhaust brake engaged. .





...

The vanes do not turn at any time,they are fixed it is a sliding mechanism







The Variable Geometry Turbocharger (VGT) uses a one piece sliding nozzle that moves continuously to vary the power of turbine and the amount of air delivered to the engine. This allows turbine power to be set to provide just enough energy to drive the compressor at the desired boost level in all engine operating modes.



Turbine power level changes are achieved by varying the position of the nozzle ring in relation to a set of guide vanes that control the flow through the turbine. An electrically controlled actuator positions the sliding nozzle over the guide vanes.

The VGT works in conjunction with the engine and the transmission to provide an integrated braking system used to help slow the vehicle. This is commonly called exhaust braking. This braking power is achieved by modulating the turbo sliding nozzle ring to restrict the flow of exhaust gases from the engine, which in turn creates a high back pressure on the engine. The high back pressure creates a high level of resistance to the motion of the pistons within the engine and this resistance is used to reduce engine speed and thus vehicle speed.



The exhaust brake feature will only function when the driver turns the exhaust brake switch to the on position. Once the switch is in the on position and the vehicle is moving faster than 8 k/h (5 MPH); the exhaust brake will automatically operate when the driver removes pressure from the throttle pedal allowing the engine to see 0% throttle and 0 fuel delivery.



Exhaust braking is most effective when the engine RPM is higher. The automatic transmission has been programmed to downshift more aggressively when the exhaust brake is enabled to increase brake performance. Use of automatic transmission Tow/Haul Mode improves interaction between the engine and transmission. Inputs to the exhaust brake feature include

 

[Bob4x4]

A slight dip in fuel economy would make sense since the truck will not travel as far with 0 (idle fueling) over a given time

 

[rwitt]

Bob 4x4,
I thought the ebrake only operated when the torque converter was locked while moving. Mine will work until about 20mph, and at that point the torque converter unlocks and no exhaust brake below that. It does work at an idle when the engine is cold for warmup. I see the OP has a manual transmission, is that what you are refering to when you say it operates above 5mph?
Rich

 

[Bob4x4]

The factory very rarely gives absolutes,so above 5mph is just a minimum. The lowest I have seen is 15mph

 

[Newt]

In my experience, the exhaust brake is RPM governed, not speed. Watch it and manually hold it in different gears. My exhaust brake quits around 1,000 RPM.

Newt

 

[rwitt]

In my experience, the exhaust brake is RPM governed, not speed. Watch it and manually hold it in different gears. My exhaust brake quits around 1,000 RPM.





Newt

Yes that is correct. On my truck with 3. 73's, thats right at 20mph.

 

[n7ki]

My truck is not an automatic, it is stick. When the exhaust brake is off and I am moving at 60 mph and I let off of the gas pedal, the mpg shoots up and the fuel flow decreases to . 6 gph which is same as idle conditions. When the exhaust brake is on and I let of the gas pedal, the mpg increases but not as much as with the exhaust brake off and the mileage goes to 6 mpg on the bully dog gauge. All I believe is that the two conditions, exhaust brake on and off, should behave the same with your foot off the gas pedal.
Up until now I have always used the exhaust brake. I have almost worn the paint of the switch for the exhaust brake.

 

[jhenderson]

Let's all remember something here. This is not a mechanical fuel flow meter. It is only an electronic estimate based on known parameters. Without a pitot in the fuel delivery stream, measuring actual flow, it's all just a best guess.