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Thread: Mercedes 300D won't start

  1. #1
    Join Date
    Jun 2006

    Mercedes 300D won't start

    I've been having some discussion over on the Ozbenz forums about one of my 300Ds that is not starting, but for the benefit of all I'm posting up a summary here:

    One of my WVO powered 300Ds has been getting progressively difficult to start, and the last couple of days I haven't been able to get it to start at all. It has also been idling rough for some time. I'm a bit worried it's something major like the IP, as I've checked all the obvious things. I'm wondering what else I can check to try and narrow it down a bit before major surgery.

    When I turn it over it coughs on every revolution of the engine, but never catches. I've tried a quick squirt of WD40 and a capful of methanol which has worked previously on cold mornings, but it makes no difference. It doesn't even that start then die (as I would expect if it was a fuel starvation/air leak problem).

    Things I've checked so far:

    • Fuel - I removed the return line and operated the primer pump - fuel is coming through easily with no blockage.
    • I've changed from biodiesel to dinodiesel in the startup tank. That made starting easier for a couple of weeks when the weather was cold, but now it's not starting even though it has warmed up.
    • Air filter is OK, and I've removed the filter cover to ensure there is no restriction
    • The glow plugs are nearly new, and I checked the voltage on all of them OK
    • Battery is good and I've charged it up again. I also tried jumping it from the other car to see if it would turn the engine over a bit quicker, but it didn't help.
    • I removed the vacuum line to the IP in case this was holding the engine stop lever down. I haven't removed the actuator to check inside, but I doubt this is relevant
    • No obvious fuel or air leaks

    Valve adjustment was done about 3 months ago.

    Injectors were changed for new Bosch ones only a few thousand km ago, although I didn't get them pop tested or adjusted. I will remove them this weekend to see if there is any carbon build up or anything visible.

    I was intending to adjust the IP timing using the "drip" method, but don't know if it would help. I was also going to give the water injection purge a go (as mentioned by Helga in another thread), but I need the engine running to do that!!

    Another thing to note - it was running a couple of days ago - so it's not as if it has been sitting idle for months.
    Since then I've removed the injectors and noticed a considerable build up of carbon on the nozzles and in the holes.

    My next plan is to do a compression test, try to get the injectors cleaned up and also lean out the IP timing before trying to restart the car.

    Any other suggestions would be welcome. The full thread with photos is here.

  2. #2
    Join Date
    May 2007
    central coast

    Re: Mercedes 300D won't start

    Interesting read Sean.

    Is this the car I spotted you in on the pacific hwy over 6 months ago.
    I made mentioned in a thread I spotted you and also made comment on the
    amount of smoke from the exhaust. It was peak hour traffic and slow going.

    Keep us updated and good luck.

  3. #3
    Join Date
    Nov 2007

    Re: Mercedes 300D won't start

    Hi pangit,

    it does not sound good.

    The increased carbon buildup since the injector change, engine not firing on methanol.

    A compression test would be the go.

    It sounds like there is not enough compression to fire up.

    It's hard to imagine a low km idi being coked up from wvo unless the rings were on the way out when you got it?

    Let us know how it goes,

    God bless froggo.
    HJ45 Landcruiser Troopy
    Home made 2 tank system
    Blending in main diesel tank
    SVO/WVO Converted 18/01/08

  4. #4
    Join Date
    Sep 2005

    Re: Mercedes 300D won't start

    I posted the following on the OzBenz thread:
    Perhaps the engine was significantly worn before using WVO.

    Pangit, Have you tried my suggestion of tow starting the engine to verify that there is not another cause for the failure to start? If it won't run, there may be a completely different cause, unrelated to engine compression.
    Were you able to perform cylinder compression tests? What were they?
    Have you checked the valve clearances?

    Without compression testing, dry and wet, you are just guessing about the compression as the cause of the failure to start.
    Froggo wrote:"Increased carbon build up since injector change"
    This is unusual, rebuilt injectors should have a good spray pattern, which should provide better burn characteristics, thus low carbon build up.

    Can we come back to the problem which caused you to change the injectors - poor cold starting.

    Poor cold starting usually indicates either GP issues, Injection problems or Low Compression. The new injectors did not improve cold starting.

