I've been reading of Lance's ALDA trials and tribulations (ALDA 1 & ALDA 2 and got to thinking (dangerous, I know) about the ALDA, it's function and how OM617.952 off-idle performance might be improved.

If I understand it's functon correctly, the ALDA limits the amount of fueling that occurs at high IP power settings (ie WOT) when a low-boost condition exists. Adjusting the ALDA screw CCW incrementally increases this initial fueling at low/no boost and, as boost increases up to a certain point, so does the ALDA fueling due to expansion of the aneroid capsule in the ALDA. I'm assuming, that at higher power settings some other mechanisim in the IP takes over from the ALDA for fueling.

In Lance's case, he ran experimentally without the ALDA and noticed an improvement in off-idle performance. This leads me to believe that some sort of mechanism or device that provided a false boost signal to the ALDA while the turbo spooled-up might just be a solution to off-idle sluggishness. Granted, using it in that fashion would cause smoke but, the device could easily be demand invoked so that you would have extra pickup 'just in case.'

A regulated, switched ~10psi compressed air source, plumbed into the ALDA line between the banjo fitting and the overboost valve would probably do the job without risking damage to the ALDA's aneroid capsule. Some sort of backflow preventer would be necessary to prevent the pressurized air from escaping into the intake manifold.

Very little air volume would be necessary so a belt driven air pump from an 80's era gasser or, a 12VDC compressor plumbed to a small pressure cylinder could provide the necessary pressure signal.

Ideas? Comments?

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Never a dull moment at Berry Hill Farm.

Most of my knowledge comes from discussions with Dave regarding the ALDA on the 603.

The general idea of the ALDA is to provide fuel to the cylinders based upon manifold pressure. With zero (gauge) manifold pressure, the engine needs X amount of fuel. With a manifold pressure of 10 psig, the engine can utilize 1.68X amount of fuel. If the ALDA is calibrated properly to the engine, with zero gauge pressure, the fuel provided to the engine will be exactly proportional to the available air and will be fully burned.

As the pressure rises, the ALDA gets the signal from the manifold and further opens the rack depending upon it's calibration. There is a maximum limit to the range of the ALDA. Somewhere around 12 or 13 psi.......it's not exactly known.......the ALDA runs out of available travel and won't increase the fuel no matter how much boost is provided to the engine. I've wanted to remove the ALDA and put a calibrated pressure supply to the ALDA and see exactly where the ALDA runs out of travel. Brandon was preparing to do this until he decided that he no longer wishes to associate with us.

Overriding the ALDA is the maximum fuel quantity in the IP. Even if the ALDA had unlimited range, it can't provide more fuel that the maximum fuel quantity setting.

The ALDA has the capability of shifting the response curve to the left or the right with the screw on the top. If you turn it CCW, the rack immediately provides more fuel to the engine...........without any boost........right off idle. Naturally, this additional fuel means that the ALDA will now run out of range at a lower value at the top end. If the ALDA had a range up to 13" before you adjusted it........it will run out of range at somewhere around 11" (a WAG) after you adjust it. The travel, AFAIK, is fixed.

I'd sure like to remove one and test it under various settings of the adjustment screw and see......precisely.......when it runs out of range.

As far as sending 10 psi to the ALDA when off-idle........this would probably be similar to hitting an ant with a sledgehammer. The adjusting screw of a properly functioning ALDA currently has enough capability to provide too much fuel off idle with an accompanying smoke condition. Therefore, no further modifications should be necessary. The key to this discussion is properly functioning ALDA. If the seals are leaking badly, the travel of the unit will be severly limited and all judgments based upon the performance of the vehicle will be incorrect.

Good explanation Brian! Thanks!

My single largest complaint is the inability of the engine to quickly pick up RPM (what I call off-idle response) when the car is loaded (in my case with the wagon, pulling a trailer) or starting out on an incline (remember, my wagon is a manual).

It seems like temporarily shifting the ALDA response by providing it with a false pressure signal (maybe 10psi would be too much but a pressure-regulated supply could address that) would solve the slow reponse issue at the expense of some occasional smoke production.

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Never a dull moment at Berry Hill Farm.

I sense that your expectations might be greater than the capability of the engine. When perfectly setup, these vehicles have a "decent" feel off idle and will accelerate with traffic without the requirement to floor the pedal.

However, you add the situation of a vehicle with a load (a trailer) and an incline, simultaneously, and all bets are off. Even with an overfueled condition, the engine simply does not make a lot of power below 2000 rpm. It's airflow is relatively low and it's rpm's are low and no amount of fuel will change this.

The ALDA will provide all the incremental change that you could require. If it's properly functioning, turning the screw fully CCW will be more fuel than you can use. Additional fuel will simply produce more smoke.

Now, if you could get more air into the cylinders below 2000 rpm........with a smaller turbo for example........now you'd have some more capability.

