What are the conditions that result in a turbo diesel engine having reduced power? Specifically, an engine that runs strong consistently and then has an "off day" so to speak. Temporary (I hope) sluggishnes that it out of character.

Truck has 21600 miles, new fuel filters at 15K, air filter gauge is good. No fuel additives, Shell ULSD fuel today, I'm pretty sure that we don't get winter blend down here (SC,GA,AL). Turbo PSI was normal, max of just under 20 at high engine speed, 10 psi in normal cruising.

I drove just under 500 miles today, my GCW at the moment is 16K, verified by getting weighed. 4160/5100 and 6840 on the trailer axles.

Trailer is 16ft long, standard height, probably around 9 ft. tall from ground to top.

While driving my engine seemed slow and lacking which is something I never thought I would experience with this 6.7. Acceleration was off quite a bit. I could not merge onto the interstate at speed, approaching ATL on I-85 S and then down through AL to Montgomery the hills are pretty gentle. The average uphill slope would result in the transmission having to shift down to 4th gear to hold speed between 65 and 70.

I ended up spending all day in Manual mode to keep the trans. in 6th gear. Uphill climbs would result in a 5-10 mph loss, I would put it in 5th if I got below 65 and it would not gain speed, just hold steady. When on 2 lane highways I kept it in 5th. 6th gear was just not an option, my foot was at 100% throttle too often.

I burned 2 tanks of fuel with no change. Outside temps stayed 38-45. No rain, pretty dry air. Breezy winds but they were crossing, I drove mostly S/SW and the winds are NW today.

I am not complaining that I need more power, this thing is incredible. I am a little confused by today's drive though. It sure seemed out of character and I don't know why or if it will go away.

I know that in the cooler months gasoline engines actually run better on the cool dry air, do diesels run worse?

 

Trailer brake hanging?

 

Good question. The rims on the trailer were cool to touch at each stop I made. I may grease them tomorrow anyway. I will check the brakes tomorrow.

 

When I try troubleshooting something like this, I usually look at what I changed recently. Sometimes the obvious gets overlook (like fuel quality -- you mentioned adding fuel).

I fly small planes and they are very consistent but are subject to environmental conditions (heat, cold). They are also very rudimentary in design. My plane has basic fuel injection and a dual magneto setup. Flying this plane for 20 years, I have gotten to know all of her "variables" and can tell if something is out of whack. I would think state of the art trucks would be able to compensate for variations in environmental conditions. This leaves it to the other variables like fuel, brakes hanging, etc.

 

I experienced the same thing going to the Black Hills south of Deadwood, SD in Sept. (post flash). Wife and I were going to the same campground we had been to several time this year to go four wheeling for our 31st anniversary. The hill is about 7 per cent. Had both atv's in the garage. H2O tank was half full. Everything the same as three times b4. The truck would not go over 45 mph, would not downshift. I had to go to manual to increase speed. Cuz 45 just wasn't fast enuf, rite?

Seems to me I might have lost a little sumpn with the first flash in early Sept.

I have pulled the same 5er (pre-flash) up the Big Horn Mtns. on a 9 per cent grade 55 mph more than once. It comes off the mountain between 42 and 48 mph. Perfect! I love the way my truck handles that 18k toy hauler.

 

My best guess would be something related to fuel.

First thought was clogged fuel filters, but these trucks have a pressure sensor on the low-pressure fuel system that's supposed to detect a pressure drop that would cause performance issues.

I'm thinking maybe you got some low-grade fuel. I know lower cetane fuel can cause sluggish running and more soot, has it gone into regen more frequently?

I'd recommend dumping some grey-bottle Power Service in to confirm.

 

How about altitude?
They say this turbo setup does not like thinner air, and performs poorly the higher you go. My new truck is a pig compared to my '06. It almost feels like the brakes are always on.
I live at 7000 feet and work is at 9000'. Passes are about 11000'.
I am going to drive my F450 to the Midwest for the Holidays, so we'll see what happens at low altitudes.
Mileage with our Winter fuels here has now dipped to 15 (after a high average of 17.7). One dealer blames the AFE air intake, but it has been a slug since day one. Six thousand miles on the clock.

 

I have the AFE air intake, no problems......my travel trailer is around 10.5 - 11K loaded.

 

I have driven that same stretch of road several times, not an altitude thing there. I would like to know about the truck brakes, any added heat there? Maybe a sticking EGR valve? Could that have anything to do with this?

 

I will drive from Mobile, AL north to Tupelo, MS tomorrow and see how it goes. My commute today down here in Foley, AL was only 15 miles and I think the engine felt right, normal, and would scrub the tires in 2nd gear if I wanted to (with trailer in tow) so I am looking forward to tomorrow's drive.

Could have been a number of things ranging from EGR valve to weak fuel or brake friction. I can say that the motor definitely is louder than it was when it was new and I can actually hear things now, like the EGR cycle. Could be cooler temps too, I don't know.

Also, it did a regen cycle today, first time in a few thousand miles. That could have been it too. I run so much interstate with trailers that it hardly ever regen's. I can't even remember the last one.

 

I wonder if it could be "hill assist" malfunctioning, and applying too much brake at the wrong time?

 

Good point overkill, I am skeptical of the automatic trailer sway control too. I don't like the idea of the brakes being applied without my knowledge of it.

I do know that when the traction control activates the light blinks at the 8 o'clock position on the tach dial, I wonder if trailer sway has a light that flashes to let you know that it is interfering with your vehicle.

 

keep us posted ruschejj as i'm definitely following this one. I know you drive a-lot and will probably uncover stuff faster that most. Hopefully it will turn out to be nothing.

 

Here is what I found. This leads me to believe it's a message in the information center (if it gets bad enough) and/or the stability control light on the tach dash which I think is the same light the TCS uses.

 

Well, like I had hoped, the sluggish character I had is gone. I am back to easing into the throttle and watching the speed climb, the great feel of that power, your mind expects the motor to downshift but it never happens, you just roll your foot down and the speed keeps building and the smile is back.

I suppose it had to be fuel, could have been the DPF building pressure but not enough to get a cleanout cycle.

Thanks for all the help and support.