450 SL DIY question

[pj67coll]

As a general rule, of the 450 motors which is the easiest for a DIY individual to maintain? The earlier ones with the ECU (brain) running everything or the 77 and on with the mechanical fuel injection?

- Peter.

[Diseasel300]

Having lived with a Euro 500SL with K-Jet for 20 years, the K-jet cars can be a nightmare to troubleshoot if you don't understand the system. "Think like a German" has never been a more applicable statement when troubleshooting the K-Jet system. Add in the emissions controls that the US models used, and I'd rather kill myself than troubleshoot a problem.

[daantjie]

I would take K Jet over D Jet any day of the week.

[Frank Reiner]

Originally Posted by pj67coll

As a general rule, of the 450 motors which is the easiest for a DIY individual to maintain? The earlier ones with the ECU (brain) running everything or the 77 and on with the mechanical fuel injection?

- Peter.

The K-jet engines from 1976 thru '79 have purely mechanically controlled injection; 1980 has a Lambda sensor and feedback control of mixture.
The '77-'79 models had an under-floor cat, rather than engine mounted cats, and would be preferred for that reason.

[pj67coll]

I know about the cat issues. My thoughts revolve around having to maintain such a vehicle as a DIY project. Pretty much any mechanical aspect of the vehicle is similar to any other Benz of the era and ultimately could be addressed in a remove/replace fashion, wether from junkyard parts or what ever source one can find. But my assumption is that the most complex aspect of these from that era is the fuel injection system which would be the most troublesome to keep messing with on a daily driver basis. (Well, more of a weekend toy than a true daily). So that is why I'm trying to see if there is a real difference between the two systems in terms of DIY complexity. Does the later Lamba sensor addition make the K-Jet as bad as the D-Jet?

- Peter.

[Frank Reiner]

Originally Posted by pj67coll

Does the later Lamba sensor addition make the K-Jet as bad as the D-Jet?

- Peter.

No, it just adds a sub-system that consists of a sensor, a processor/driver, and a solenoid valve (aka, frequency valve). As with all of these systems, age has its influence.

By way of a separate thought, a D-jet system converted to operation with a modern, aftermarket ECU (think Megasquirt) gets around the original D-jet limitations.

[fonzi]

Used regularly, I’d bet an early k-jet is less prone to failure or the need for maintenance. D-jets will likely have solid lifters and points each needing adjustment. Plus other parts more prone to failure. I do like the system better than a k-jet for some reason. Something very “vintage” about maintaining it.


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[Graham]

Originally Posted by fonzi

Used regularly, I’d bet an early k-jet is less prone to failure or the need for maintenance. D-jets will likely have solid lifters and points each needing adjustment. Plus other parts more prone to failure. I do like the system better than a k-jet for some reason. Something very “vintage” about maintaining it.

Glad to hear you like the Djets Fonzi

One big plus for the early D-Jets, is that they don't have the plastic timing chain guides that all 107s after 1973 have. Those guides are prone to failure, sometimes catastrophic and changing them is no easy task.

I have only owned Djet. It certainly lends itself to the DIYer. Parts can be a problem - they are available new and used, but prices have been climbing. It helps to have spare ECU, MPS (manifold pressure sensor), Trigger points (or complete distributor) and AAV (aux air valve). A means of checking mixture such as a CO analyser or AFR instruments is a big help in fine tuning. Replacing ignition points with a Petronix is always a good move.

Personally, I wouldn't swap my Djet for a K-jet. May be a case of better the devil you know But really, I have had my Djet for almost 30 years with minimal problems. No shops understand them anymore, so you NEED to be a DIYer!