Automotive/79 mercedes 300 cd

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Expert: - 3/18/2010


Question
Can't get it to start.  240000 mile with no problems. runs great.  Not a primary car.  Changed the motor mounts drove 100 miles or so parked it for a few weeks.  Battery dead, normal has a slow drain I put a battery switch to save the battery while it sits and forgot to turn it off.  Charged it and now it won't fire up.  Was low on fuel but not out.  Checked the inline filter has fuel.

What else?

Answer
Not sure from your query whether the battery is able to even crank the engine, or whether it can, but the engine does not start.  If the former applies, it could be that the battery was damaged by sulfation due to the deep discharge of being left connected.  The battery must first operate the glow plugs prior to cranking the 2kW starting motor, so any battery used must be in serviceable condition.

If the problem is the latter, I would prime that injector pump if you have not done so already - being an owner of this car, I would imagine that you are well familiar with the process of priming the injector pump by opening the bleed nut atop the main fuel filter and then operating the hand pump until any air in the system has been vented and fuel has started to exit via the bleed nut.

One hopes too that the stored fuel is still reasonably fresh.  Diesel fuel does go stale fairly quickly, although this can be mitigated by the use of fuel stabiliser fluids appropriate for use with Diesel fuel.

The OM617 engines tend to start fairly reliably even if the glow plug circuit is not working, but tends to be argumentative unless you have a good feel for maintaining sufficient fuel flow to get past an initial rough idle.  The glow plugs themselves are quite cheap to change out if new ones are needed, but do require some box-wrench dexterity due to their proximity to the injector lines and control linkages.

Hope the foregoing helps!  Mine is just about 257000 miles now.  The timing chain and guides were changed out at 197000, and adjustment is recommended every 15000 miles or so, along with valve lash adjustment - these are good preventative maintenance tasks by which to maintain performance and reliability.

Cheers ... EGK

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Ernest (Ernie) Kenward

Expertise

The challenges I most enjoy are thoughtful technical questions of a trouble-shooting nature in both electrical, power electronic and mechanical systems, mainly automotive but also machine control and small-machine PLC applications. Please note, however, that I am NOT a walking shop manual! I DO, however, make it a point to have those manuals and other service literature for those vehicles I DO own, and highly recommend that anyone serious about maintenance or modification of their vehicles do the same; MOST of your answers WILL be found there. For that matter, I do NOT go out of my way to acquire shop manuals for any vehicle I do NOT own! That being the case, any general query to me along the lines of "What is the meaning of this code read from the ECU of my 2015 XYZ?" or "Where is the fuse for the windshield washer pump found?" (try your car's electrical distribution panel for a start!) will not go far. What I do offer is a pretty good collection of literature, insights and hands-on experience with 1950s to 1980's Ford products (plus a developing database of information and practice with the Mercedes diesel cars), along with an engineering perspective and the ability to design and implement custom control, electrical and mechanical subsystems for vehicles. For that reason, I am happy to make my thoughts and efforts available to those who are of like mind and/or are seriously making a point of learning about their vehicles. Use the Opportunity to Learn!

Experience

A key skill in my work and hobby pursuits both is STRATEGIC TROUBLESHOOTING. I am a senior instructor in Electrical Engineering Technology at a leading Canadian polytechnic, my areas being Electrical Power and Industrial Control, electrical and electronics design and manufacturing, and AutoCAD and related CAD/CAE software - plus equipment problem-solving and new equipment design and prototyping. Hobby-wise, I have 30-plus years of experience in auto restoration, mostly in electrical and mechanical systems. Ongoing projects include a 1959 Edsel Corsair, my 1978 Ford E250 class-B motorhome conversion, and the care and upkeep of my Mercedes 300CD. My vehicles become engineering test beds for electrical and mechanical upgrades as ideas present themselves. This includes the design and production of circuit boards to restore or enhance features for which no OEM replacement parts are obtainable, or where better specifications or reliability can be had via newer concepts. Regarding the E250 RV conversion, I designed and continue to revise a custom power distribution system, managed by a Programmable Controller (PLC); this has made most revisions as easy as uploading new firmware as I develop it. The "mini" PLC is a powerful device for custom automotive control systems. One good example (there are many) would be the Moeller "Easy Relay"; these offer a wealth of control, monitoring and variable-and-status display options for such projects. A good example project which has worked well is that one for my RV noted above, which has been on the job - revised in firmware only - for a decade now. It is a load management and charging control system to avoid the sulfation-induced early failure that often befalls deep-cycle batteries used in RV power applications. The battery installed in 2003 lasted long enough to more tnan pay for the PLC that contributed to its longer life ... and the PLC will be there for the next battery as well!

Organizations
IEEE - senior member ... past WCC Student Activities; SME - senior member ... past chair, greater Vancouver chapter chair 318; Edsel Owners' Club - have served in various capacities on chapter executive during seventies; have been Power and Driveline resource on the Edsel Owners' Club "E-team" for more than a decade.

Education/Credentials
Graduate of UBC

Awards and Honors
Certificates of appreciation from IEEE and SME for work in student and chapter activities

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