7.3 return line caps

Hey guys,

my 1994 frankenstein 7.3 N/A IDI is suddenly having severe air intrusion, the return line from the IP to the front right injector was half filled with air and it would not fire up. The shrader valve on the fuel filter head had next to zero pressure in it after cranking it over for a bit and as I watched the return line (mine are clear) good size bubbles were adding to the air pocket.

Seals were new viton orings as of almost 2 years ago.

Something I noticed is that the steel injector line nuts that thread on to the injectors dont even come close to contacting the return line caps and the return line caps are fairly loose. They wont pop off easily but they jostle around quite with my finger and when they do, air bubbles start to fill up the lines rather quickly. It seems to me that they could leak when cranking over the engine.

Is this really how these are designed? Has anyone tried putting a washer or spacer between the return line caps and the injector nuts to try and get the caps to seat better?

Lol. I cheat. Re use the old o rings above the new caps. Still put on the new o rings on the injectors and new caps, but I toss one of the old o rings on top of plastic cap before threading the injector line back on. Seems to work for me.

The nut isn't supposed to hit the cap.

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Hm, well I just went and pulled all the caps and O Rings out, cleaned everything, greased it all up with wolfs head bearing grease and put it all back together. Installed my new oil pressure gauge while I was in there.

The O rings on the rear driver side injector had a piece taken out of them, small but noticeable. Caps on the 3rd injector from the front on both sides do not "snap" into place at all, they just kind of slide on and off easily. Those O rings are fine, caps look OK internally. I really wish someone would make these caps with longer nipples on them, not only are the barbs too shallow, but they are so short that the lines barely hold on and the line clamps are wider than the entire nipple. Several line clamps were loose so I replaced them with injector clamps and torqued them down.

Looking to get a new kit from Wes currently.

I take a dull flat head screwdriver or a dull prybar and put the end on top of the return cap. Then, I'll bump the end of the handle with the palm of my hand to make sure that the cap is fully seated. Sometimes, they need this in order to fully seat.

A socket can be used to push the caps down. I wouldn't reuse O-rings even if they appear ok. The fuel return system is the weakness of the IDI. I believe the caps can get brittle after awhile but I have reused caps. Best insurance is a new kit with viton O-rings. Check inside of new caps for casting flash that can cut an o-ring. Even then a couple of years later problems can develop.

I am still using my old original caps. I agree, I would not re-use old o-rings. You can get new ones at tractor supply in the hydraulic section to tide you over. I say that because those o-rings are what I used and they worked well, but they did not last. They only lasted about 5 or 6 years, and then I started having minor leaks again, those hydraulic o-rings are Buna-N rubber. I did like everyone else and ordered some Viton o-rings from McMaster Carr, and they have been on there now about 3 years with no problems yet. I will see how long they last.

The fittings on the return caps do not have to be tight, they can move around. Like certain hydraulic fittings, like certain shop air fittings that move, the o-ring type seal can move and still keep a good seal.

Random thought. Has anyone ever tried 3D printing a cap? Lol

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79jasper said:

Random thought. Has anyone ever tried 3D printing a cap? Lol

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If I had a 3D printer, I'd give it a go...

I have access to one through my fabricator, we 3D print a lot of our fabricated parts to test fit before spending the money on expensive materials. Works great because You can just use cheap ABS plastic for the throwaway parts. But for something like the return line caps you need a heavy glass fiber reinforcing to help it handle the heat and petroleum, which increases the material cost for 3-D printing tremendously and makes it just not cost-effective.

But if you can do improvements like thicker walls, and longer nipples, more cost kind of equals out with better value.

At least with the 6.9 style I have found that plain old fuel hose works real well with the short barbs. The fit is tighter and I do not even use clamps. Most of the over the counter gates or dayco fuel line is diesel rated.

Another trick is to cut the hose 3/8" or so longer. Then rotate the natural curve of each line in the opposite direction of the next. curve toward valve cover, curve away from valve cover.

Selahdoor said:

But if you can do improvements like thicker walls, and longer nipples, more cost kind of equals out with better value.

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Would you be willing to pay $500-900 for a set with those improvements?

Thewespaul said:

Would you be willing to pay $500-900 for a set with those improvements?

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BAHAHAHA! No way!!