why not raise the idle speed?

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

a guy on ecomodder.com eeeked out a few more mpgs with his tires @ over 40psi. The safety, wear or handling characteristics were not discussed.

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Cheers,
Robert

something I was thinking on the way home too. what would happen if I set up a button to a vacuum changeover switch to block the alda line for the turbo enrichment on the highway? would this make it like a NA and maybe use less fuel since there doesnt seem to be much need for the extra power on 65 mph morning/afternoon commute?

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

You're a bit confused on the function of the ALDA. It's a fuel limiting device. At low rpm levels, where there is insufficient boost, the ALDA limits fuel so the engine does not smoke. If the driver mashes the pedal, the IP won't allow full fuel until the boost comes up.

You can remove the ALDA completely and get the same fuel economy as you currently get by being judicious with your right foot.

Think of this this way: The more you press the pedal..........the more fuel you get.

The turbo models are noted for slightly better economy than their n/a predecessors..........even though they have considerably more power available for use when needed. Naturally, if you used this power on a daily basis, your fuel economy would be significantly poorer than the n/a vehicles.

Will rev matching work? Just a thought.

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Actually not. They seem to need to select a lower gear and then instantly realize that an upshift is required. The transmission seems confused.

Throttle and RPM.

I do not believe a mechanical governor has the ability to shutoff the fuel from the simple inputs of throttle and speed.

I'd be interested to see where you found such info.

Here is how I understand it. When you let off of the “gas” the governor closes the rack and cuts off fuel to try to get the engine to reach idle speed. When you are engine braking the engine is being spun at higher than idle engine speed so the governor will keep the rack in the closed position. I am not sure if it is providing no fuel or idle fuel in this case, but in any case there should be no benefit to coasting.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

On that light I also noticed that if I am actively maintaining speed, and then I let off the pedal, at that moment when I let go of the pedal, the engine speed drops maybe 500rpm while the vehicle still maintains the speed, albeit decelerating. What causes that 500rpm drop?

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That's the question.

I'd really like to see how the governor can shut the fuel completely and then turn it back on just as the engine reaches idle. This is the purvey of electronic controls. I'd be positively astounded if they accomplished that task mechanically.

The mechanical tolerances in the pump, as the pump wears, would dictate continuous stalls on many different engines if such a system were implemented. The fact that it's nearly impossible for a 617 to stall when coming down from high rpm to idle on decel would most assuredly point to continuous idle fuel.

....but, I'm open to further data, if anybody has it.......

That's the torque converter slippage. It has transitioned from a higher engine speed that drives the wheels to a lower engine speed whereby the wheels drive the engine.

When both the impeller and the turbine are turning exactly the same speed, there is no torque passed to either device...........the engine doesn't drive the vehicle and the vehicle doesn't drive the engine.

Brian, now that you mentioned it, my 300D stalled once after a hard drive on the highway that came to a crawl. I had to brake hard, the engine sputtered and died as I was still coasting at slow speed, shifted to neutral and restarted. All was fine afterwards though...

Oh ok, so that 500rpm drop isn't the fuel cutoff mechanism that Bgkast mentioned?

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Yes, I had the W123 stall once myself. It doesn't signify a generic problem.

No, the 500 rpm drop will occur regardless of whether the fuel is at idle or whether it's completely shutoff.

I believe the governor is controlled by fly-weights so it should be possible for it to shut off fuel when the engine is providing braking at RPMs higher than idle, then begin to feed in fuel when the RPMs drop to near idle speed. I have a BOSCH manual for the governor at home that I will look at later.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine