That part of the system from the Fuel Supply Pump forward is supposed to be under pressure so it is hard to imagine how Air could be pulled into the Filter Housing if the Fuel Supply System is working normally.

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84 300D, 82 Volvo 244Gl Diesel

It's good to hear that the leaking crush washer at the filter wasn't leaking air into the system.

Wow, there are actually little filters in the injectors... I wonder if those ever get replaced or cleaned when the injectors are rebuilt.

My rebuilt injectors are pouring fuel out between the halves. I am not happy. It looks like they need to come out again.

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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles

They are not exactly Filters they are just narrow openings; there is no Screen or somethng like that inside; just 3 narrow passages. The Edge Filters are not supposed to come out.

You can clean them with Chemicals or an Ulatrsonic Cleaning Tank.

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84 300D, 82 Volvo 244Gl Diesel

It seldom works but it is sometimes possible hold the lower Nut with a Wrench and tighen up the upper Body with a Crows Foot type Wrench.

If you use a Torqe Wrench and you position the Crows Foot 90 degrees from the Head of the Wrench as in the picture the torque is accureate no matter the length.
you just need to be careful not to bend the Fuel Return Nipples on the Injector.

I don't now what method you used to rebuild the Injectors but except for not using a real Lapping Plate the below comes close to what a shop would to when they rebuild Injectors.
Vince Walden how to rebuild IDI Injectors.
http://vincewaldon.com/index.php?option=com_content&task=view&id=20&Itemid=28

I don't like the idea of using Abrasive Paper because I don't believe it is flat enough but People do it with no issues.

I think a Plate of Glass with 600 grit Lapping/Grinding Compound or finer is is better choice.

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84 300D, 82 Volvo 244Gl Diesel

I mailed the injectors to a shop in California and paid to have them rebuilt. When they came back and I installed them, fuel was leaking out of them. I also think that they were set at 115 bar instead of 135-143. I am having the shop that did the work refund the money and am taking them into the local Bosch shop. I don't have the equipment to rebuild them properly.

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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles

Often, injector half leaks are actually return nipple leaks dripping down. Injetor half leaks should have been caught during pop testing. I strongly suggest you rule out return nipple leaks first.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

The area under the return hoses was bone dry, but I could see fuel running out from between the halves. The person that rebuilt them said that he took them apart a few times to shim them and said they may have not been totally clean.

__________________
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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles