Theseus,

Did you remove the flattened crush washer from the large hollow bolt?
It looks like it might still be present in the last posted video.

__________________
78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Curious - Have you done everything that I have in this thread? Have you serviced the delivery valves and were any corroded?

__________________
Theseus

Instragram: doss_project
1984 300SD - 930 Blue, OM 617
Murfreesboro, TN

Theseus owned a ship in Greek mythology, and when a part of the ship needed replacing, it was replaced. Eventually, everything was replaced. Is it the same ship? (I own the car of Theseus. )

I have the 85 version. There is no crush washer present. Replaced the O-rings. No air that goes into the injection pump.

Banjo bolt, no stacked aluminum+copper washers.

__________________
Theseus

Instragram: doss_project
1984 300SD - 930 Blue, OM 617
Murfreesboro, TN

Theseus owned a ship in Greek mythology, and when a part of the ship needed replacing, it was replaced. Eventually, everything was replaced. Is it the same ship? (I own the car of Theseus. )

UPDATE:

Got a small tank to bypass the lines to the tank. Diesel flows easily in and out of the tank. However, no change in the performance ; engine same as before with air out from bypass banjo bolt.

I decided to pull a vacuum from the injector pump fuel supply line (after the lift pump). The vacuum allowed me to slowly pull diesel fuel from the bypass line. Small air bubbles came from the injector pump fuel supply line into the vacuum catch container. Was not a fast pull of fuel, but about an ounce in 3 minutes until you started seeing the bypass line fuel being pulled.

Only thing I can think next is to drain the injector pump of fuel, plug the bypass line and add compressed air to the fuel supply line. Then spray soapy water around the injector pump. That should reveal at least some location of the air leak. (I hope its not the o-rings of the valve body... )

__________________
Theseus

Instragram: doss_project
1984 300SD - 930 Blue, OM 617
Murfreesboro, TN

Theseus owned a ship in Greek mythology, and when a part of the ship needed replacing, it was replaced. Eventually, everything was replaced. Is it the same ship? (I own the car of Theseus. )

Yes, I've done everything in thread, twice at least, for three years now. Delivery valves did have some mild corrosion, I replaced with new from the dealer along with delivery valve springs & crush washers. I even sent my injection pump for a rebuild to a place Bosch North America recommended to me, D&W Diesel which was a nightmare. They were horrible to deal with and I don't believe they did a rebuild. Still had the original delivery valves... (DON'T USE D&W!)
Compression is very good 360 to 400+ Chasing this I even got a rebuilt head from Metric Motors, after pump rebuild and before new clear hard lines that showed the bubbles.

I don't have an air leak I can find, went over every inch. replaced all lines except undercar steel. I have exactly what your video shows, massive fine bubbles from pump when revved and an intermittent in intensity rough hot idle. No air seen before or entering lift pump

Guys, could it be the MW injection pump itself? Some kind of cavitation?

Exactly what I’ve been wondering.

__________________
1981 240D 4sp manual. Ivory White.

There seem to be five (?) topics on this forum addressing the same issue. So far, no one has found a fix to the exact problem; the banjo bolt fuel return is leaking air and there is no sign of air entering the injector pump.

I think we can solve this!

1. Bosch injector pump service manuals have a section on plugging the fuel bypass and all ports. To check for air bubbles, it must be pressurized, then placed in an oil bath. This should show you if there is an opening outside. It is possible, however, that an o-ring could be faulty somewhere on the delivery valve body holder.

2. When I prime the banjo bolt, I can see air coming out. Air comes out, but not as much as when revving it. Despite my best efforts, I do not get the banjo bolt "squeal." I think I should get it. Over time it does encounter some resistance, not all of the air is expelled, but some of it. I can keep that going with air coming out the bypass. Mind you, no air is coming from the supply.

4. There is a possibility that the air is coming from negative pressure. What processes would cause that, and where are the possible points of air entry?

5. Cavitation? It might be possible. Is cavitation a dynamic phenomenon? It is my understanding that bubbles grow and then collapse. I see air bubbles without flow.

__________________
Theseus

Instragram: doss_project
1984 300SD - 930 Blue, OM 617
Murfreesboro, TN

Theseus owned a ship in Greek mythology, and when a part of the ship needed replacing, it was replaced. Eventually, everything was replaced. Is it the same ship? (I own the car of Theseus. )

4) Damaged barbs, ill-fitting test hoses, defective crush washer for cap screw of IP pressure relief valve??

