The problem with my 1974 240D continues and my mechanic and I don't know where to look next for an answer. The fuel system seems to be leaking air. The mechanic can get the car running and it can be driven around all day stopping and restarting without problems. After sitting overnight it will not start. Looking at the prefilter, I can see that it is only about 3/4 full of fuel. Using the hand primer and bleeding at the main fuel filter doesn't seem to help. I don't see any air bubbles coming out of the filter connection but the prefilter doesn't fill up.

The mechanic put on a new lift pump, drained the fuel tank and checked the tank filter, blew out the fuel lines with compressed air, checked the prefilter and main filter.

The glow plugs are OK. I live in FL and the temperature was 70 degrees this morning so its not a cold weather problem. How long do you have to pump the primer pump to work air out of the system?

Does anyone have a fresh idea about what to do?

Did he fill the main filter with something that will combust before he screwed it on?

what is he doing to it?

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Jim

I believe it's normal for the prefilter to have a little bit of air trapped in it.... I think I would try loosening each injector line one at a time and see if air or fuel leaks out when you use the hand pump or turn it over.

Honestly, I don't know what he does. This morning I removed the main fuel filter and operated the primer pump. Fuel was pumping into the filter holder. I put the filter back in and bled the air out and tried to start. The engine would fire a couple of time but not enough to start.

It seems that not matter what I do, the clear plastic prefilter on the lift pump inlet is not full of fuel. Should it be full or is it OK to see some open space in this filter. Could the main filter be clogged and not be apparent? Should I take the main filter out and see if the car will start? Could the prefilter be cracked and leaking air? How long should I pump on the primer pump? I pump until I hear a clicking sound which I take to be the fuel valve in the injection pump opening.

it sounds like a fuel line leak to me. check the rubber parts of your fuel line under the hood and near the fuel tank. it also could be a rusty place in the steel line.

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.

Please describe the tests that were performed to verify this. If you don't know what tests the mechanic performed..........ask him specifically what he did and report back.

I tried opening each injector line at the injectors one at at time and operated the primer pump. Nothing came out, air or fuel, of any of the lines. Although, would I expect any flow with the primer pump or do I need to use the starter so that the injection pump turns? I don't have a helper at the moment.

I can find out on Monday when the shop is open. The glow plugs are the parallel wired Bosch duraterm type. I installed the kit about a year ago. Normally with the 70 degree temp as we have this morning, preheating is not required to start the car. I can start the car just by activating the starter as soon as I pull out the starting switch.

After activating the starter for a few seconds, the wires between the glow plugs feel warm which indicates to me that some current has flowed. Obviously, it doesn't tell me anything about individual glow plugs.

Have you replaced you primer pump? It might be leaking and letting air into the system.

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I had a '75 W115 300D that had leaking fuel delivery valves in the injection pump. It was very hard to start after siting overnight, but would run great once it built up it's prime. It would try to start, but since the lines were full of air it took forever. I replaced the o rings and copper washers at the delivery valves, and the problem went away. I think the parts cost was around ten dollars. Make sure you mark the delivery valve, so you get it back into the same spot as before. These cars are old now, and the seals are probably letting the fuel leak back into the pump.

In order to see fuel come out of the metal lines that go to the injectors, you need to spin the motor over with the starter. If you don't see a healthy stream, you might want to look at the delivery valves.

The lift pump and the primer pump were both been replaced in the very beginning of this problem. The car has been to the shop 3 times. Each time the mechanic reports the car running. I pick it up are do some start and stop driving that day. The next morning the car will not start.

Since the fuel to the injection pump exits the bottom of main fuel filter housing, if the housing is full of fuel, shouldn't the engine at least fire and try to run until that fuel is exhausted?

If you or the mechanic can confirm that you've got 12V to the plugs prior to the start, then, I agree, it's a fuel issue.

As mentioned above, the delivery valves are a likely culprit. The mechanic may be unfamiliar with changing these parts..........and the risk of failure is present if he doesn't know the proper torque procedure.

Good point, this no place for a ham fisted parts changer.

i have found that if i fill the fuel tank completely full,get a gallon in a proper container so you can top it off for the test,park the car on a grade with front end down,let set for the same time as it normally refuses to start,test to see if there are any changes in starting. now as i normally find a leak i have already got the area that contains fuel cleaned off(i use a steam generator). and in most cases with a small fuel leak the engine will fire right up because no air should enter the fuel system.
got to hunt and find any wet areas.
larry perkins lou ky

This is a long shot, but your symptoms sound EXACTLY like what happened to me.....I won't give you the gory details, but I ultimately had my car in the garage for a few days, rented a rental car to use for work etc. etc. Ultimately the whole debacle cost me $500, only to find that the car still had the same probem. I then fixed it for about a dollar!

This was the problem: the rubber hose that connects the hard fuel line from the fuel tank to the plastic pre-filter was old and cracked. Cracks formed on the inside where they could not easly be seen, not on the outer braided layer. Where the band clamp secures the hose to the prefilter, the cracks on the inside would distort allowing air too enter. I replaced the rubber hose with a new piece of Goodyear rubber fuel line from a local parts store, and all was well after that!

(Note: Your very first post EXACTLY describes what I did...drained the tank, checked the strainer, blew out the lines, etc........ You don't see any bubbles coming OUT of the connection at the pre-filter because air is DRAWN IN! You dont see any fuel leaking here because there is little pressure head here. But yet you still see air in the pre-filter, and the pre-filter never fills. Replace that hose and I believe you will be fine)

I hope this does the trick!


Good Luck,

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)