Over the past 2 weeks, I have seen several 2008s come in with reports of very poor fuel economy, here's what I have learned...
It is important to understand the operating characteristics when your DPF is regenerating.

High idle, around 1200 rpm in park or neutral, which will drop and start to "roll" slightly when the brake is depressed.
Some smoke and exhaust smell.
Slight lack of power and hesitation.
Intake sounds that are almost like the notorious 6.0 turbo fart.
Loud cooling fan noise.

Now, a regeneration can take anywhere between 10 and 40 minutes to complete, and it's normal to acheive an average of 5-6 mpg during regeneration. At higher city speeds and highway speeds, regeneration will not usually take much more than 10 minutes complete if at a steady cruise.
What I have noticed is the units with exceptionally poor fuel mileage have all been used in stop and go city traffic. In this case, if the DPF starts to regenerate, everytime you depress the brake pedal, the regeneration stops, untill the conditions are right, and will start up again. If this is the way you mainly operate, and all the conditions of regeneration listed above are present, it may be a good idea to let the vehicle idle until the rpm drops back to normal as to finish the regeneration without interruption to speed the process and let your mileage and such get back to normal.
As for what normal is, the reports that I have recieved show a 14-15 mpg average.

 

Great post! Thanks for the information.

 

Good info, let me ask as I have been doing a little checking into the poor mileage on these 6.4's and from what I understand about what I have read and been told how the DPF system works, seems to me that its a sure bet its going to affect the mileage somewhat.

With that all said, would it not be to everyone's advantage to use the fuel additives like the gray bottle Power Service to your fuel with each fill of fuel??? It sure sounds to me to be a good idea that might just indeed help keep the particulate filter media cleaner longer between the regen. cycles and that alone would help the fuel mileage I would think. Someone smarter than I and maybe someone with access to or has one of the 6.4's needs to let the rest know far sure about this possibility, as well as the rest like me that just likes to know stuff like this

Might need to add that if anyone was going to try the Gray Bottle Power Service, just make sure to get the new stuff approved for use with the ULSD... Its got that marked on the new stuff. I bought a gallon bottle of the older stuff just this past week because of the price$$$ of it, doesn't matter in my truck so much, it did get my truck to show off a hint more of black smoke when I hit the throttle a little harder for a hill or to go around someone. Don't think that would be so good for the 6.4 and its new DPF...

 

Thanks for the great post CanadaGuy, I think from what I 've read about the regeneration process with these new diesels, I think it'll affect all the big three diesels mpg, better get used to it until technology improves these new diesels, as for now I'll just keep my tried and true 7.3L diesel.

 

Now I wonder if the engine needs that much time to regenerate and when you hit the brakes it doenst count then it seems that someone that is doing alot of plowing of snow in the winter will have the worst fuel mileage possible.

 

I'm sure that plowing snow doesn't really yield the best possible fuel mileage anyway. Keep in mind, that regeneration might only happen once every 600 miles or more. From what I have learned about the system, you must use CJ-4 oil (due to it's low ash content), ULSD (with no bio at all is recommended), and if you're using an additive, it has to be a sulphur free additive approved for use in ULSD vehicles. That should keep the regen cycles down to a minimum.

 

Hey guys I read somewhere and please correct me if I am wrong but the regen mode is not supposed to happen all that much, maybe the first couple thousand miles its programed to regen but I thought once it is past the initial phase its only supposed to regen about every 3,000 to 5,000 miles or maye even more miles but I didnt think that its suposed to regen as often as you guys seem to be talking about. Oh well its something we all have to get used to with these new Diesel emissions rules.

 

Our truck regens very 150-200 miles (stock) with normal driving. Fuel economy has been around 12-12.5 mpg so far (3000+ miles).

 

Not for awhile has a truer statement been made.......

Ditto on hanging onto the 7.3L.........

Diesels are getting way too complicated and the fuel mileage is starting to really suck......

Let me ask y'all here........If we're adding all of this high-tech, low-emissions technology to the diesel engines to keep the air cleaner (jury's out on that one), but in the process, the engines start sucking down diesel like a champion guzzler in a beer-chugging contest, what in the hell is the point?........

 

well i guess its either sucking down diesel or replaceing a $1,000 Particulate filter every 150 to 200 miles. Im for sticking with my 7.3L also until I win the lottery.

 

You don't replace the PF every 150 to 200 miles. An automatic cycle is run to inject fuel into the exhaust to burn off the PM (particulate matter) in the trap.

 

Here's a tad of info...
ISSUE:
2008 F-Series vehicles equipped with the 6.4L diesel engine are equipped with an oxidation catalytic converter (OC) and diesel particulate filter (DPF). The function and operation of these parts may cause some customers to perceive an issue with their vehicle.

ACTION:
Review the Operating Characteristics with the customer.

OPERATING CHARACTERISTICS

Diesel particulates in the exhaust are trapped by the DPF. Regeneration is the process by which exhaust temperatures are increased so the particulates are combusted.

The frequency and length of regeneration will fluctuate as both are determined by the drive cycle. For most drive conditions, regeneration frequency will vary from 100 - 600 miles (161 - 804 Km) between occurrence and last from 10 to 40 minutes. The first regeneration does not require 100 miles (161 Km) and may occur at any time. The length of regeneration is usually reduced if a constant speed above 30 MPH (48 Km/h) is maintained.

The following is a list of normal operation while the vehicle is in regeneration, and do not require repair. If you are not sure if the vehicle is in regeneration, IDS can be used to monitor the Diesel Particulate Filter (DPF) PID.

Engine idle speed can be 1100 to 1200 RPM in park/neutral with foot off brake.
High idle speed drops to within 50 RPM of normal idle when the brake pedal is touched, PRNDL is actuated, or clutch is actuated.
White smoke in cold ambients is normal and the amount will be increased during regeneration.
Powertrain power is limited to 325 horsepower (HP).
Engine responsiveness may be slightly different than normal operation.
During initiation of regeneration, exhaust smell may be noticed - especially on new vehicles.
Powertrain sound will be different including air induction noise (including flutter on deceleration or engine shut down), exhaust noise, and changes in engine radiated noise.
During regeneration, exhaust temperatures are elevated.
The following is also normal and may be observed by a technician using a diagnostic tool. It is not likely that a customer would be aware of these:

The throttle body is only active during the regeneration process and during shutdown.
EGR is not operating during regeneration.

 

I own a 5.4 gas but have been following the new 6.4 carefully and I have to say Im a little confused.The new emissions seem to be a joke,the mpgs have dropped 5-10 from the 7.3 and this is environmentally friendly?Sure the 6.4 may put out less emissions but when you factor how much more fuel it uses in a year with the pollution the refinery produced to make the extra fuel used I doubt it is any less than the 7.3.Imagine that, our fearless leadership has found an "environmentally " friendly solution that makes you use more diesel fuel and prices are again going up.

 

When will there be a Diesel Oxidation Catalyst and DPF delete pipes available along with a programmer to get rid of the REGEN Cycle LOL! Sounds to me like the 6.4 shoulda came along before the implementation of the DPF and we would have some powerful trucks.......

 

yuck... Maybe I should buy a 2nd '07 just to hold onto as an investment .... I'm just picturing someone with a 6.4 towing heavy up a hill and trying to pass a slower vehicle when the truck decides to do a regen. That would suck big time...