"Conversely, If the ALDA is adjusted for too much fuel, there will be excessive fuel that can't be burned at full load and speeds above 4K RPM and will end up lowering combustion temps and creating more smoke....BUT max boost pressures *will* have been achieved"

NO NO NO NO!!!!! Too much fuel raises combustion pressures and temps to the point where things melt. The relationship between rich/lean is exactly the opposite in diesels and gassers. Run a gasser lean you get lots of power and melted exhaust valves, scored cylinder walls, melted pistons, etc. Run it richer and she cools down makes good power, more fuel-cooler still and power drops off. Diesels keep making more and more power as you add more and more fuel until they overfuel and start melting things. RT

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I couldn't agree more. I am not advocating just adjusting here and there without regard to results. I see no issue with adjusting boost to the high-end of the factory spec either with a Dawes or just the factory wastegate. The increase in boost will simply allow the ALDA to provide the factory-specified maximum fueling and the result will likely be a very good running MB. A small adjustment to the ALDA will LIKELY cause no harm but I did so with the full understanding of the consequences. Believe me when I am towing heavy with the truck, my foot to the boards I think I watch the EGT/Boost gauges more than the road! That engine is operating at the ragged edge of its design parameters. I am okay with that as I know what the limits are, I know what the consequences are and I am carefully watching to make sure that critical limits are not exceeded. All I ask is that people fully understand how things work before they go tweaking here and there. That they understand the risks and they know the limits of their machinery, monitor it with quality instrumentation, so that "ugliness" doesn't occur. RT

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But, What about the GLOWING WHITE HOT SOOT DEPOSITS on the Di-fusser Balls in the Pre-Chambers which result from EXTREMELY RICH conditions, which by the way reaches this state on SPOOL DOWN . . . AFTER the accelerator is released as the TURBO winds down . . . Like using a blower to get your charcoal lit . . .

You hit the nail on the head. EXTREMELY RICH conditions..... Thats what'll happen if you go messing with the ALDA and turn the bloody thing ALL the way out and then continue to operate without EGT/Boost gauges. If parts are getting that hot it WILL be indicated in excessive EGT's. It will be obvious and even a chimp would know to get off the right pedal. RT

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Just the OPPOSITE happens as the BOOST PRESSURE DROPS during SPOOL-DOWN, the SOOT gets blasted with a LEAN mixture as the TURBO winds down causing it to GLOW WHITE HOT as the FUEL is CUT OFF when the throttle is released . . .

Actually I get your point completely. When you get off the pedal the engine does indeed go lean but that is not what causes the "white hot glowing". What causes this is the immediate lack of BOOST!! Boost has a cooling effect beyond just stuffing more air into the cylinder. The higher the boost pressure, the better the cooling-to a point. Thats one of the reason intercooling works. It allows higher fueling rates while controlling combustion temperatures. Higher rpm will also lower EGT/combustion temperatures simply because there is more air passing through the engine and cooling it!! I have seen EGT's spike up when downshifting just as you describe because I have cut fueling and therefore boost momentarily for the shift to occur. The trick is to not run so hot that the EGT spike exceeds the limits of the engine when the shift happens or you have to get off the right pedal. The case you describe with "white hot glowing" has to be a very extreme example of a motor operating way beyond its design parameters. In order for this to occur the EGT's during operation must have been WAY WAY beyond safe limits to begin with. Which, if I may make my point again, would have been completely avoidable IF the operator had EGT/Boost instrumentation and knew what they were looking at. RT

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There's a LARGE HEX fitting under the ANEROID COMPENSATOR (ALDA) . . .

I believe it's 30 or 32mm . . . and a HEX cast onto the aluminum housing of the ANEROID which you'll need a THIN wrench to keep the ANEROID from turning while breaking the FITTING loose. A pair of LARGE Channel-locks will work to hold the ANEROID while turning . . .

To LOOSEN the fitting, turn CLOCKWISE viewed the TOP looking DOWN . . .

CAREFULLY lift the ANEROID off making sure that NO SHIMS stick to the bottom of the ANEROID and fall off and get lost . . .

Then, look down INSIDE the FITTING on the PUMP to locate any shims . . .

There may be 1 or MORE shims . . .

FIRST . . . MEASURE and RECORD the SHIM/S THICKNESS and keep the data in the glove-box . . .

Contact a Bosch Pump Service for shims or you can use WASHER/S which you can file to get the desired dimension . . .

START with the ORIGINAL SHIM DIMENSION and ADD in .5mm (.020") increments until you either notice SMOKING and/or UNDESIRABLE FUEL MILEAGE, and work BACK-WARDS by DECREASING the dimension until you get the DESIRED RESULTS . . .

This way you can ALWAYS go back to the STOCK CALIBRATION by re-shimming back to the ORIGINAL SHIM DIMENSION. . .

