Hello. My name is Dave Roberson. I own a small shop in Mesa Az. One of my customers gave me an 1981 240D. Auto Trans. It is a no start. Here is what I have done before trying to start.

Drain fuel tank..replace hoses and blow out lines.
New Primer pump..new fuel filter..new fuel hoses in engine compartment.
New Battery and 00 Cables made.
Remove injectors..clean and do a pop test on my bench tester.
Check glow plugs..glowing brightly..check compression...LOW 180 to 280.

Now the problem..I have good fuel flow to the injection pump with no air. I have cranked and bleed the injector lines.(seems to have little pressure but some) Very little fuel is comming out of the injection pump. Not enough to pop the injectors (make them spray).

How do I check the injection pump?? The vac hose to the fuel shut off is disconnected.

Is their an common problem that I am not aware of due to my lack of product knowledge on this car??

Thanks in advance for your help. Dave

The injection pump does not put out much volumn. After the lines are full it just takes a bump to pop the injector.

If it is not starting my first suspect would be the glow plugs.

If in doubt about the fuel system you can take off the air cleaner and spray wd 40 into the intake. If you have compresssion and glow plug function it will run fine on the wd 40 as long as you keep spraying it. I use this trick when I have interupted the fuel and need to prime the system comprehensively.

If you get the fuel sysetm going good and you cannot get the glow plugs working for some reason you can pull start it. This is easy if a stick a little more complex but not bad if an automatic.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I would take the lines off @ the injectors and make sure you are getting fuel to all 4 injectors. If you are, then the above method should get it started..
DO NOT use ether. As tempting as it may be, it will cause damage.

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81 Mercedes 300SD 289k.......SOLD
82 Mercedes 300CD 252k......slow ride

82 mercedes 300 SD...mi Unknown
83 Mercedes 300D ????ksniff..gone too
84 Mercedes 300D 148k........SOLD
85 Mercedes 300TD 386k and holding some one elses project

Ok It is an Auto Trans . Glow Plugs working. I verified this with a visual with injectors out and before that checking amperage draw on each one.

I am getting fuel to all injectors. As I found out when I bled them. The injectors are not opening when cranking with a good battery. I tested this by hooking up an injector to an injector line outside of the cyl head and cranked it.

The injection pump is not supplying enough volume or pressure to the injectors.

I am asking if anyone knows how (or where to find out how) the fuel supply works inside of the injection pump. I will ask a few Mercedes Techs tomorrow and if I do not find out I will get a used one and dissassemble it and figure it out.

Thanks,Dave

Do you know the history of the car? When was it last run? Does the owner know what happened to make it not start or did he buy it that way?

Did you change the secondary fuel filter as well as the primary?
The secondary looks like a small oil filter near the injection pump.

Does the '81 240D have an oil reservoir on the injection pump? If so make sure that it is filled. I am not sure if this year has the pump lubricated from inside the engine or not.

Next I would disconnect the line from the lift pump (fuel pump) to the injection pump and make sure that it is pulling up enough fuel.

I would also try this, disconnect both rubber fuel lines from the long metal lines going back to the tank and insert them into a jug in which you have poured two cans of Diesel Purge. I would then pull the remove the injectors from the head but reconnect them to both the hard and soft lines. Then crank the starter until you have run through most of the DP. This might loosen up the internals of the injection pump. Plus you will be able to see if the injectors start popping.

I would also pour Marvel Mystery Oil into the cylinders to see if that helps with the compression. If the car has sat for a long time the rings could be rusted and stuck. I had to do the MMO treatment a few times before my engine regained its compression. Let it sit with the oil overnight.


Since you are on the forum, try some searches using google advanced search. Put mercedesshop.com in the domain box and look at Diesel Purge, Injection Pump, Pull start. etc


Good luck

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"I have no convictions ... I blow with the wind, and the prevailing wind happens to be from Vichy"

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Regarding the low compression, have you checked the valves yet? They do tend to tighten up on these engines and the are supposed to be adjusted every 15K miles.

Disconnect the fuel return on the pump and see if anything is coming out. If there is and the pump will not open the injectors it sounds like the pump might be bad. Perhaps the pistons in the pump are stuck at the top of their bores.
A few times they have been stuck in past threads. I think the members pushed them down a few times until they activated again. Those cars had been sitting a long time.
You can also remove the lines from the pump it should squirt fuel oil out each port.

Stubborn starters like the 240D AUTOMATIC can be tow started. Get them up to about 35mph for a minute or so, turn the key ON and put shift selector into "S". The engine will motor through.

ALSO, DO check the valve clearance. The intakes tighten.

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.

Valve clearence and Valve timing checked....

Fuel flow verified right at injection pump after lift pump. Lotsaflow

Thanks Berry..I will check fuel return flow out of injection pump. I can now see how a stuck open return valve (called overflow valve on my 95 Cummin's) would cause low to no pressure in the injection pump with a bad valve stuck open or even partially open.

Marvel will be the next step after I get her running. I know that his car may not be worth the effort. I am a tech with 30 or so years experence with German gas cars. I can not give up...I must not just get it running (not really importaint) but I MUST know why. Personal problem I know.

Car has not run in 2 or 3 years. Customer said one day it ran and the next morning it did not. Since I could not get it running for $100 he gave it to me. I will probally donate it to a high school auto shop once I get it running.
Thanks Dave