Hello everybody,

Sorry for the delay...some life-changing issues have come up and I needed to (and currently am) addressing them.

The fuel injector pump is installed, hard lines on, hard plastic line between top of fuel filter housing and side of pump replaced (sort-of a pain but it worked out. Autozone had a solid fuel line repair kit...boil end of tube in water for ten minutes, carefully press and twist onto barbed-end of banjo bolts, wait until cool --> tightly-sealed new (but black) fuel line).

I began this evening by replacing all the glow plugs with new that came in today (Beck/Arnley, made in Germany, couldn't get ahold of Beru or motorcraft, they all are confirmed glowing outside of the car).

With a squirt of starter fluid, I could get the car going (way easier than before with the plugs) and let it run high idle (the only way it WAS working...see below) for several minutes until engine was toasty.

I then decided that the hunting idle as I let my foot off the pedal is something to do with feedback in the vacuum lines and the vacuum shutoff that this pump employs...I couldn't help but think that it was literally acting like a surging lawn mower or tractor engine and that something blatant and obvious is causing an issue at this point. To test this theory...

I did some very cut and dry tests.
-I loosened the banjo bolt on the line between vacuum pump and intake housing (bolt on intake housing side) - no change. I then tightened this back up. This line runs in front above the fan and has a check valve in it near the intake.
-I then loosened the banjo bolt on the line between the vacuum shutoff and intake housing (again on the intake housing side) - car idle pegged and I didn't have to have my foot on the pedal. For the first time I could get out of the car and "poke around".

I then adjusted what I will call the idle adjustment screw (controls how "open" the butterfly valve is on the intake, mimics pedal press/idle speed cable offset adjust) to back the idle down (I had it up to compensate for the fact that the idle speed control in the car is currently broken), and it idled like a normal car...however, the position of the loosened bolt was VERY important and the car was VERY sensitive to this bolt being fully tight, fully loose, or somewhere in between...almost as if compensation/feedback from elsewhere (vacuum pump) wasn't occurring.

I have since come to a conclusion...the car is shutting off because the vacuum shutoff is being (apparently inadvertently) actuated. I have no idea whether the vacuum line between the pump and intake is clogged/check value isn't working, whether the vacuum pump needs rebuilt, or whether there is an issue with the vacuum shutoff mechanism itself, or the line between intake and vacuum shutoff. I don't think it's the vacuum shutoff because it seems to shut the car off just fine!

My intuition at this point tells me that, because loosening the banjo bolt on the line leading to the vacuum shutoff allows the car to run (keeps fuel going), the sum of the partial pressures between the vacuum line to IP, and to the vacuum pump, and the air housing portion of the systems, as well as the engine's vacuum itself in the intake, are all out of whack. I am just not sure what is the culprit here.

Suggestions welcome.

As far as IP timing, the car does run, and it does idle if everything regarding these lines at the intake are just so. There is white (?) coming out of the tail pipe. I say "?" because it's 29*F here and I think it's just moisture; it doesn't look like black or blue smoke at all. The most smoke is coming off the engine from diesel and oil dripping everywhere during work the past few weeks...so I think my timing is OK, which is faaaantastic.

Thoughts?

Many thanks to gmog220d for the extra drip tube!

See here for a few pics of work done so far

1976 mercedes benz 240d revival

Glad you got the fuel line in time and that it was helpful to you!

Just a quick reply here as I lack time to really get into it:

That thick "vacuum" line running from the intake to the back of the injection pump is not for fuel shut off. The IP is governed by that vacuum signal acting on a diaphragm in that rear IP housing. There's a throttle plate in the throttle body that creates a intake vacuum signal like a gas car would. At idle the vacuum is maxed and is pulling on that diaphragm to keep the engine at idle. Opening that line releases the vacuum and off the engine will go, as you discovered.

It's the so-called "pneumatically governed" IP. The 616.916 was the last Benz diesel to have that governor system, I believe, at least as far as passenger cars go. Fuel shut-off is accomplished by pushing that control knob on the dash forward to "STOP". There's a cable running from that knob to a lever on the side of the IP.