__________________
78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

UPDATE:

- rebuilt lift pump (some components looked worn, now my bypass valve can "squeel". No air comes out during priming
- Double checked and retightened the fuel inlet to injector pump. Wiped dry, confirmed no fuel leak. No air entering at all.
- Replaced the injector return lines with clear tubing. Vacuumed all air out, confirmed no blocakge. Upon startup, noticed small air bubbles from all lines to evntually put air bubbles over each return line loop.
- Filled the auxilliary by tank full (to bypass the fuel tank) . Eliminated any possibility of air coming into the primary fuel filter
- diesel purge, basically clean output. No difference during purge.
- wiped clean injector pump and all areas near it. No fuel leaks, no oil leaks.
- pressurized the injector pump with air, 80 PSI. Sprayed soapy water all around, no indication of air leaks. (Is is possible air could be netering from the injector barrel housing though one of the o-rings?)
- Fuel filter o-rings double checked.
- Revved the engine. Still have some air the comes from the bypass return, but not nearly as much as it did before. So air is coming from somewhere in the injection pump.
- Engine still has shaky idle.

I've been checking this thoroughly!

Recorded the injectors and injector pump sound with a mechanic's stethescope. It's hard to say what noise is considered "normal". Injector #5 is pinging and sounds different at the injector pump and injector.

Video on the sound of injectors and injection pump.
https://youtu.be/v2jWoysBFuE



Next to check:

- Valve clearance
- Chain stretch
- Injector Pump Timing (possibility of drip test)

__________________
Theseus

Instragram: doss_project
1984 300SD - 930 Blue, OM 617
Murfreesboro, TN

Theseus owned a ship in Greek mythology, and when a part of the ship needed replacing, it was replaced. Eventually, everything was replaced. Is it the same ship? (I own the car of Theseus. )

Update:

I checked valve clearances and adjusted them to specification. Fired it up and there was no difference.

The PO informed me that the millivolt glow plug test indicated cylinder #5 was outlier, which coincided with audible nailing I heard near that cylinder.

While running the engine, loosened (cracked open) #5 injection hard line at the injector pump. As expected, shaking increased; however, the nailing noise vanished! This has encouraged me to spend some more time investigating #5.

None of the other lines removed the nailing as well as #5.

Hi,
I've chasing this issue off and on over the years on my '83 300D Turbo.
I've done all the things you've mentioned with no change.

However, I did eventually bypass the send and return metal fuel lines under the car by running two 5/16" rubber fuel lines and 'zipping' them to the body to hold them.

This has made a big difference in my car.

I imagine if you look closely at those metal lines going to/from the tank you'll see some of the metal flange mounts that hold the lines to the body are leaking fuel.

These leaks are bound to happen on vehicles with high mileage.

Most of my mounts were leaking on both send and return lines so it made a big improvement on my idle and the amount of air I saw in the return circuit.

Just my .02 .... .

-Chris

Thanks Chris!

Leaks are probably happening in my fuel lines as the bypass to the tank did help little. However, I can see no bubbles entering the injection pump. There are some theories as to why the air could be coming out of the return and injector. I read that there could be a faulty delivery valve and thus combustion products could be the "air" I am seeing coming out of the banjo bolt fuel return. Solution would be to fix delivery valves, with #5 being prime suspect. Delivery valve 1 and 2 were in bad shaped and would be investigated too as well. Perhaps using the lapping compound trick. Another point could be the injector barrel oring or a Crack in the injection pump. However, I would be seeing fuel coming out.

Anyway, I came up with the nuclear option. I found what looks like a good injection pump from a 1985 om617a at a salvage yard for less than some seals and repair components would cost to diagnose this. I am going to run a leak down on all cylinders, once that passes, I'll install the injection pump. I need to replace the oil filter gasket anyways.

__________________
Theseus

Instragram: doss_project
1984 300SD - 930 Blue, OM 617
Murfreesboro, TN

Theseus owned a ship in Greek mythology, and when a part of the ship needed replacing, it was replaced. Eventually, everything was replaced. Is it the same ship? (I own the car of Theseus. )

Please update as you progress.
The injection pump is perhaps the least understood component on these cars.

__________________
1981 240D 4sp manual. Ivory White.

Delivery valves if worn must be changed. nothing you can do about it.
Search my 2011/12 posts,... 8 years of nightmare's, ended selling car.

dont buy used IP if not tested on running car.


cheers

ChO

.

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w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded
next wish/project: w114 coupe OM603 powered

Any updates on your progress? I'm having a similar issue as well.

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Garage:
1983 300TD
1985 300D
1993 190E 2.6

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