New to me 2004 Cummins Ram

[Hersbird]

Well I finally got my first towing test of a little over 400 miles. I had a few problems. On the way over I got a sudden loss of power on the biggest hill and a check engine light. The code was P2121 which is a throttle position error. I was able to get it to come back to responsive and tried to clear the code but the check engine light stayed on and then cleared itself in about an hour. Then we stopped for 20 mins, and when pulling out we got a surge in power, then the dead pedal again and the light. The pedal was working like either 0%, then any application it shot to 20%, then any movement of the pedal higher did nothing, stuck at 20%. It went back to normal after about 5 mins but the light stayed for the rest of the trip. I ordered a new TPS that will be here tomorrow, but I also did a reset and TPS relearn while I was sitting 2 nights, and then today on the return trip I had no issues. The TPS was $275 and I wonder if I really need it or if it was a loose negative battery terminal (which didn't seem as tight as it could be during the reset procedure.)

Anyway as far as economy I got 10.73 MPG towing at about 65 most of the way on the day with the TPS acting up. The return trip (same route, maybe a little slower because of rain) I haven't refilled again yet but the gauge is a good 1/8 of the way higher so I'm hoping for better. The return trip is technically more uphill by about 1000 feet so that's a good sign. If it is that much more gas in there it will be more like 13.4 mpg so fingers crossed that TPS was messing with economy.

The way home I did have a different problem, a muffler clamp separated and opened the exhaust up. I was able to find a NAPA and got a little section of pipe and a couple of clamps and fixed it in a downpour in the parking lot but had to drive 50 miles trying to avoid 1650-1850 rpm in 6th where a deafening drone was present.

Overall not a good test, to many problems, to many variables. If it's only going to be 10.73 mpg I'm not happy, 13.4 would make me happy. The truck can certainly effortlessly pull the camper at least.

[slowmover]

As always, towing penalty should be about 40% where all else is the same. That last bit often overlooked: truck needs to weigh the same is one, and towing speed should be the same as solo. Use of cruise control makes for better comparison.

At this point in trucks life, getting repairs done plus all book maintenance to date is crucial.

At highway speeds with an aero penalty trailer, it takes very little to drop mpg like a stone where computer is confused.

Have you run a route of about 200-miles? Out and back? Think of it as the test track. From a truck stop with a Cat Scale. Apples to apples (not yet happening for you).

Trailer axle leaf suspension broken down and rebuilt? Axles aligned? Shock absorbers installed? Hitch weight verified? Etc.

So, past truck issues, both trailer and the lash up need to be gone over.

Just the WD setting with mine being off was worth over 2-mpg. At 55.

[Hersbird]

I didn't want to make this long run my first run but my dad is sick and my, and my brother's family made a run to visit and help him with some land cleanup before fire season. He has a very small house so the camper was needed. Overall a great trip even with a few problems.

[Hersbird]

I did notice that when pulling a hill, nothing major just an average uphill, that the EGT would get to say 1000-1100 in 6th but the boost would stay lower say 18 psi. If I shifted to 5th I would get lower EGT by 100-200 but more boost by 4-6psi. No change in speed, just the gear. So what's better for economy, lower EGT or lower boost?

Steady state, flat land 60 mph it runs about 675 EGT and 9 psi boost.

[gumby79]

Peek torque +- 50rpm( check for your motor / tune) should be your sweet spot BSFC below consumption rises fast. Hold peak as long as you can then down shift . What is the rpm difference from 6 to 5? I assume@60mph.
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Computer/ tuner may be the limiting factor keeping your motor from being able to hurt it self at or above 1,200°f with a 100°f buffer. Or if slower than peek to far there may not be enough gass flow to provide more boost.

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Is egt probe before or after turbo?......... there is an aproxamitly 250°f drop across the turbo...
----z
With my stock tuning 1000°@15psi ,cold side, is all I can do normally 1100 with enough speed and grill block, empty

[Hersbird]

The rpm at 60 is about 1800 in 6th and 2200 in 5th if I remember right. The EGT is just before the turbo. It will go much higher than 1100 and will boost up to 31-32 psi where the waste gate opens and puts it about 29 psi. The EGTs then go over 1400. I try to stay away from that kind of boost and temp instead letting it lose some speed and just slow down some on the really steep passes.

[Hersbird]

The return trip did worked out to be 12.4 mpg so better but still not great.

