1984 Mercedes 300D Tune-Up

The Italian Tune-Up

The Italian tune-up - at least in a diesel [although it applies to a gas car too - Ed] consists of taking a SOUND car out and maximally accelerating from stop or slow speed to some high speed OR driving at near full rpm with a heavy load (up long hill) for minutes at a time. The idea is to get maximal air and fuel flowing through the engine to develop near maximum heat. This will burn and eject residual carbon that has collected in the engine. Following such a regimen the idle is usually smoother and the amount of black smoke at full throttle should be reduced. This occasionally does not happen the 1st time and the idle might get rougher or a pronounced knock could occur. This is usually because some carbon has been "rearranged" but the prechamber environment isn't appropriate for smooth combustion. Further TREATMENT will clear this up as more carbon is burned up, but it is a little scary the 1st time it happens to YOU and your car!
A few full throttle accelerations a week will usually keep most CLEAN engines cleaned out pretty well. More prolonged "treatment" is usually required for a car that has had a LOT of city driving. Just a long highway trip (50+ miles) with several two-three minute full throttle periods (long 6-8% grades are GREAT) will clean out an awful lot of carbon and crud that's build up, but with a really "city bound car" it may may take more than just a few sessions to really get it all out. My weekly 250 mile trips from Pittsburgh to Washington DC and back over the last 7 years have given me a chance to really examine the "Italian tune-up" and the concept of "flailing the heck out of the MB diesel engine" or at least running it at near full throttle/top speed for a long period of time.

I referred to a "SOUND" car. To me that means a car that NO serious mechanical problems. The chain stretch should be below 5 degrees or so, the valves should be properly adjusted, the air and fuel filters should be verifiably clean, and there should be clean and it would probably be best if the injection pump timing is known to be pretty close to correct (within a couple of degrees). The cars/engines I presently own, have THRIVED on this regimen. Idle smooths out, smoking diminishes, and fuel and oil consumption goes down. I can't promise that on an engine that's worn out, but nobody else can either ;-)

Marshall Booth

Thanks for the info, Bob!

It's also either leaking or burning about a quart of oil every 500 miles. We really need to go through that engine compartment with a fine tooth comb and see what's leaking.

I swear we picked up 15hp doing a proper valve job. It's a bitch without the proper wrenches. We bought some cheap wrenches and modified them ourselves.

The other thing that is huge is injector nozzels. It was about a 2 hour job for one person. The car went from missing at idle, to idling beautifully. It also comes off idle much better.
https://mercedessource.com/store/5-cyli … at-shields

If it's an issue(and it will be one day) the primer pump will die. Don't buy the cheap one. This one primes in like 10 pumps max.
https://mercedessource.com/store/heavy- … rimer-pump

While the injectors are out we did glow plugs. The car loves it some glow plugs.

This is about it we've done to our OM617 powered car, and you've seen how fast it is... We've also got a straight pipe!

It looks like the valve adjustment tool is just a crow's foot on a 3/8" drive extension bent in a lazy Z shape. Can anyone tell me how much the offset on the extension is? I'm planing to make my own. Just going by the pictures I've found, the offset looks like 3/4" or 1". I'm guessing it's not that critical, though.

So you're just using an open-end wrench with a bend? That will probably be easier. What size wrench?