1980 450SL K-Jet poor acceleration

[rmasteller]

I am going to start troubleshooting my poor acceleration in my 450SL. Since ACC and door vacuum doesn't seem to work, I thought they may be impacting the distributor or other engine systems. I looked up vacuum diagrams and it seems that the engine/emissions diagrams never show anything about ACC or doors. Are these vacuum systems isolated from each other? It would be a good idea, of course! Just confirming.

I'll have to time it, but the 0-20 or 0-30 acceleration on my car is terrible. Otherwise, running well. Transmission holds 1st gear for a while, then once in 2nd gear it goes quickly to 3rd gear. But, the sluggishness I'm out to correct is a lack of off-the-line performance.

[rmasteller]

Found another link that I like:
https://www.peachparts.com/shopforum/mercedes-benz-sl-discussion-forum/225532-80-450sl-poor-acceleration-aux-fan.html

I have a 230SL and we have some standard procedures to make sure systems are set to factory spec to get an engine to a good baseline before troubleshooting. There's a good list in the thread to try to get the engine to a good baseline, but some of it is replacing parts instead of setting things to spec or testing systems. Some of the parts I've already done. From other threads, I'll need a timing light to check distributor advance at various RPM. Once I get confirmation that the vacuum system for the ACC and doors are not involved in the engine, we can work on these items and more. Thanks in advance!

Start with the basics if you haven't already:
Plugs/wires/cap/rotor
Replace air filter
Set engine timing to 5 deg. btdc
Test Fuel pump and replace the filter
Check/replace ignition coil
Check all Engine Vacuum lines for leaks
Adjust air/fuel mixture

[Frank Reiner]

rm:

Is this car new to you? If not, is the sluggishness a sudden occurrence?

1st steps: A compression and/or leak-down test. Then check that both centrifugal and vacuum advance functions are working.
Once the condition of compression and the ignition system are confirmed, then the fuel system can be addressed.

[rmasteller]

I've owned the car 10 years, but after changing the daily driver from a 97 E300 diesel to a 17 C43 AMG, this sluggish acceleration is finally annoying. The car will cruise at 80mph, even up hill, if that helps.

I can do a compression test, done that before on other cars. What equipment is required for leakdown test?

All I need for the centrifugal and vac testing on the distributor is a timing light, correct?

Are the vacuum systems separate?

[Frank Reiner]

Originally Posted by rmasteller

I can do a compression test, done that before on other cars. What equipment is required for leakdown test?
All I need for the centrifugal and vac testing on the distributor is a timing light, correct?
Are the vacuum systems separate?

If the compression pressure test were to show a large variance between cylinders, then a leakdown test would be in order. A leakdown test involves pressurizing each cylinder with the piston at TDC, and observing the pressure drop, and also listening for sounds of leakage.

The simplest test for centrifugal advance function is to remove the distributor cap, and check for free rotation/springback of the rotor. The motion of the rotor should be about 15 degrees. The vacuum advance/retard control can be checked with a vacuum pump of the "MightyVac" type. With the dist. cap off, and vacuum applied to each side of the unit, movement of the magnetic pickup should be observed.
A timing light will be required to check the firing point(s).
The distributor vacuum is separate from the chassis system.

[rmasteller]

Thanks for the details, Frank. I have a MightyVac. How much vac should it pull to activate? I'll have an update after a week or so. Several things going on.