Mpnye,
I reread the threads and cannot find what you are refering to. I understand that altitude plays a big part in messing with the ALDA. Thats why I keep pushing the use of instrumentation to monitor your engine. You never know when a factory failsafe might fail and cause serious engine damage..... I certainly would like to know how to do the mentioned "aneroid shiming". How about a DIY post? I'm a big boy and can accept the consequences of screwing up so hows it done? Whats it done for? What exactly does it do? I sure would love to know... RT

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Mpnye,
Now that is excellent info!! Thanks! Since you seem to know about the inner workings of these pumps, what is the difference in making this adjustment as opposed to adjusting the screw on the ALDA like everyone likes to do? I am guessing that a shim results in a linear change to the fueling curve whereas adjusting the screw changes preload on a spring and therefore would be a progressive change to the fueling curve? Thanks, RT

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"Conversely, If the ALDA is adjusted for too much fuel, there will be excessive fuel that can't be burned at full load and speeds above 4K RPM and will end up lowering combustion temps and creating more smoke....BUT max boost pressures *will* have been achieved"

"NO NO NO NO!!!!! Too much fuel raises combustion pressures and temps to the point where things melt. The relationship between rich/lean is exactly the opposite in diesels and gassers. Run a gasser lean you get lots of power and melted exhaust valves, scored cylinder walls, melted pistons, etc. Run it richer and she cools down makes good power, more fuel-cooler still and power drops off. Diesels keep making more and more power as you add more and more fuel until they overfuel and start melting things. RT"


RT....I'm still not convinced on this point. Given a fixed engine condition, an increased fuel ratio will not be able to be burnt completely w/o additional oxygen. This unburnt fuel is my reasoning for the lowering of combustion temps.
It's only when boost pressures are INCREASED that the oxygen levels are increased thereby allowing the higher fuel ratio to be taken advantage of.

If I'm missing something here....it's a doozy.

Chris
'85 300SD

OK . . . this is my LAST reply to this thread . . .

(a) Look at the ANEROID COMPENSATOR (ALDA) as an INDIVIDUAL COMPONENT which has a FACTORY CALIBRATED CURVE to INCREASE the FUEL DELIVERY PROPORTIONATE to ALTITUDE and BOOST PRESSURE CONDITIONS . . . PERIOD ! ! !

(b) NOW add additional factors such as ENGINE RPM and LOAD relating to FUEL DELIVERY TIMING ADVANCE from the CENTRIFUGAL TIMING ADVANCE DEVICE in the engine and THROTTLE POSITION.

(c) ALL these factors are being processed along with GOVERNOR, RIV and RACK POSITION SENSOR INFORMATION within the INJECTION PUMP to determine HOW MUCH FUEL . . . WHEN ! ! !

By RE-SHIMMING the ANEROID, the MIXTURE is being ADDITIONALLY ENRICHED EVENLY ACROSS THE ENTIRE ENGINEERED CURVE RANGE in relation to PRE-DETERMINED BOOST/FUEL DELIVERY CORRELATION . . .

By RE-SHIMMING, WHEN remains the SAME . . .

HOW MUCH . . . is what's being CHANGED . . . PERIOD

Mpnye,
Thanks for the clarificaiton on the adjustment. Your way seem to be a better way to go provided you monitor the results.

ck42,
A gasser is supposed to run "optimally" at an air/fuel ratio of about 14.7/1 (stoichiometric sp? ratio I think its called) wether at idle or WOT. (Reality is max power comes at ratios @12.5/1 at WOT, but thats another issue...) A diesel at idle is something like 125/1 air-to-fuel and full-power under load not usually more than 25/1. The answer is there is ALWAYS enough air in a diesel to burn all the fuel, its not lack of air that is the issue. The issue is how long it takes to burn the diesel fuel. As fueling increases so does the window of time that the injector is open. This causes later and later injection periods and incomplete burning of the fuel. The fuel continues to burn as it exits the cylinder and into the exhaust system, because there is EXCESS air available to do so. The black smoke you see is caused be incomplete combustion and combustion that is occuring in the exhaust system. The fuel is still burning but not in the controlled manner it should be. In a gasser running richer uses all the air so that is why they run cooler. No excess air, excess fuel can't burn and you can smell it in the exhaust. One of the reasons higher-flow injectors make more power is not that they inject more fuel but that they do so in a much shorter TIME, allowing a more complete burn while keeping EGT's in check. This is a tough concept to grasp. high-volume injectors can often make a difference on even a stock engine at stock fueling levels. The reason is they inject the same amount of fuel but they do so in a shorter period of time allowing more time for the fuel to burn. This is a bit simplified and generalized as many factors affect EGT's, burn times, etc. such as chamber design, bore/stroke, type of injection system, etc. Clear as mud! RT

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