P.E.H. that is what I thought, Fisherman may have been mistakenwhen he said I still need to ifentify the adjustments on my IP, to alllow me to adjust the idle and max fuelling.
Any clues?
I do not wish to adjust by trial & error
Too much chance of major error
Tony

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Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.

Tony,
That pump doesn't look anything like the pumps produced for the U.S., so I can't help you.

Fisherman,
That adjustable nut on the back of the pump is not there to adjust fuel delivery. It is there to be adjusted to just touch the rack and reduce bounce of the rack, which can cause a rolling idle. Those back plates with the adjustment weren't even on the first cars. It was a factory mod. The cars were called in, and the plates were replaced at factory expense. You have probably forced the rack prtially to the shut off position which is why you lost power.

Peter

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Auto Zentral Ltd.

My 75 240D had a M-Style pump with the pneumatic governor and it did not have a rack dampener bolt, it had an adjustment bolt on the back of the IP that controlled max fuel delivery by acting as a stop for the rack when it went to full throttle based on the manifold vacuum and governor spring adjustments. I adjusted it slightly clockwise and reduced my smoke dramtically but this is not a Rack Dampener which is I believe what was being metnioned in the previous post.

On my 1980 300D N/A it had an MW style pump which had the alda on top of the pump. I know because I replaced it when I swapped IPs off another car.

That pump in the picture does not look familair to me but then I have only had four MBZs in my stable and the current two are basically the same car.

PEH, I think the positive manifold thing is only true when you have a turbo. The N/A versions should still have an alda to adjust fuel delivery amounts when traveling from sea level into the mountains. Otherwise you would generate a lot of smoke at 5000 feet when you have no smoking at sea level. This is speculation though on my part...

The thing that tipped me to the adjustment on the M-Style IP on the 240D was when I went down to the SF Bay Area and the car did not smoke a lick yet at home it used to blow clouds (and I mean clouds!). I think the PO dialed up the fuel delvery to try to get more power, which worked, but the result was a lot of smoke from unburned fuel at my 3200 foot elevation. Credit is due to this forum for helping me figure out that it had this fuel adjustment. I do not believe that the other pumps have this as an external adjustment therefore without a bench and the proper equipment I don't think you could do this yourself without really messing up other components...

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

Turbo engines have an ALDA, which compensates for both atmospheric changes AND boost pressure changes.

Non-turbo engines have an ADA (note the missing "L") which looks different, and only compensates for atmospheric changes.

Here is the deal regarding power and altitude:

The atmospheric pressure at sea level is 14.7 psi. This pressure is increased by 12 psi from the turbocharger to a total of 26.7.

The atmospheric pressure declines as altitude is increased based upon the following formula:

14.69 (((518.7-(.00356H))/518.7)^5.256)

In this formula, H is the altitude in feet.

So, if we substitute 6200 for H, we get: 11.69 psi

Now, on a naturally aspirated engine, the power for 6200 feet is 11.69/14.7 which equals 79%.

On a turbocharged engine the pressure at 6200 feet is 11.69 plus 12 psi from the turbo for a total of 23.69. The power on the turbocharged engine is 23.69/26.7 which equals 89%.

When you drive the turbocharged engine below 2000 rpm, without boost, you suffer the same losses as all the non-turbo engines: 21% power loss. However, once you hit boost, the additional power feels tremendous because you have now cut your losses to 11%. The vehicle still has less power than it would otherwise have at sea level, however, you feel the difference between 79% and 89% and determine that the turbocharged engine is fine once you get the boost.

As the altitude is decreased, the difference between the naturally aspirated engines and the turbocharged engines is also decreased.

At higher altitudes, such as 10,000 feet, the difference between the two engines is very pronounced. The naturally aspirated engine has 68% and the turbocharged engine has 82% of sea level horsepower.

Brian,

The 26.7 PSI you mentioned is controlled by the wastegate. So if the turbo is strong enough, it could maintain the same pressure at altitude up to the point where the air is too thin for the turbo to maintain the 26.7 PSI.

I don't know how power much I lost near Vail CO, but everyone else lost a lot more because my '80 300SD was passing everything on the road, even V8s.

P E H

PEH,

I believe that the 12 psi is controlled by the wastegate. You can get 12 psi all the way up to about 10,000 feet or so. However, you cannot get 26.7 psi because the atmospheric pressure is falling as you climb. Now, if you were to dial up the turbo above 12 psi, then, you could, in theory, get your 26.7 psi at higher altitudes.

