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Marty, Technician
Category: Classic Car
Satisfied Customers: 53904
Experience:  Automotive technician with 34 years experience repairing all makes and models.
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To Mr. Marty: I have a 1974 Mercedes 240D automatic that I

Customer Question

To Mr. Marty: I have a 1974 Mercedes 240D automatic that I can not get fuel through the injector lines. It has been sitting in an estate for some time now. But prior my Dad had seen it advertised, went to look at it and found it running when he got there, he drove it and purchased it, came home parked it and it would not start the next day. Tried at the time to restart it, but it would not. The body is straight and it shows only 46314 miles, I thought it might make a good run about car. I have been trying to bleed the system, and seem to have fuel to the pump. the owners manual is not very helpful, it did not even say to drain and refill the pump body with oil as scheduled maintenance , the oil was diluted, black,but about a cup of oil came out of the pump. So far I have checked the manual delivery pump (Black-Bosch-newer smooth barrel-no lock down) Pump till check valve rattle, pulled return "cigar" hose off, spun engine and got pulses of fuel. I held my finger over the return on the filter after banjo tee, pumped by hand, holds back pressure, no bubbles. I opened the air bleeder on top of the pump (between #4 injector outlet and red oil fill cap on pump), again no air, just fuel. Then took the vacuum line loose at the intake manifold, spun the engine, and had a pulse from it but not much for suction. Then took the air governor line loose below the butterfly and all that seemed to be open. Loosened the injector line nuts at the injectors, but no fuel has dribbled out. Have recharged the battery 3 times trying to prime the system spinning over only 30 seconds at a time max. The combo fuel shut off/run/glow/ starter pull knob seem to cycle and function OK. Even clicked the seat belts in case there is a safety no start system. Looks like the glows are working also, they had a little seepage of fuel on them from the small "leak back" hoses on the injectors from trying to pressurize the system and it evaporated off the buss bars between the large glow plugs. The pump is very hard to get to. Even removing the battery and washer tank,it leaves the filter, power steering reservoir and assorted lines in the way. I am hoping it is something simple that I have missed to easily prime the injectors. I do not want to pull the pump,test it and reinstall it. The nearest MB dealership is 2 hours away. After looking at the schematics you sent to JACUSTOMER 4 years ago about a stationary engine/buttery fly conversion. I think this one is a engine 615,616M injector pump with pneumatic advance ( since can not see far enough down the pump to read the numbers, but do see the red oil fill screw cap) engine does not spin real fast like the newer gear reduction starters, but that should not make a difference on the fuel priming. I am also trying to figure out what to do with a 560SL/1987 convertible that is damaged on the drivers side. It only has 69K miles, but oddly had written on the air cleaner 475HP, yet no other badges showing up grades,
Thanks for your help. Mark
Submitted: 1 year ago.
Category: Classic Car
Expert:  Marty replied 1 year ago.

Hi, bleeding the air from the diesel injection pump can be very difficult on this model. The best way to handle this is to start the car using a starting spray such as WD40 or silicone. Have a helper crank the motor while you spray into the air intake. You need to run the motor on the spray until the air bleeds from the pump and runs on it's own. I usually hold the throttle open and run the motor on the spray at about 2000 rpm while bleeding the air from the system. If the car has a manual transmission you can tow start the car.

Let me know if you have any questions.


Customer: replied 1 year ago.
thank you for the response. Yes we tried the WD-40, even found the older type can that still would still atomize the spray. Then tried some brake clean as a last shot, but didn't fire. Avoided using the glow plugs because fuel is ingested instead of timed injected, and didn't want per-ignition. Have avoided ether to this point again because of the glows. Do you think glows and WD would be OK? (Its an auto trans) Thank you, Mark
Expert:  Marty replied 1 year ago.

Hi Mark, I found that spray silicone works best. Go ahead and glow it and see if it attempts to fire. I would not use ether. Also make sure that you are getting voltage to all of the glow plugs. Are the bus bars between the plugs getting hot when you glow it?

Customer: replied 1 year ago.
Will try the silicone spray and glow plugs later today when a helper is available, and the diesel fuel smoked off the buss bars before when I had seepage from " leak back " small lines interconnecting /leapfrogging between injectors while holding back pressure. Some diesels will not push air out of injectors without "cracking" the nut at the injector itself. Would that make a difference on air lock bounce back? I have a 4-390 Consolidated diesel that requires that, or you could crank all day to no avail.
Expert:  Marty replied 1 year ago.

I always leave the nuts loose on the injectors when using the silicone spray and then I close the nuts as soon as I see fuel oozing out.

Customer: replied 1 year ago.
Tried the silicone spray (NAPA-MACs brand and GUNK brand) and sprayed some on the Z bar busses and they both smoked.But never hit once. Reglowed several times, sprayed at different rates and throttle at all positions. Let the glows cool for a bit and finally tried some ether, but again not a pop, much less priming the injectors. Battery starting to lose some umph, but tried holding hand over intake, and there seems to be suction, just not a lot, but again maybe spin speed. If I hadnt seen it drive in,I would have wondered if it could. Unless both the brake and throttle pads replaced, shows little wear. Did not spin over like free wheeling/lack of compression, and not lumpy like cam locked. No odd noises when spinning coming from the front drive train, but could something there be a base cause of both? But pump needs to turn in order pump the fuel cam, and it was pulsing fuel out the return line. Had a mechanic help for about a 1/2 hr, but he was puzzled also.
Expert:  Marty replied 1 year ago.

It sounds like there may not be enough compression. You should probably do a valve adjustment and run a compression test. Are you spraying a steady spray of silicone into the intake while your helper cranks the motor?

Customer: replied 1 year ago.
run lite to heavy amounts of both silicone and WD-40 to the point it was coming out the intake.But not to the point of hydraulic locking the cylinders. When cranking, it didnt act like freewheeling past one or two dead cylinders. Why not even one hole fired not even once has me puzzled, since it had ran, and it didnt run out of fuel prior. Since it had not run out of fuel, I not sure how air could be in pump.Thank you for the good advice,its just this is a real head scratcher . Will be out for the day to go skid out some fire wood with the cat,and still trying to get the 41 buick and other estate cars ready to sell. Will look at my diesel compression tester to see if it will will interchange with MB, but time is kind of a premium here on the farm.
Expert:  Marty replied 1 year ago.

Let me know what you find out. The diesel is all about the compression. If you have compression and glow plugs you should be able to run it on silicone spray. If it won't even fire I'd have to suspect it has lost compression. You might try removing the injectors and squirting about 6-8 squirts of oil into each hole and letting it sit overnight then try it again.

Customer: replied 1 year ago.
Have a compression test set for Cummins 2.9l-3.9l-5.9l and 6 bt 4.02 bore also for the v-185 threw vt555 injectors. last one is the 5.5 bore engines (855) also 903 v8. Will any of these fit the 240D engine? Wont removing the injectors affect the carbon dam and carbon remover tool for the seats? Would thinning some STP with an evaporating base, spray in while cranking (W/O glows), let sit and thicken to test ring seals?
Customer: replied 1 year ago.
Will the z-buss bar still go hot if the glow are toast?
Expert:  Marty replied 1 year ago.

I'm not sure about the compression testers. You will just have to check the adapters and see if they will thread in. I would not try spraying the STP into the motor. The buss bars will not get hot if the glow plugs are bad.