Small throttle positon for FE

[usergone]

The title may seem like a "been there, done that" thread, but hear (read) me out.

Just about any list of FE-improving driving techniques will tell you to keep your foot out of it as much as possible. More throttle = more power out = more fuel in.

To avoid confusion, let me mention right now that I have a diesel.

On my truck, I don't have a throttle pedal. I have a governor pedal. The injector pump compares the "target" engine speed (throttle position) to the actual engine speed, and injects more fuel if it needs to go faster and less fuel if it needs to go slower. This is nice because any time I am engine braking (above about 1000 rpm) it is in DFCO "mode." But that is beside the point.

The way that my injector pump is set up, there are multiple adjustments to the amount of fuel put in, but the most important one (for this thread) is the rack travel limiter. That is basically a full throttle stop for the fueling.

If I adjust that, it will limit me to a certain (consistent) small throttle position, and it is also impervious to the urge to floor it (because to "floor" it, I would have to take the cover off the IP again)

I have adjusted it to the minimum "throttle" travel possible, and the truck feels like it has about 1/3 the power of stock tuning. I will be filling up in the next few days and getting a feel for how the FE will respond. I suppose that, self control and overall interest permitting, I could even do some tanks ABA.

I am putting this in the "ecomodding central" subforum because it is a "mod" not a driving technique so much.

[brucepick]

I'm curious to see the results.

My guess is that you'll have a nice increase in FE but a reduction in available power. This probably won't be an issue as long as you don't have a steep upgrade or a very heavy load - in which case you'll need most of the available power of the engine's stock configuration.

In any case - in my humble opinion of course - North American market vehicles are sold with a good bit more power than they need, so you'll likely do just fine if this does indeed reduce your available power.

[usergone]

Originally Posted by brucepick

I'm curious to see the results.

My guess is that you'll have a nice increase in FE but a reduction in available power. This probably won't be an issue as long as you don't have a steep upgrade or a very heavy load - in which case you'll need most of the available power of the engine's stock configuration.

It actually reminds me of my jeep as far as power:weight goes... funny that

But, yes, I am wondering about the power decrease. I haven't driven it on a trip long enough to form an opinion yet, though.

[brucepick]

Originally Posted by thecheese429

It actually reminds me of my jeep as far as power:weight goes... funny that...

Just keep choking back on the IP till it reminds you of an early '60's VW beetle and you'll get truly superlative FE!

[MGB=MPG]

Rather than accelerate it will *Gather Speed*
one hopes you do not have the requirement to Merge in the Metroplex during the rush..

[bestclimb]

You could add a heavy spring to the linkage, short enough that for most of the time it feels like a stop then if you need the power you can overcome the spring force and get out of the way.

[usergone]

The adjustment actually does nothing to the linkage itself. It simply goes straight to the source and limits the fuel.

Actually, limiting the pedal travel wouldn't do much because if the target speed is far below the "stop point" it will still give full fuel. It is like a lawn mower governor the way my engine controls fueling. It is "speed governed" not "load governed" (a gasoline engine is load governed, that is why a pedal position could be fine in gear but redline out of gear; with my truck, if I am loading down the engine and take it out of gear, it will go to a certain rpm and stick there)

[usergone]

I put about 150 miles on this tank after the adjustment, and have just filled today to see a purely "small throttle" tank.

I did a lot of city driving. Mostly, in fact. I also learned a bit as well. The engine stays true to its commercial engine roots, shown by its flat power "curve." It will accelerate at the same rate from about 1300 to 2900 RPM. Also, a 6B (not 6BT for turbo) is not such a weak engine. Compare it to a geo metro and it still has tons more power.

However, this tank only came up to 19.5 MPG, and the last fill was topped off a bit higher than usual (which would make this tank look better). I imagine that the fuel limiting adjustment has the most effect while accelerating (or, rather, the only time it has any affect at all) because that is when I am trying to use more fuel. Even on the highway I don't need the full fuel to maintain speed.

I suspect that the fuel limiting adjustment will have little effect on the FE overall. However, I will run this tank without adjusting it back, just for the sake of scientific-ness.

I forsee a greater gain from a hotter thermostat and advanced injection timing.

[jakobnev]

According to all the BSFC-charts i have seen diesels tend to be most efficient when run pedal to the metal, so you shouldn't see improvements with what you are doing.

It would be interesting to see what happens to you mileage if you ajust your engine back, always accelerate full "throttle" and instead shift erlier(if that's what you need to stay at the range where you get best torque). And those times when you need to limit acceleration even more(some slowtard in you way for example) you still use full throttle and just shift erlier.

[usergone]

Originally Posted by jakobnev

According to all the BSFC-charts i have seen diesels tend to be most efficient when run pedal to the metal, so you shouldn't see improvements with what you are doing.

I am happy to say that it seems as though you are correct. I filled up yesterday: 17 MPG. Ouch.

Fortunately, now I get to put it back to the normal power level.