Dig for a link to the service manuals. They explain how to set all the control rods up, how to adjust idle, etc. If you can't find them let us know.

__________________
- Greg -
1973 220D, The Prodigal Benz
1974 240D

Good points, and yes. Glow plugs glowing brightly

Fantastic info. Much appreciated. Perhaps all that I need to do is confirm that the plunger "pulls" enough on the pump in the positions for stop, glow, and start. I have been forwarded a link to the FSM on a different forum and will be studying all related to the linkages, vacuums, and pump adjustments.

I'm really excited that it seems like I got this car 'revived' for the owner. She is really excited, too. Finally progress. I have spent countless hours with no intent on charging labor (this is a learning experience for me and it is nice that she lets me use her car for such purposes).

It's a great car - super cool to look at. Always looks on the road. I will keep everyone posted. Thanks all!!!

Some updates..!

About a week ago, I mentioned that one squirt of starter fluid (where air first enters the filter housing), and loosening the banjo bolt on the vacuum line from pump to intake (intake side), I could get the car to idle. This very important experiment proved a few things to me.

They are:
-#1. the pump, when the pneumatically-controlled governor is getting PROPER feedback, WILL supply the correct amount of fuel and the car WILL idle.
-->This tells me that the the pump is capable of accumulating the proper pressure to allow the injectors to fire. It also essentially eliminates the possibility of air sneaking into the fuel system by some other means, and validates the fact that I've bled the system properly. To individuals that do this stuff in their sleep, this is almost negligible...but to me, this is very important to know. As you may recall, on my original post, I had zero accurate information on this vehicle and I am not a mechanic...thank you for bearing with me. I am trying.
-#2. because of point #1, I now know that SOMETHING related to the vacuum line I speak of is getting TOO MUCH vacuum and preventing the engine from ever turning on, OR there is something else not right related to fuel delivery that is not right.

At this point, I am contemplating the following, given these pieces of information:
-is the reason that I can 'rig it' to idle by carefully adjusting the amount of vacuum manually with the banjo bolt a manifestation of the fact that the pump is out-of-time? There is also a lot of smoke, and it does not clear up, which implies that this may very well be the case. Further evidence is that it simply will not start (even with the vacuum line bolt loosened) when it is cold, even though the glow plug circuit has been carefully tested and is known to be functioning as it should be...but the moment it runs for a minute, it'll start right up as if the car was never broken in the first place.
-I have also been informed, though I can't remember whether it was this forum or pelican's forum, that if the pump is even two teeth out of time one way or another, it won't start cold. This further supports the theory that the pump is simply not correctly timed.

ALL OF THIS information leads me to believe that the shop working on the car could never get it to run right because of the exact same reason, except their issue was due to the fact that they trusted the splined pump gear (with missing tooth for timing) and the timing mark on the pump enclosure as the reference for setting the time...but after attempting to set the start of delivery with the drip method, I noticed that the drip occurred far away from these two original markings lining up, which suggests to me that either the pump was rebuilt and these markings were not observed, that the splined end was for whatever reason removed and replaced/shifted (although I think it is keyed, so maybe not shifted), or both...but I do not know.

So...my question is...

Could a diesel injection pump, hypothetically out-of-time, be the reason for a no-start when cold, and a reasonable (but smoky) idle when warm and with some vacuum feedback softened? Or, is this a simple matter of adjusting the governor (I have absolutely no idea where to start, except that I do see a bolt that appears to be an idle adjustment for the governor...if you have info I would much appreciate it)

In my mind this has to be what's going on - the smoke is due to uncombusted/partially-combusted diesel due to the wrong injection timing, and the no-start occurs at a time in which (cold engine) it matters the most to be spot on? Still, the glow plugs should cause the fuel to combust when cold and I should be able to warm the engine up this way until it idles smoky without the banjo bolt being loosened on the vacuum line...I would think.

The only other thing I can think of is that an adjustment of the governor itself is causing fuel shut-off far sooner than it should, or that the governor is malfunctioning...but I really find it hard to convince myself of this...again, any info would be great. The FSM only goes so far...

Anxious to hear your thoughts...and thank you.