    As the cold starting is worse now, and I presume that you have checked GP operation, the choices are low compression or injector pump problems.

    It is easier to check the compression first, as an IP overhaul will cost you ~$1000.

    A dry / wet compression test will differentiate between upper cylinder leaks and ring leakage.
    If you have access to a compressor and can adapt to the Injector or GP threads, you can do a "leak down test" to identify if the problem is with the inlet or exhaust valves.
    If compression is reasonable, you could check ignition timing to ensure that it is set correctly, as poor timing can cause poor cold starting.

    I hope this helps,

    Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

    Current Vehicles in stable:
    '06 Musso Sports 4X4 Manual Crew Cab tray back.
    '04 Rexton 4X4 Automatic SUV
    '2014 Toyota Prius (on ULP) - Wife's car

    Previous Vehicles:
    '90 Mazda Capella. (2000 - 2003) My first Fatmobile. Converted to fun on veggie oil with a 2 tank setup.
    '80 Mercedes 300D. 2 tank conversion [Sold]
    '84 Mercedes 300D. 1 tank, no conversion. Replaced engine with rebuilt OM617A turbodiesel engine. Finally had good power. Engine donor for W123 coupe. (body parted out and carcass sold for scrap.)
    '85 Mercedes Benz W123 300CD Turbodiesel
    '99 Mercedes W202 C250 Turbodiesel (my darling Wife's car)[sold]
    '98 Mercedes W202 C250 Turbodiesel (my car)[sold]
    '06 Musso Sports Crew Cab well body. [Head gasket blew!]
    '04 Rexton SUV 2.9L Turbodiesel same as Musso - Our Family car.
    '06 Musso sports Crew Cab Trayback - My hack (no air cond, no heater).

    Searching the Biofuels Forum using Google
    Adding images and/or documents to your posts

  5. #5
    Join Date
    Jun 2006

    Re: Mercedes 300D won't start

    Yes it is the same one Neil (the light blue one) and I have been aware of the smoky exhaust issue for some time.

    Anyway I'm getting a compression tester and will check it this weekend.

    The original loop style glow plugs were replaced with the pencil style ones less than a year ago and I have checked they are all working OK. It did not make much noticeable difference to the starting when I changed them anyway.

  6. #6
    Join Date
    May 2007
    central coast

    Re: Mercedes 300D won't start

    Any issues with your other merc.
    Compression test the two and if everything ok with your other merc may
    suggest issues before your converted it.

    If your other merc is fine you would think your setup and system is not the problem.

  7. #7
    Join Date
    Feb 2006
    Mount Gambier

    Re: Mercedes 300D won't start

    On my 2 mercs, the hard to start one also has the most blowby.
    Last edited by Captain Echidna; 11th June 2009 at 11:39 AM.
    cheers<BR>Chris.<BR>1990 landcruiser 80, 1HD-T two tank, copper pipe HE+ 20 plate FPHE, toyota solenoids and filters. 1978 300D, elsbett one tank system.<BR>

  8. #8
    Join Date
    May 2007
    central coast

    Re: Mercedes 300D won't start

    Can we get an update Sean.

  9. #9
    Join Date
    Jun 2006

    Re: Mercedes 300D won't start

    I got a cheap crappy compression tester and it showed low compression on all cylinders, but I'm not 100% confident in the results as I'm not sure it sealed properly. When I took out an injector on my other 300D I did notice it has heat shields whereas this one does not seem to, so I will try another compression test with heatshields, as the instruction says you are supposed to.

    I will also try swapping the injectors over to see if I can get it to start at least.

  10. #10
    Join Date
    Aug 2008
    wa. usa

    Re: Mercedes 300D won't start

    Compression should be at least 300 in all cylinders. Timing should be at least 24 before top dead center. Most of the old Mercedes are out of time. Have you checked your timing chain stretch? Are there any air bubbles in the fuel line? You could do a leak down test and see if the top end has a leaking valve ... any way just a thought

    Does the motor try to start (pop some times) or do you just hear the starter with not pops from the motor?

