How do you eco-drive a diesel ?

[MazdaMatt]

F350 with a big box (not a pickup truck box, more of a moving truck box that I use to transport my track car instead of towing it on a trailer).

Typically under normal acceleration, it shifts around 3krpm and under normal on-throttle deceleration it will downshift around 2krpm (i think). It is REALLY frustrating to be sitting at 62km/h at 2900rpm (ish) and the damn thing isn't shifting. Redline is about 3200rpm.

[TestDrive]

You didn't indicate a year. But based on Ford F-Series (Wikipedia)
it's good guess that you've got a Ford C6 transmission - (Wikipedia)

I'd verify that, then discuss it with a good transmission mechanic to see if what you've got is shifting like it should. Kind of suspect it is, but I'm no expert. While you're talking it over with the mechanic, you might want to ask questions about conversion to a automatic/manual shift, valve body or a full manual shift, valve body. (As in would it be a plausible DIY project? - I don't believe the parts are all that expensive compared to the probable gains FE.)

Something came up. Gotta go now. May post more on this later.

[Duffman]

I was thinking of the full manual valvebody as well. He will have a C6.

Anything that you can do to free up the intake track will help as well, those things got some intake baffling junk you can remove. Lots of good info on the Ford truck forums.

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[MazdaMatt]

oops... last night i typed up a reply but i didn't click send. It is a 1994 with ~166,000 km (100,000 miles?)

The manual valve bodies are interesting. I hate driving auto, so that would be a nice change. They are about 300 bucks, but depending on how long i own the truck and how many trips to the race track i get to do next year (just bought a house) it may be worth it so i can short-shift it and live with slow acceleration... or drive 64km/h without it repeatedly up/down/up/down shifting.

I will check out those sites. Thanks a lot for that list of links. Also, i will have a look at the intake path. It has an exhaust you could stick a leg into.

[TestDrive]

Originally Posted by MazdaMatt

Typically under normal acceleration, it shifts around 3krpm and under normal on-throttle deceleration it will downshift around 2krpm (i think). It is REALLY frustrating to be sitting at 62km/h at 2900rpm (ish) and the damn thing isn't shifting. Redline is about 3200rpm.

The more I think about it, those shift rpms sound reasonable for a gasser, but entirely too near high end of scale for a diesel (more torque at lower rpms). I wonder if all oem C6's have the same valve body. Any chance some previous owner changed out the transmission? eg C6 tuned for diesel came out and was replaced with new/used/rebuilt C6 intended for gasoline engine? (Not even certain that's a valid question to ask.)

Before you talk to a/the transmission mechanic, crawl under and look for vacuum hose or electric wires leading to a shift modulator on the transmission. Could be a $20-$40 part may help the delayed shift problem.
If it's a vacuum modulator, check for a leaking vacuum diaphragm. If it's electric, look for frayed/broken wires. Consult manual for how to test.

While you're under there, write down the info off the tag on the rear-end. The transmission specialist might want to know what size tires & wheels - write that down too.

What does the transmission fluid look and smell like?

Any idea when or if the transmission fluid and filter were last changed?

Hope this helps.

[MazdaMatt]

The truck was previously owned by Hostess as a city delivery truck. Then purchased by a guy that used it to haul his off-road racer (he installed the ramp door). Hostess apparently had a rock-solid maintenance schedule and the second owner runs a small trucking company. I can ONLY ASSUME that the fluids are doing fine, but who knows if that tranny is correct or the valve body is correct... he may have scooped it up chneap from an off-road racing buddy. I woudl LOVE it if i could replace a 40 dollar part and have it start upshifting at 2000rpm instead of downshifting at that!

Great suggestions.

But moving backwards a little... what about driving technique? I follow trucks and i drive f'ing slow, i try to maintain speed at the lowest possible in the highest gear... i refuse to neutral coast because i did that once and it clunked HARD on every shift for the next hour of driving.

[Duffman]

The 7.3 should have a different bellhousing than the gas jobs, Ford was/is terrible in that regard.

[Duffman]

Matt instead of accelerating slow, maybe try to get through the first two gears briskly, then slow the acceleration.

[MazdaMatt]

...Actually... i do that... i don't floor it, i just try to "lead" the gas pedal. ie, if 3/8 gas would sit at 25, then when i'm doing 25 I have the gas down to 5/8... when it shifts, i drop back down to a little more than cruise throttle... i don't spend much time in each gear... which is easy because it is in top gear at 65km/h (40mph? guess?)

Funny enough, i think the best mileage trip i ever had, i spent about 3 hours in first gear at idle... it was stop/go traffic and i played the accordian by simply sitting there iwthout touching the pedals.

[instarx]

WARNING! Fluid dynamics post!

Originally Posted by ConnClark

If this is so then please explain the attached picture.

Once again I disagree. Any drop in pressure would be due to air flow restriction compounded by differences in velocity of the air flow at he points

I just woke up and will address many of your points later (you made some good ones, but mny are still incorrect) - but first, that picture.

That, that...thing , does not measure what you think it does. Note that the pressure appears to be LOWER in the area with high velocity air. But this is exactly the opposite of what you claim should happen when velocity pressure adds to static pressure, so how can that be? It is because the apparatus actually demonstrates the Bernoulli effect, where high-velocity air moving across an opening creates a localized low pressure area proportional to its velocity.

Those manometers are not measuring the static pressure along the tube, but the relative strengths of the three localized low pressure areas created by the Bernoulli effect. It is not possible to even estimate the static pressures along the tube with that poorly designed apparatus (who would ever connect three manometers in series like that - you can't tell which is measuring what). That contraption is a perfect example of how somone who doesn't understand the principles (not you, the people who put it together) can design an "experiment" or demonstration that they only think illustrates their point (unless the caption to that picture is "Demonstration of Bernoulli Efect" or "World's Worst Design of a Pressure Measuring Apparatus Using Manometers").

A general comment about your interpretations of the relationships between velocity and pressure: Be careful not to confuse cause and effect. Air movement (velocity) is caused by pressure differentials, but the inverse is not true - air pressure is not changed by a parcel of air simply being in motion. This is true in air systems ranging from continental-sized weather systems, to air being pulled through a duct, to the air moving around in your living room.