Hi all! New here, I am trying to get my 1975 300D back on the road after its winter hibernation. A little backstory on the car: I bought it last spring and got it running after 8-10 years of sitting. Changed the engine oil, transmission fluid and filter, both fuel filters and ran a can of LiquiMoly Diesel Purge through the fuel system. The car started hard when cold, and had the classic lumpy idle. In addition, it idles very low when cold, so much so that it will die unless I hold the throttle down a little for the first few minutes.

A couple of weeks ago I pulled the injectors out and pop tested them: only one out of the 5 had both a decent spray pattern and the correct opening pressure. I rebuilt them with new nozzles and set the opening pressure to 1650-1700psi. Yesterday I spent the better part of half an hour trying to bleed the fuel system and get the car running. When I finally succeeded the engine blew huge clouds of white smoke out the tailpipe for a few minutes and still idled really low. I took it for a 20 minute drive to try and evacuate the rest of the air in the system. Today the car wouldn't start again and bubbles came out the injector fittings when I cracked them while cranking the engine over.

Now for the questions:
Is there a better method for bleeding the fuel system? So far I have pumped the primer until stiff and then cracked the injector fittings while cranking until I get fuel coming out.

Which of the two fuel lines on the IP is the feed line? I suspect there is an air leak into the fuel system and would like to replace the feed line with some clear hose to check.

I have read mention of a rack damper bolt that often needs to be replaced, is this something I should look into?

Can someone point me to a good thread on adjusting the idle speed? From what I can tell the "proper" method is to adjust the governor inside the IP, but pulling the IP apart is not something I want to get into.

I have tested the glow system and it seems to still be working fine.

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Also meant to add, I have not yet adjusted the valves. That job was mean to happen this evening but without being able to pull the car inside out of the wind and rain I wasn’t about to pull the valve cover.

Did you do any hand rotation of the engine?

So, on the fuel supply lift pump there is 2 connections. The one that goes from the pump to the large fuel filter and on to the fuel injection pump is the pressure side of the fuel injection pump. The other side of the pump is the suction side.

The old-style hand primer with the shiny aluminum body and the hard plastic knob that is usually white is a notorious source of an air leak. If when you pump the hand primer it leaks fuel it needs to be replaced. The newest rubberized bosh hand primers are great.

All you have to do is push on it and a spring brings it back up for another push.

When you are using the hand primer when the air is out of the fuel supply system you will hear kind of a squishing or mild squeaking sound every time you push on the hand primer.

When people are testing for air leaks sometimes, they remove the fuel inlet hose and run it to another container with diesel fuel. That bypass everything to the rears of that.

The only faster method I know of to bleed the air out of the fuel supply system is to use an electric fuel pump. Put it on the suction side.

Either way you cannot get away from bleeding them at the injectors. Air trapped in those fuel injection hard lines compresses a lot and moves very little. A lot easier on your starter if you loosen all the Injector line nuts and let the trapped air out.

The fuel pressure relief/overflow valves (controls the fuel supply pressure inside of the fuel injection pump housing) typically have weak compressed springs and at low rpms don't hold pressure well at low rpms. Find a thread on stretching the spring.

Fuel supply/lift pumps occasionally need to be rebuilt and in particular there is a little 5mm O-ring inside that gets hard or sometimes falls apart.

If your idle speed is low adjust your idle seed to higher rpms. On mine 750-850 rpms is normal.

That is what I can think of offhand.

White smoke that smells like fuel is anatomized fuel particle that did not burn.

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84 300D, 82 Volvo 244Gl Diesel

Thanks for the input! I have not tried turning the engine over by hand, just on the starter. I drove the car about 400-500 miles last fall before winter hit, and it ran pretty well with the exception of the low, shaking idle.

I took a closer look at the fuel line connections on the IP, and based on what I remember of the OM617 in my old W460 and what you said above I think I've got a pretty good idea of the fuel flow path. Got some new fuel hose and some clear tubing, so will try pulling from a small fuel can and see what I get.

Being an early OM617, it has neither the early aluminum/white plastic primer nor the later black plastic one, but a mushroom shaped primer pump attached to the fuel filter housing. The primer seems to work well, but I might cap off the feed lines to the pump and filter housing and pull a vacuum on it to make sure.