    Let us know what happens

    Here is some info

    The following page is a backup which was originally created by Richard Easley and Stu Ritter, all credit should be given as such. Most links on these pages are unfunctional.
    Injection Pump Timing Adjustment for 617 Engines
    The technical material for this FAQ (Frequently Asked Question) was provided by Jim Mahaffey of Georgia Institute of Technology (Georgia Tech) and other subscribers to the Mercedes-Benz Discussion List, was edited by Richard Easley of Baylor University, and is provided as a service to the subscribers of the Mercedes-Benz Discussion List.
    After getting excellent advice on the Mercedes-Benz Discussion List regarding injection pump timing for the 617 diesel engine (turbocharged 5 cylinder), I thought that it would be helpful to write it up for the benefit of others as a "one-stop" message that incorporates everything into one post. This method of timing is ideal for the do-it-yourselfer because no tools are needed.
    To receive similar quality tips as described below on a daily basis, consider subscribing to the Mercedes-Benz Discussion List, which is located at the following site:

    Using the categories of mechanical ability from the Mercedes-Benz Discussion List <>, you need to be at the level of "Medium Do-It-Yourselfer" at minimum. If you are below that level, you may want to provide these instructions for someone who is at the medium level or beyond.

    Tools needed for injection pump timing
    1. The procedure requires only a few do-it-yourself tools at Craftsman quality or above (we'll set the "floor" level on tools for do-it-yourselfer where Craftsman equals the minimum quality needed).
    2. Floor jack and stands
    3. 27 mm socket and long ratchet or breaker-length bar
    4. Heavy duty prybar
    5. 8 mm 1/4" drive socket with ratchet and long extension
    6. 8 mm closed end wrench
    7. 17 mm wrench
    8. 13 mm combination wrench (See #13 below which provides an excellent tool for this particular procedure)
    9. Small block of wood
    10. High quality paper towels (Bounty or above)
    11. An extra set of eyes to watch the #1 injection valve to determine timing
    12. Your 1/2" drive ratcheting torque wrench will make an excellent long
    ratchet for this job
    13. If you have an Ace Hardware Store in your area, by all means buy a 13 mm Ace Professional Gear Wrench combination ratchet. This tool is open-ended at one end and has a "ratcheting" (literally) box end at the other end. It is a very well-made tool, yet it is also very slim, particularly on the box end. Smooth, high quality finish.
    1. Assume cold engine
    2. Remove the #1 injection line. [Don't take anything off of the injection pump except the injector pipe. If you even __think__ of removing anything else (e.g., the nuts that hold the valves to the top of the pump body), you will regret it!]
    3. Jack up the front end and block it.
    4. Pump the hand pump several times to build pressure.
    5. With 27 mm socket and bar, turn the engine over at the crankshaft until you have gone through a compression stroke on #1 -- this will be noted by fuel coming out of the #1 open valve.
    6. Roll the corner of a paper towel into a pointed end.
    7. Twist and insert this into the #1 injection valve and remove all fuel.
    8. Note that you'll have to repeat this 2 - 3 times to get all fuel out.
    9. Turn the engine over by hand until you go through the exhaust stroke.
    10. Turn the engine until you get within 40 degrees of TDC (TDC = stub on crankshaft pulley).
    11. With your helper watching the injection valve closely, turn the crank as slow as possible by hand until the point where your helper first notices fuel "welling up" in the bottom of the injection valve. [It will be beneficial at this point to mark the "bottom" side of the pulley with chalk to inform you, underneath the car, that you are getting near the mark.
    12. Note the degree of advance at the timing marks on the crankshaft pulley. The correct timing should be BTDC 24 degrees +/- 1 degree.
    13. Advance is accomplished by swiveling the injection pump toward the engine at the top. Retard is the reverse.
    14. If your timing is within one degree of 24 degrees, you are finished. If not, continue.
    15. Pregnant pause. Still with me? -- then go to the next step.
    16. If your timing is not within specs, you must first loosen the nuts that hold the injection pump in place. There are four, and three can be accessed topside.

