Hi Folks
i just want to ask a tiny silly question

I have a 1991 190 2.5 with the legendary OM602 NA engine

is it normal for the diesel injector return end cap to fail after 3-5 months of use ?
because i m tired of replacing it too often and the mess i have now diesel fuel all over the place . i even made i custom one myself with i heavy duty braided return hose and pluged it with a screw and it work fin for a wile but it fails last day after 4 months
i know the end cap are very cheap but failing too fast like that makes me worried because a friend also have a 1992 190D 2.5 NA om602 he bought it 2 years ago and he never changed that cap ever

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1991 190D 2.5 515K

use a sheet metal screw.

I see you are using web reinforced hose, is it the "good kind"? I mean of the right size and not from Pep Boys or something
Also check the barbs on the injector return nipple to be sure they are in good shape.

I used a machine screw on my 671 on the reinforced hose some 10 years ago and its still holding fine
The original rubber cap the factory used blew out on a trip and I spewed diesel all over the car behind me before I realized what was happening and I had to pull over and fix it..

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Proper size, sold here, push on by hand and then a final push with needle nose works for me. I also thought that the return runs through the secondary filter. Never heard of pressure from a clogged secondary causing a problem but if due for a change anyway can't hurt, and cheaper than two gallons of fuel.

I have not read of anyone reporting this issue before. And you did not mention any issues like an uneven idle.

Are any of the hoses in the return kinked even partially?

I have read of the interior of brake lines deteriorating and blocking off flow but never the return lines. As mentioned with the little nipples on the Injectors maybe there is one of the nipples the return line goes on that is nicked/scratched or even partially blocked off

You could get a longer hose to test (connect it to the fuel return) and fill a jar 1/2 with diesel fuel and submerge and see if there is bubbles coming out of the return.

This sounds bizarre but if 2 parts of your Injector Nozzles are not seating well it allows combustion gasses to pass into the Injector body when the fuel is not being injected (and to a lesser extent air from compression). Somewhat like having a bad valve in your cylinder head. Combustion gasses can get by a bad valve seating area.

This does not fit your particular issue but other people read these threads. Swapping the position of the Injector to see if the leak is still on the same injector could be revealing.While I was writing the above I forgot about this. The little return nipples are pressed onto the Injector Body and swedged/crimped over to seal them tight. However, once in a while those nipples become loose and it is not the hose that is leaking but around the nipple. Putting a scratch near that possible leaking nipple so you can identify it and swapping the position of the injectors to see of the leak follows the same injector would be an indication that the leaking nipple is either loose or has some other issue.

The normal fix for the nipple issue is to replace the upper Injector Body but be aware that doing that changes the pop/opening pressure.

One of our members solved the issue of a loose return nipple buy cutting it off and welding over the hole and he always kept that Injector at the rear.

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84 300D, 82 Volvo 244Gl Diesel

I use oem blank off plug. Never failed on me.





The right under one is the blank plug.

A 604 070 02 55

On my '81 300SD I have also the factory one. It is original and has never failed. Seems to me that you must really have a lot of pressure, abnormal pressure, pushing it off the nipple.

Replace all the return hoses as well as the end plug. An aging hose can swell shut, increasing return pressure. Also use proper braided line. The braid is there to help the hose grip the barb.

thank you all for your help i think maybe i need to replace all return hoses because i never done that in my 5 years ownership
my car idle rough for about 5 seconds in morning when cold but after that it runs great so i don't think that problem has anything to do with the end cap because the rough idle just showed up recently and i have that end cap problem in my entire 5 years of ownership i even thought that's normal

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1991 190D 2.5 515K

Yes, go to Harbor Freight and buy a nice pair of duck bill pliers and some good dykes, buy the correct return hose from the host (2X as much as you think you'll need !) and replace all if it, the front bit from engine to filter is longer than you expect and should go through a support or zip tie .

The duck bill pliers make it easy to grasp, twist and remove / replace the hoses, the proper, slightly more expen$ive hose will last longer too and any left over will come in handy .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better