[darknightdiesel]

Hi,

New here but just make sure your running fuel supplement, your truck was designed to run on LSD fuel and only ULSD is available at the pump,

The ULSD fuel has too low a cetane rating and not enough lubrication, its not compatible,

[slowmover]

As always, addressed to anyone with an overpowered TD pickup:

6-6-6 Rule

60 mph
600F
6-psi

It doesn't mean much in practice. It's representative. Diesels like to be worked. Which is more important.

All one does is to establish habits which make for best conditions: avoidance of other traffic the priority. Safety, and economy follows. As an exemplary habit, back off to get other traffic around faster. Crowds or individuals. Thus, "managing" traffic means more than set speed rpm, MAP or EGT.

Turbodiesels are not gasoline motors. Throw out that thinking. Doesn't apply. High cylinder pressure is a different motor. Increases to vehicle weight and grade ascents don't affect them the same. Let it tell you what it wants. It will.

Drop from Overdrive to Direct as needed. Let the engine work. Percent engine load is more useful than EGT or MAP. Don't exceed 80%, as a rule. Experience will make smooth. Anticipation, how to shift (not when), how to maintain headway will come with practice.

Focused on mpg will not give results desired. You wouldn't hike that way. You'd have establish a good pace. Neither fatiguing nor apprehensive. The goal with both is to not arrive exhausted. Even tired.

It takes practice. Mindfulness you've already got. But apply it to the flow. Headway.

Fix the mechanical items. Measure those relationships (in spec). Then let it run as God and Clessie intended.

These days I'm running a smoothbore tanker. No internal baffles. 5000-gals in a 7000-gal tank. "Anticipation" is all I do. Can't stop, can't lane change and can't regain speed without an opposite (sometimes dangerous) reaction from that product sloshing around. To maintain headway I have to accept low mpg in some situations, as controlling the rig (and that liquid) is paramount. Take a page from this book: deal with traffic, terrain and weather for best outcome. Road & Load. Lane-centered and still upright. Let mpg take of itself. It will.

This rig sports a revving 12L Cummins. Not a big power 15L. I complete ten gear changes when loaded before I hit 15-mph. 250-rpm shifts. With another eight to go if I'll be running top speed. Try for some relative stasis with that fluid back there. Done badly it will literally stop me in my tracks. When to shift is "simple"enough (time according to slosh; wave periodicity and two waves at once make it interesting), but how to bring the engine back into engagement is another.

One has to have enough power at the re-engagement point to be smooth. This isn't different than with my personal rig. I'm not aimed at a particular FE rpm, but the one based on power. (The throttle exists only to move between gears).

One looks to the percentage change from loaded to empty. For this work rig it is from loaded to empty. At this stage it looks like 25% (early days). Remember that the addition or subtraction of 43,000-lbs is the only change. Your comparisons MUST be as exact to arrive at a solid baseline (once repairs and maintenance are complete).

The only thing that matters is the average (predictability), and the percentage change to that average on an annualized basis in order to decipher fuel economy. Work done well first, and cents-per-mile second.

[slowmover]

See the 2011 discussion: What is Engine Load Percentage (Ultragauge Question).

My long winded bit above is more icing than cake. Trying for context. Throttle is always going to be moved or dropped, long periods of no throttle in anticipation of downshifting, etc. How to be smooth in transitory states, I should have stated, is the meat on the bone. Not exceeding 80% of maximum means a limit on throttle movement to change from one state to another.

Driver has to be well out ahead of the truck (as pilots say of aircraft). Throttle changes may no hurt as much as with a gasser, but extended periods aren't warranted either. I'd rather drop gears, and then transition back up.

In a loaded pickup towing a fair sized trailer, this may mean slowing more than one expects. To drop a gear. And then another.

The rule for hill climbing is to drop low enough in gearing to be able to accelerate up the grade. That's usually the gear with which to descend.

Alternately, in accelerating onto a highway I don't wind the truck out till Fourth. Redline in Fourth and Direct really works. Makes up for being slow in lower gears as one can now maintain boost between gears. (Assumes a busy highway). Don't slide into Overdrive too soon. And get out of it (towing; heavy) early. Thus the bit about long periods of waiting. Feels long. (That how to shift business). With "80%" as an upper Engine Load limit, tailor other matters to suit.

Experiment.

I've run the big truck 6000-miles now. Learned to control that fluid slosh. What cruise control speed is best based on usual parameters. Same geographical region and temps. Overall average is from 5.8 to 6.5. Or, 12%. (That would have you to near 14-mpg).

"Feel" is crucial. Big picture versus details of gauge readings.