    17. Three of the nuts attach the IP to the engine toward the front (two topside and one below) and one is attached to a bracket at the rear (accessible topside). The Gear Wrench greatly, greatly simplifies loosening the pump.
    18. The factory workshop manual illustrates the need to "bend" a 13 mm boxed end wrench 45 degrees to the left for use in adjusting the timing. You do not need to do this with the Gear Wrench. [Please note that this tool is not a toy, by the way.]
    19. There are two ways to adjust the pump:
    a. the Jeweler's method and
    b. the Neanderthal method
    Both methods yield equally good results, both have their own inherent levels of risk, but they each require significantly different amounts of time. I prefer the Neanderthal method because my risk/benefit analysis suggests that this method is less risky to me, yet more fun. I will thus describe the Neanderthal method and, in parentheses (e.g., [ ]), will describe the Jeweler's method, where applicable.
    1. After loosening the four "holding" nuts, loosen (but do not remove) the remaining anti-vibration interconnections between the pipes. [Jeweler's method: remove all remaining injection pump lines.]
    2. Using your judiciously-placed prybar, advance by pushing toward the engine with the injection pump. If advancing is not applicable to your timing, push from between engine and injection pump to retard. For advancing on the 123 chassis (300D), the area immediately under the steering adjusting bolt provided an excellent "prybase", with contact on the injection pump provided by the small block of wood. Please be certain that you do not put pressure on the ALDA unit on the top of the injection pump. If unsure what is meant by the ALDA unit, re-read paragraph on assumptions and discontinue process. [Jeweler's method: Same procedure, but less force is needed because of all lines removed.]
    3. Please note that the movement of the injection pump with Neanderthal method is more difficult than Jeweler's method, since 4 of the lines are still attached. Why this method then, you might ask? Later, please. When moving the pump, it will seem as if the injection pump is not moving, but it is. The remaining lines are very stout and will be "springy" while adjusting -- look at them while adjusting, you'll see. Therefore, you need to hold the tension with the prybar and have someone tighten one of the front three mounting nuts for you to hold the new adjustment in place.
    4. Recheck the timing, by first repeating steps 4 - 9. Readjust if necessary.
    5. When the timing is complete, bend the #1 pipe so that the pipe attaches to the injector valve and injector with no force-fitting. It is critical that the line's nuts do not get cross-threaded. [Jeweler's method: rebend all remaining injection pump lines.)
    6. Reattach the anti-vibration interconnections. Be careful to not overtighten them. You have now successfully completed injection pump timing for the 617 engine.
    Contrasting the Neanderthal versus Jeweler's Method
    Quicker, more macho, more fun, much less danger of cross-threading. Injection pipes will "set" in new found position over time.

    Harder to move injection pump (4 lines remain). Potential threat of damaging injection pump (very minimal if prudent).


    Easier to move pump (all lines are removed), Injection pipes are already "set" when manually bent.

    Higher probability of cross-threading injection lines, less fun, messier (you have all 5 lines off spilling diesel fuel).
    Please let me know if you complete this procedure successfully; it took a while to type this, and I'd appreciate knowing when each person has completed the repair! Please e-mail me at

    Concluding Comments
    Thanks go to Jim Mahaffey, Dan Penoff, Stu Ritter, and Bob Sanigar for their posts. Thanks particularly go to Jim Mahaffey for providing DIYers an alternative for a procedure that normally requires special tools inaccessible to most DIYers, yet still provides an accurate and methodical method of injection pump timing.

    It should be noted that the Neanderthal method should not be associated with Jim Mahaffey in any way. For those of you who don't know, Jim is a "closet" "jeweler" -- having studied and repaired hundreds of Mercedes-Benz clocks and other electrical and electronic components over the years. As such, the Neanderthal method is a "technique" that any self-respecting "jeweler," even "closet" would probably find reprehensible. However, to paraphrase someone who shall remain nameless: . . . it (the Neanderthal method) is really the educated application of real brute force.

    Back to Jim Mahaffey: I don't think that it's a stretch to say that he is probably one of the most knowledgeable individuals in the world regarding Mercedes-Benz clocks.
    Jim's presentation at StarTech97 was a real treat for anyone in the audience.
    For more Mercedes-Benz links, please go to the following site:
    Mercedes-Benz Discussion List Home Page (
    To receive similar quality tips as described above on a daily basis, consider subscribing to the Mercedes-Benz Discussion List, which is located at the following site:


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