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Chasing air leaks

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Jon Sherrod, Sep 16, 2020.

  1. Jon Sherrod

    Jon Sherrod Registered User

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    I have a 1990 F250 with the 7.3 IDI with at least 300,000 miles on it. The truck has spent several years with little usage and no maintenance. When I got it, it would run, but ran very rough. After some internet research, I learned it was probably due to air in the fuel system. I bled the fuel filter and it helped tremendously, but did not solve all of it. I then started to fix some stuff. I replaced the fuel filter with a one piece WIX filter with water sensor port. I also replaced the return system cups, orings and fuel lines. I replaced the fuel line from the filter housing to the injector pump. I also replaced the fuel line on the back side of the motor that connects the fuel return system to the return line going back to towards the tank. Today I replaced the one-way valve that connects the filter housing to the fuel return system. Today I also replaced the fuel filter vacuum sensor because I noticed it was leaking. After bleeding the fuel filter again after replacing these, it seems to be running much better although I believe the engine is still missing bad on one cylinder. (This is probably another issue for another day. I think I have an injector laying out. I got the truck from my dad, who purchased it used and put about 200,000 miles on it. He has never serviced the injectors, so I am guessing they are pretty worn.)
    I know that there is a flexible line between the old mechanical fuel pump (lift pump????) and the fuel filter. Dad says this was originally metal, but when he replaced the fuel pump at some time in the past it got kinked, so he cut out the bad part and replaced it with a flexible hose. I am going to replace this on Saturday.
    My question is, are there any other areas I need to replace or look at that could let air in the system?
     
  2. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    It could be the tank selector valve (FSV). They've been known to allow air into the system.
    Also, it's amazing that your truck is still running with 200,000+ miles on the pump and injectors. These should be replaced as a set since they wear at the same rate. Once those have been replaced and your timing is set, you'll feel like you have a totally different truck. There's only a handful of known good places to get a quality rebuild on your pump and injectors. Fortunately, all but one are on this forum. They are Thewespaul (Wes), Typ4 (Russ), and Agnem (Mel). I've used their user names and their real names so that you can send them a PM if you want to. The other one is Justin Anderson at R&D IDI Performance. All four are busy and no matter how you try to get a hold of them, they may not be the easiest to reach, but don't give up. They're not cheap, but cheap parts give you cheap performance. A lot (maybe most) of us have made the mistake of paying for cheap fuel parts and all have ended up paying for the quality parts afterwards.
     
    Exhumis and frankenwrench like this.
  3. Cubey

    Cubey Full timer RVer

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    There is a return line on the back side of the engine, buried deep. Here it is on my RV, where it's easy to get to. The hose was removed in his pic but the red line shows where it would be. It connects all the return line caps/hoses to a hard line heading back to the tanks:

    upload_2020-9-16_23-33-10.png


    Did you get the short hose at the lift pump? The green line shows the hose routing (on my RV). The short one with a hose barb on the pump is the inlet, the outlet is threaded so if yours has a soft line, it'll have a fitting in the fuel pump where the hard line shows:

    upload_2020-9-16_23-38-24.png
     
  4. Jon Sherrod

    Jon Sherrod Registered User

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    Cubey, I have already replaced the return line hose on the back side of the motor. I did not know about the short hose from the frame to the lift pump. I will replace it this weekend when I replace the one my dad put in between the pump and the filter. I will also take a look at the selector switch.

    IDIBRONCO, injectors are definitely on my list of things to replace. I am guessing that a large part of my rough running is an injector as the vibration on the engine is very consistent and leads me to believe it is one cylinder laying out. I wanted to eliminate as many of the air issues in the fuel before I started on that project. Truth be told, I am also a little worried about trying to get the injectors out since to my knowledge they have never been taken out of the truck. Dad did have the injector pump rebuilt by a diesel shop in his hometown at some point, not many miles ago (although many years ago) because it was leaking. He doesn't think they replaced the injectors at that time, but he doesn't really know. I have been running some injector cleaner in the fuel to see if it would help any, but with the air issues I have been having, I really can't tell it has made much difference. I have also only put on about 250 miles on the truck since starting to use the injector cleaner in the fuel.
     
  5. Noiseydiesel

    Noiseydiesel Full Access Member

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    I got new injectors through Oregon Fuel injection in Eugene, Ore. They also did my pump and turbo.
     
  6. YJMike92

    YJMike92 Full Access Member

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    I suggest you give a compression test some consideration. It would be a good thing to check with that uneven idle you mentioned.
     
  7. Macrobb

    Macrobb Full Access Member

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    Just a heads up, replacing injectors with a worn pump is not a good idea. Why? As the IP wears, timing gets retarded, but is counteracted somewhat by the injectors wearing and making it easier on the IP to inject(comparatively advancing the timing).
    Add a new set of injectors with the worn pump, and you end up with /really/ retarded timing.

    Usually, to make something like this work at all, you have to advance the timing a /lot/. Usually at least 6 degrees, something really hard to do by rotating the IP; the lines have to twist to new spots and it's really hard to get things tight and angled without stressing things too much.
    I usually end up skipping the IP gear one tooth ahead to make something like this work, but again, it's more of a "bandaid" than a "fix" - the true "fix" is to replace both at once.
     

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