This past weekend I made my first long (for me) tow with my 6.7. I have a 20x8 cargo trailer that I take to enduros, so it's loaded with a couple dirt bikes and a bunch of gear. My guess is that it weighs around 5-6k loaded. I realize that this is well below the truck's capability. So I took it for a 600 mile round trip run this past weekend from the jersey shore up to northern pa. Truck handled it great, once on the highway used the manual trans mode and it pulled the trailer fine, egts got up to maybe 800 on some of the climbs and averaged about 12-13mpgs. I was very happy with all that.

I have an Edge Insight CTS and was watching the EGTs and soot count the whole trip. The EGts were high enough to keep the soot count low (around 1.9-2.2) the whole trip, with the exception of when we were stuck in some traffic and the the soot count ran up to about 2.5. Right after that bit of traffic and the soot count reached 2.5, the truck kicked off an active regen. Typically, an active regen would not start in my truck until the soot reached 2.7, so was interesting to see that happen.

Any thoughts?

 

yep i;ve noticed that while towing my soot will drop without going in to active regen.

this weekend i pulled the trailer (10K lbs) for about 30 miles. when i hooked up to the camper the soot was up above 2. when i got off the interstate after pulling the camper (25 miles on the interstate at 65mph) the soot had dropped to 1.4. When the EGT's get up (working the truck) I guess thats what they call a passive regen. Next week i am pulling the camper to Tennessee (about 400 miles each way). so it will be interesting to see how she handles the bigger hills and what the soot and EGT's do on a longer pull.

i betting i wont have an active regen the whole trip.

 

My truck kicks off an active regen any where between 1.7 and 2.5. I have no idea what the reasons are for when it triggers the regen. I just don't worry about it any longer. The trucks computers read some parameters and make the decision.

The exhaust system does a passive regen any time your EGTs are above 572° So you can see a reduction in Soot% during any drive where you sustain those higher temps. But the trade off depends on how much new soot you are creating. anytime you are running on the rich side of the fuel flow, You will be creating more soot than the passive regen can clean. (i.e. climbing grades with a load and the boost is high) When you are running on the lean side of the fuel, ( i.e. a level grade towing with very low boost) The passive regen will keep up or actually reduce the soot %

I've driven multiple trips towing large trailers and not seen a regen for the entire 900 miles. Other trips with grades where I've got my foot in it, the turbo maxed out climbing and I'll see a Active regen in 50-70 miles

Think of the trucks you see on the road that blow black smoke when they pull away from a stop sign or punch it when going up a grade. That black smoke is the soot that the DPF is now catching in our generation of trucks. Those same trucks that blew a big black cloud as the got moving, Blow almost no smoke once they are up to speed and the fuel leans out. This same process is happening in our engines, But the DPF is catching any of the smoke so nobody sees it.

 

PH, you bring up a point I've been meaning to ask about...

while I like to get into the taller gears when towing and let the torque @ 1600 rpms do the work with less drama of upshifts, downshifts, etc...

are we doing worse by not letting the rpms get up a bit ? i mean with mpg, soot, etc... ?

just wondering as the truck will do what I need to do in a wide range of conditions...

 

I don't have the insight but I can confirm what y'all are stating. I tow all the time going long distances and my truck will regularly travel more than 700 miles without an active regen.

One of the handful of reasons I left my 6.4 at the dealer two years ago. I liked my '08 but this 6.7 has reduced my fuel consumption dramatically with the greater efficiency. The passive regen has a lot to do with that.

Mr Adams, I know what you mean. Lugging the motor, using 100% throttle to climb a hill in 6th at 1600 rpms is really nice (not really lugging but pouring fuel at low rpms). That's a tough nut to crack. I feel that the 6.7 is a mid to high revving motor and likes 2200 rpm.

So, full throttle at 1600 rpm or 40% throttle at 2200 rpm? Which is better? If I had an insight I would probably choose the one that kept soot count lowest.

 

I'm thinking that you guys are reminiscing back to the days of mechanically controlled diesel engines. Back then you could cause harm to the engine by applying full throttle at lower RPMs because the pump would deliver more fuel than could be burned. In fact the owner's manual for the Dodge/Cummins trucks of the era stated that this was abuse and damage would not be covered under warranty.

Electronically controlled diesels do not suffer from this problem; not even a little bit. You can apply full power at ANY RPM and not have a problem because the PCM has very precise control over the fuel injection and will never overfuel unless something is wrong. Remember that if programmed wrong your fuel system has the capacity to overfuel at any RPM, as it's capable of pumping much more fuel than is actually required. But it doesn't, and this is because of your sophisticated PCM. When I was in truck driving school we were taught to keep engine RPMs at the absolute lowest possible to keep the truck doing what it should, and the Caterpillar C15s that I drove the most loved WOT at 1,200 RPMs. Peak horsepower came at 1,900 RPMs, and Caterpillar's recommended specs were 65 MPH @ 1,250 RPMs if I remember right.

Shake the old myths and drive your truck. You wont' hurt it.

 

i agree...with the pcm controling things we are not likely to hurt the truck unless tuned and modded.

but (even stock) if the engine is lugged it causes less boost and you have to go WOT to maintain speed so you are dumping more fuel in. which if we didnt have the DPF would blow more black smoke. So the DPF is collecting more under this driving style and therefore potentially hurting fuel mileage from a clogged filter and having to do more regens.

does that sound right? or is my logic off?

I have noticed watching EGT1 that the temps go up with more lugging (lower rpm) and less air flow (boost).

 

It's a bit off in my opinion. You are dumping in more fuel up to the point where there is not enough air to burn the fuel; the PCM will not exceed this point on a properly functioning truck. Tune it and all bets are off of course, but the PCM knows exactly how much fuel can be burned.

Take any properly functioning pre-DPF electronically controlled diesel engine and lug it at WOT all the way down to idle and you should see no smoke.

 

The ECM will actively regen at a minimum mileage interval regardless if it is needed or not at that point in time. On my truck, that minimum is around 600 miles.

 

That's exactly what I noticed; the soot level was below when it would typically regen, but I do know that I traveled about that far since the last regen....thank you.

 

I did not know this.

I had mine start an AR at 2.26 one time during a tank of B10 but it always starts at 2.66 or above 99% of the time after EOT is at least 150F.

 

Exactly. Watch your EGTs as you climb a long steady grade. You may stay in high gear, but the boost and the EGT's climb. Down shift a gear and move more air through the engine and your EGTs will drop 200° with in 15 seconds.

I have no idea which is more fuel efficient, lugging up a grade at 1600 rpm in 6th or at the same speed but 2000 rpm in 5th gear. But the EGTS definitely are cooler at the higher rpm

 

Where were you riding?

 

Was riding the Barbed Wire Enduro in Gillette PA, a few miles south of Elmira, NY. It's one of the ECEA events that is hosted by the Southern Tier Enduro Riders club. It's always a great event and a lot of fun, one of the best runs of the series IMHO. You ride?