IP shim and Non Turbo 617 at high altitude
 

Hello everyone. I own an '84 300TD US market /w turbo and auto transmission. It does seem to have a bit more acceleration than some other W123s I've driven. A mechanic said he thought it had a 'shim' in the injection pump which gave it a little more off idle response. I don't know the specifics of it and he didn't elaborate. Can anyone shed some light on this?


I do want to aquire a Euro model 300D with manual everything mainly because it lacks the automatic climate control, auto trans, power windows and self leveling suspension that can all be problematic. On my 300TD I have experienced frustrations with all of these things to some degree so I want some simplicity. I have driven my turbo wagon at high altitude and it does quite well once the turbo spools up. Can anyone tell me how I might expect a non turbo manual transmission 300D to perform at high altitude? Thx in advance

The shim is likely under the ALDA. It will cause the fuel enrichment to occur sooner instead of waiting for the turbo to spool to a higher manifold pressure.

Define "high altitude". The turbo cars are much better at high altitude since they compress the manifold to the same pressure as they do at sea level. An N/A is going to lose horsepower the higher you go and the drier the climate. Keep in mind the Turbo made 123HP compared to the N/A's 79HP and much more torque. It may not be as important in a sedan, but in the heavier wagon it matters.

I'm at 2100 ft in elevation (certainly not high altitude) in a fairly hilly, but certainly not mountainous area. Our climate is considered semi-desert, typical summertime humidity levels are <20% with temps in the high 90s and low 100's. I test drove a manual N/A sedan once when I was car shopping and while the stick was certainly nice (I love manual cars), the lack of power kept it from easily keeping up with highway traffic on the hills. The 240D I test drove was hilarious trying to climb the 12% grade outside of town. Settled on a turbo and wound up with an SDL and have had 0 problems keeping up with even 85mph traffic. The turbo makes it easier to keep pace if you let it spool a bit before you really need it when climbing a long steep hill.

Just my opinions...

Back to the basics.

The sort story is that as a non-turbo Mercedes Diesel continues to gain altitude performance will eventually drop off because the aneroid (I don‘t know the Mercedes name for it but it works off of the atmospheric pressure) will cut back on the Fuel as you go higher up because there is less Oxygen molecules per square inch the higher up you go.
If you added a turbo to the above system that would take care of the air density issue at higher altitudes but the aneroid still would cut back the Fuel at higher altitudes because it does not work off of manifold pressure.

The ADLA on the turbo Fuel Injection Pump works off of manifold pressure and in the face of atmospheric pressure the fuel is cut back. As the manifold pressure rises the ADLA allows more fuel to be injected because the extra fuel can be burned as there is a higher Oxygen (air) density being pumped into the cylinders.

So any shim has nothing to do with anything except the normal setup of the fuel when they run the Fuel Injection Pump on the test stand.

If your remove the ADLA the Fuel Injection Pump will put out the max fuel all of the time regardless of the manifold pressure the turbo creates.

People have few issues with their Turbochargers or the ADLA so it is not normally an issue.

As long as your Air filteration system is working propery your Turbo should be protected from damage to the Compressor Wheel.
While it seldom happens Oil leaks due to worn seals in the Turbo is the most common issue that people deal with but, most people have been able to replace the seals and bearings with out difficulty.

It is rare for an ADLA (it has a metal diaphragm inside) to crack.

I wouldn't worry about it. The euro 300d of that era has more pep than the us spec non turbo. My 300d euro would run 100 mph pulling 307 gears, in either fourth or fifth gear. The turbo cars will do about 110.