I've read in a couple of different places that a turbocharger can fully compenstate for reduced oxygen up to about 8,000-9,000 feet, higher than this you will feel some drop-off in performance but the effect is not dramatic. It's fun to watch normally aspirated 454's fall flat on their faces while my Dodge-Cummins rockets past them on long high altitiude climbs.

Once up to speed there is very little performance loss due to the turbocharger compenstation, however it can take quite a bit more time to get the engine up to full boil.

Your mileage may vary...

If the turbocharger puts out a fixed pressure differential (say 12 psi) it does not know that the atmospheric pressure is dropping.

If the atmospheric pressure is dropping then the absolute pressure in the manifold is dropping.

If the absolute pressure in the manifold is dropping, then the power is dropping.

The only way that the engine could possibly maintain sea level power is if the turbo had altitude compensation so that it put out higher pressure at altitude.

With regard to the Cummins, doesn't the turbo put out some hugh amount of boost, like 35 psi or so? If this is the case, then please run the aforementioned calculations again for this level of boost. You will find that the the Cummins would retain 94% of its power at 6200 feet. You will hardly notice the 6% power loss.

Brian,

There is a difference between absolute pressure and gage pressure. Absolute pressure at sea level is ~14.7 PSI but a gage reads that as 0.

So if you have a gage on the manifold at fullboost it will read 12 PSI. But 12 PSI at 10,000 feet is still what the engine will see, regardless what the actual atmospheric is. The engine will continue to see this pressure (as long as its revved up) up to the point where the capacity of the turbo charger cannot keep up with the decreasing atmospheric pressure.

Its just like an air compressor. If the gage reads 100PSI, that is the pressure in the tank regardless of the out side pressure.

P E H

The absolute pressure in the tank would be 114.7 PSI since, as you point out, the pressure guage is calibrated to ignore the 14.7 PSI of atmospheric pressure.

I'm with PEH on this one - I'm pretty sure if you are climbing a mountain at 10,000 feet in Colarado and your boost guage indicates you have 10 PSI of boost you have the same amount of oxygen in the system as 10 PSI of boost at sea level.

The capacity of the turbocharger is far in excess of 12 PSI - this is why we have a wastegate and a control mechanism to ensure the engine is not overboosted.

Brian,
Thanks for the excellent explaination. You answered a question for me. I have gone camping at Carson Pass which is between Ca. and Nv. The pass is 10,000 ft. I felt that the turbo performed well as at sea level, but it appears the 10% or so was not noticeable especially with your ears popping and all that. I always ran it up hills in S instead of drive thinking I was getting power from a lower gear. Now I realize I was keeping my boost pressure up and keeping the turbo alive. Thanks again.

PS For all you Texans and Floridians out there, high altitudes cause poor hearing and ear popping until one's head clears itself and adjusts to the new elevation.

Peter

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Auto Zentral Ltd.

Tim, you are correct. The absolute pressure in the tank would be 114.7 at sea level. The absolute pressure in the intake manifold would be 26.7 at sea level.

At 6200 feet, the absolute pressure in the tank would be 111.7 and the absolute pressure in the intake manifold would be 23.7.

The turbo cannot know that you are climbing a mountain and the absolute pressure is falling. It only provides relative pressure. It will provide 12psi all the way up to about 10,000 feet, if that is what the wastegate is set at.

Brian

I think I see where our differences are coming from, let me ask you another quick question....

If the engineers in the fatherland built the boost control system on our cars to permit a maximum absolute boost pressure of 26.7 PSI (14.7 psi atmosphere + 12 additional boost) would we be able to get 26.7 PSI absolute in the Colorado mountians?

Only if you increase your boost pressure 2-3 psi, the difference in the elevation. You may not have the same quantity of oxygen due to the increased temperature and lower density of the compressed air. Intercooled it's totally capable of retaining sea-level performance - this "constant elevation" tuning is commonly done on higher-altitude aircraft.

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'83 240D with 617.952 and 2.88
'01 VW Beetle TDI
'05 Jeep Liberty CRD
'89 Toyota 4x4, needs 2L-T
'78 280Z with L28ET - 12.86@110
Oil Burner Kartel #35

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