PeachParts Mercedes-Benz Forum - 617 fails to hold idle on the stop.........no oil pressure

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617 fails to hold idle on the stop.........no oil pressure

i have a 1975 300d i live in alvin i know its a fuel problem i joined your group post a all filters have been changed all air out of system starts and runs for a min or so than dies like running out of fuel can do the primer thing again and it will start Does this thing have a fuel pump or does it use the vacume pump for that, the friends we bought it from said they where driving back from fla. and it died they dont know anything about cars please help in the past this car has had a new head/new inj pump/new water pump/all new injectors/when it starts it runs great but will only run for a min or so Thanks for the help:confused:

Take the fuel shutoff valve fitting off of the injector pump it should be a brown vacuum tube with a blue stripe coming from the firewall to the side of the injector pump disconnect it and see if it runs.

It might be picking up air somewhere. Are all the fittings tight?

Sounds like your fuel hand pump is letting air into the system. See how much air is in the plastic prefilter then start the car and let it die, then see if there is more air in the filter. If there is more you probably need a new hand pump.

Quote:

Originally Posted by Joyce (Post 1400117)

#5 above sounds very logical. If it's not that you might check to see if there's a loose fitting on the suction side, in other words, between the tank and the mechanical fuel pump. If there's a pin-hole or loose or cracked fitting anywhere along there, it would suck in air and airlock.
Another possibility is that there might be something wrong with the mechanical fuel pump. Engine runs okay when primed with the hand pump, but then stops when the mech. pump won't keep up.
I've never seen that problem, but one way to eliminate the possibility would be to start the engine, and then work the hand pump to keep pressure on the injec. pump while the engine is running. If the engine doesn't stall out as before, you'll know more than you did when you started.

Wouldn't it make sense too that he might be experiencing a bad lift pump possibly? He could tell that easily by priming and starting, then watching the prefilter to check for pulsations. No pulsations could be dead lift pump.

Where is the pump is it next to the oil filter ?? This is not a TD its a 300D this is our 2nd 75 300D any time we have had problems its always been fuel somtimes just a small line leak cant find leaks any place this was being drivemn on the hwy from FL. it ran fine than started to loose power and die now after priming it only runs about a min it will try to restart but if it dones runs 5 sec or so if you go through the air bleed again even bleeding at the pump it will run again any where from 1 to 5 min than die all the filters are new the tank has been cleaned and strainer cleaned ( biggest allen wrench i ever seen ) Any way i dont remember seeing any air bubbles in the clear filter however when you pump the primer you can see it move fuel when you push down ,and when you let it up looks like it sucking back and mabe a little foamy when this happend on the first one we had it ended up being a $1.00 piece of hose

Loosen the fuel filler cap just to establish the tank is not vacuum locked. If the tank vent is obstructed they can do these type of things. You could also consider putting a line pressure gauge on to see if that lift pump is history after that. I would gravity feed it from a container to make sure the test is absolute. It does sound like you know about air leaks already. The foaming you see in the pre filter could be air introduced by a leaky primer pump or just agitated diesel fuel possibly.

Try an alternative fuel source. Get a one litre pop bottle. Run clear vinyl hose, the same size as fuel hose into the bottle. (you can buy the hose at most hardware stores.) Hook one hose up the inlet of the clear fuel filter and hook the other up in place of the return hose on top of the large fuel filter. Start the engine. This will tell you three things. 1. It will tell you if the fuel lift pump is working. If the fuel circulates thru the pop bottle, the lift pump is working. 2. If it runs ok this way, the problem is in the lines or fuel tank. 3. If you see a lot of air in the circulating fuel, you're probably sucking air thru the primer pump.
It's a simple, inexpensive test that can help you narrow the problem down significantly.

I am by far an expert at this engine, It seems as though something at the idle setting is wrong. If the fuel pump were going south, i don't think it would run at all. On later models there is a pin on the injection pump that requires attention. I suggest a search something along the lines of rack pin, injection pump, and see what you come up with. It appears from your description that the mechanics of combustion are ok, but you are not getting enough fuel at idle. Someone with more experience than I should chime in.
Good Luck.

617 fails to hold idle on the stop.........no oil pressure

hello 1975 300d will start now will only idle for a min or so if you run it faster than idle it will keep running ,but if you return to idle it will soon die and you will need to pump on primer bulb again when its going to die there is NO bubbles in the clear filter but no real flow to be seen the fuel tank screen was cleaned and all filters changed it seams to run longer if you pump the primer when the engine is running it will keep running at about 1000 or so again no bubbles does this thing have a fuel pump and if its week would it pump enough at a faster engine speed to keep it running also it shows no oil pressure the oil has been changed the valves dont clatter it has a manuel guage we took it loose from the oil filter base and blew a little air in the guage moves fine is there a bypass in the oil pump i need to clean also you can remove the oil filler cap and see lots of freash oil on top Thanks for the help

Try raising the idle. The adjustment on the newer engines is a tall screw with a slot head between the engine and injection pump. There is a lock nut that will need to be loosened before you adjust the screw and tightened back down when you get it set to the correct point. Keep tightening the screw until the car idles better.

Not sure about the oil pressure but don't run it much until you figgure that out. :eek:

I believe the 75 has an idle knob on the dash. Make sure it's turned all the way counterclockwise.

Not to be an @ss, but using a period every now and then makes things MUCH less painful to read. A more detailed title also helps. Something like "No oil pressure and will not idle."