I have a set of pencil style glow plugs and the associated timer and relay that I built a wiring harness for. Since the glow plugs will be replaced anyway I may go ahead and pull them to make it easier on the starter while I'm trying to bleed the air out of the injector lines. Once I can get the car running and can check for air in the fuel I will start trying to adjust the idle.

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Turns out the little rubber cap on the #5 injector return nipple was cracked, so that was probably part of the air leak. I temporarily replaced it with a vacuum cap since none of the parts stores locally even knew what I was trying to get. Did some searching here at Pelican Parts but came up empty handed as well.

You don't need it. Instead of the solid rubber cap some have a simple say 1 inch section of the return hose with a metal plug in one end. There is a special made metal plug that looks like a BB with a short stem on it.

Most people get something like a fine threaded machine screw that is slightly larger than the return line and coat the threads with some gasket sealant and shove it in. And they last longer compared to the solid rubber cap.

Places that sell the return hose that might be local.

A Mercedes dealer.

VW dealer because the same return hose was used on VW rabbits and likely on some smog systems in newer cars.

Volvo dealers because the Volvo diesels use to use the same type of Injector bodies. Sold in 1-meter lengths. The same hose may also be used on gasoline models.

NAPA (national auto parts)

Regular automotive vacuum line will work but might only last 2 weeks. Well enough for an on the road fix to get you home.

I have used a section of silicon vacuum hose between injectors, and it worked and sealed fine but within a year it got rock hard. It did not leak but lost all elasticity and I could not pull it off. I had to cut it off.

Somewhere there is a thread on the injector return lines and where to get them and part numbers of the VW return line.

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84 300D, 82 Volvo 244Gl Diesel

I replaced all the return lines when I installed the rebuilt injectors, but didn't have enough left over for a bit on the #5 injector, may have to get a little more for that. Good thought about the VW parts, I have a TDI in my Land Cruiser and have a spare set of injectors, will check those to see if the plug is the same.

getting air in the return line has no effect, it dumps back into the top of your fuel tank.

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1977 240D auto w/OM616.916 engine
2005 Matrix 5spd
2006 Prius

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Adjusted the valves today, most of them were very tight, a couple were in spec and one was a little loose. Still no luck getting the car to start, it sputters occasionally but never enough to fire off.

Trying to find a compression tester other than the cheap HF one I already have. It has never given me a reading above 300psi on other diesels, so I don't trust its accuracy. I feel like the compression is decent though, the engine stops spinning abruptly when shut off and there is not a lot of blow-by coming out the oil cap when the engine is hot.

Yesterday evening after dinner I decided to try starting the car once more. Pumped the primer 20-30 times, gave it a full glow, put the throttle about halfway down and it fired right up! Rough idle and lots of white smoke for a few minutes, then it smoothed out and ran great. With the valves adjusted it idles much smoother and quieter than before. Took the car on another 20 minute drive.

Today I tried to repeat the process: pump primer a bunch, full glow, half throttle. Nothing put the occasional sputter. I replaced the feed hose from the pre filter to the lift pump with a piece of clear hose and bled the system again. When I pump the primer I see no bubbles coming through the clear line, but still no start. Haven't found a decent compression tester, either.

Got the car to start again, no bubbles came through the clear line to the lift pump, so at least I don't have any leaks between the tank and the engine bay.

While the engine was running I noticed that the diesel puddled around the cylinder #1 pre chamber nut was bubbling slightly. Guessing that the pre chamber seal ring may be leaking and causing a loss of compression, which could explain some of the hard starting. I checked the other cylinders and didn't see any bubbles, but if one is bad should I plan to replace all 5? The injectors took a lot of torque (at least 100ft-lbs) to remove, so I am wondering if that could have slightly loosened the pre chamber nut and broken the seal.

just a thought, is the top of your IP dry where the lines go up to the injectors, or is it wet there?

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1977 240D auto w/OM616.916 engine
2005 Matrix 5spd
2006 Prius

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The top of the IP is dry. I should also note that the diesel puddled around the injectors is from bleeding the air out of the injector lines after installing the rebuilt injectors.

Cranking speed up to par? Slow cranking gets hard starting. Burned out glow plug or plugs, gets hard start and smoking, keep at it.

Little compression loss on pre-chamber seal,so little does not effect starting or running,
small amount of bubbling drive on.