Breathing is the key.
maybe removing the muffler and going to straight pipe?

DAnny

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To test the travel of the ALDA unit we could attach the end of
dial indicator into the unit on a bench.
apply pressure with a bicycle pump and measure travel.

I have an off the car ALDA at home and can probably rig up
the dial indicator. That will solve the maximum travel issue.

I agree with Brian that by using the screw you then change the max boost
limit because travel is finite.

But the principal proposed by R Leo is correct, applying compressed air
to the ALDA at idle would simulate boost and supply more fuel.
Sort of trick the unit into thinking there is boost.
The upside of this is the ALDA would still enjoy full travel and not lessen
the upper limit. IMHO.
Sort of the best of both worlds maybe ?

Now - what happens when we install the shims ? I used a .045 (or so)
shim to give me more low end fuel (I think), while maintaining the full
travel so I would get fuel at boost also. Instead of giving up CCW turns of the screw to gain low end, I used the shim.
It was the middle of three sizes I had. (.020, .045, .062 or so).

A little off topic of ALDA, but I read the thread about pumping propane into the air intake
and just get giddy thinking about the idea of adding fuel straight into the
cylinders.
Kind of like when we discovered nitrous almost 30 years ago.
I saw my first nitrous rig on a camper while working as a gas station attendant in the 70's. Nitrous is not just for streetracers.
And propane added to boost could add some serious power.

Back to ALDA - what would the advantage be to some sort of a fuel control
that pushed or pulled the connecting rod (the pin that the ALDA lets rise
as pressure increases). Sort of an improved ALDA replacement that
a driver could dial in on the fly using either comressed air or mechanical
means. Sort of do away with the aneroid capsules.
What would we gain ?

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80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250

Don't some trucks use direct drive blowers ?
You want increased air, use a blower.

But really, Brian is right about the expectaion of power.
Face it - 5 cylinders, 3 litres. Lots of Torque.

You want horsepower, we used to always say cubic inches.
Sorry to disappoint, but you gotta have the right tool for the right job.
When I want dependable, economical, low cost to maintain - I drive Diesel Benz.

When I want throttle response and horsepower I drive big cubic inch gas engine.

__________________
80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250

Actually, the lack of torque is the problem. Torque moves the vehicle. Torque at higher rpm's provides horsepower.

The 617 doesn't have much torque at low rpm's without boost. I'll bet that most modern fuel injected 3 litre V6 gassers would have about the same amount.........but they have the advantage of rpm's and the resultant benefit of gearing to put the torque to the pavement.

My thinking is probably erronious but, it seems like a little more fuel earlier on would help to spool the turbo a little sooner making boost earlier etc, etc... A smaller turbo or VNT is probably the correct answer but, in all honesty, I don't ever see myself attempting that sort of project.

I think (actually I know!!) these turbodiesel engines are optimized for use in front of an automatic where the torque converter allows the engine to run up close to the torque curve and make decent boost and power. My '84 300D is a perfect example; at almost 300k miles, it has amazing snap and acceleration for a 3500lb car with only 100something hp.

I fully realize that I'm asking a bit more out of my wagon than Stuttgart probably intended but, just like installing a manual tranny, it seems worth exploring.

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Never a dull moment at Berry Hill Farm.

Perfectly true. The hi-stall torque converter will allow the engine to run right up to 1500 rpm off idle if you mash your foot. The time until the boost comes on is, therefore, that much shorter.

There is nothing wrong with your idea of dumping in a bunch of fuel to take advantage of all available air and potentially give you some reduced time to boost. But, I'd be doubtful if you could get much more performance from the vehicle if you used the unique approach of 10 psi boost versus the traditional approach of maxing out the ALDA fully CCW.

Only a test will tell.........

I should have mentioned this earlier: the ALDA on my wagon is currently maxed out CCW....little/no visible smoke under acceleration.

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Never a dull moment at Berry Hill Farm.

This begs the question........is the ALDA functioning properly??

Mercedes did a great job building these cars. Why does everyone think they slacked off in the engine tuning department? Maybe for emissions?

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1976 BMW 2002- 100k
1995 BMW 325i 175k
1984 Mercedes Benz 300D Turbo Diesel- 270,000 mi

1981 Mercedes Benz 240D- Estimated 300,000+ mi Returned to the earth

Good question.

Since there's no room for adjustment on the ALDA screw, maybe I need to add some shims under the ALDA and begin the readjustment process.

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Never a dull moment at Berry Hill Farm.

The aneroid capsules compress with higher pressure.

I really like how it drives right now. Yes, it will smoke if I drive it hard. With a little time, I'm learning to adapt to driving with the more sensitive throttle and putting out little/no black smoke.

Depending on how the IP reacts when I adjust the full load settings, I might have to put the aneroid back on. If the full load is much higher the IP could give even MORE fuel at the low end and be too sensitive to drive without black smoke.