It's popping at the quick coupler? That HF kit is not very good. The fittings are nickel plated brass (should be steel for such application) and tolerance is lousy. I did extensive work to my HF kit to make it work and leak free.

Post a pic of your injectors. Where is the oil coming from?

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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

Yep it's popping off at the quick coupler. It is a different quick coupler than the one used for the glow plugs, so I'm guessing it is the quick coupler that is causing the problem. I definitely have it fastened as solidly as it will go ... I tried several times, but each time it would pop off. I think maybe I could rent a tester from Pep Boys and see if it works any better.
Injector pics ... the oil was all over the tips. Some of it was fuel (those droplets on the cardboard were partly fuel that dripped out):

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

There is only one quick coupler (the brass thing at the hose with a spring loaded collar). The part that goes on the injector adapter is a fitting. Check the shape of that fitting compared to the ones for the glow plugs to see if it is different. Also check the quick coupler o-ring to make sure it has not unseated itself. If it has, lube it with some oil then pop it back in. Also lube the collar with light oil to make it work smoother.

There shouldn't be oil on injectors in a good running engine. What you have maybe fuel from your compression test with the fuel not shut off completely + soot which together look like oil. One way to find out is put the injectors back in, run the engine till fully hot and take the injectors out. They should be dry with just a thin layer of soot.

While your injectors are out, might as well get them pop tested for opening pressure and spray pattern and correct it if there are problems before putting them back in. Don't forget new sealing washers (heat shields) every time an injector is R&R'ed. You gotta plan what to do when pulling injectors and do as much as possible and not use up too many sets of heat shields which add up and gets expensive.

__________________
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

It could be bye bye tester if you get ignition but that depends on the state of the engine and the tester - don't the really good testers have a pressure relief valve? Anyway according to the SAE OM617 development paper at idle the cylinder pressure is just under 40 bar - that's about 580 psi.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

I just used a Mighty-Mite type vacuum pump on the stop valve. Just a few pumps is enough (~10" vacuum?). That lets you test the stop valve at the same time.

I also have the Harbor Freight Diesel Compression set (~$20), and it works fine. You probably aren't latching the coupler right. It is just a standard air-tool quick-connect. Insure you push it in fully and pull the collar forward, if the spring doesn't.