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Thread: 4D55 Rebuild/Fuel Info

  1. #1

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    4D55 Rebuild/Fuel Info

    Hey guys, I'm new here, been browsing for a while but decided to join.

    I have an 84 Mighty Max with a 4D55 (it was a turbo but somewhere along its ownership, the turbo has been removed). It was running nicely until about 2 months ago, a 'squeeking/knocking' noise was coming from my engine and it seemed to be running on 3 cylinders. Not good! Tried the usual, valve, oil, belts checks and I couldn't figure out what was wrong.

    I then took my head off and rocking the truck back & forward in gear revealed that my #4 piston was only coming halfway up before dropping, well thats the 3 cylinder problem explained. Now for the knocking- I took the oil pan off and sure enough, the #4 rod bearing had disintegrated.

    So...I bought new rod bearings, main bearings, got my crankshaft re-sized, new piston rings (remember they are half keystone rings!), threw a new clutch on, new gasket set, valve stem oil seals etc & timing belt. I spent a few hours in the evenings working on it and after about a month, I had the engine rebuilt. So on Saturday I started it up, the engine was a bit noisy at first until the oil got pumped around, after 2-3 mins it got smooth. I let it get up to temp and it ran for around 10 mins.

    Heres where I'm confused: I shut the engine off and lowered it off the jack stands, went to crank it and not it won't crank. It fires up when I put some starter fluid in the air box so I know its a fuel issue. I thought maybe its airlocked but my fuel filter primer plunger is missing so I can't prime it. I took my injectors loose and I've cranked it a bunch and no fuel comes out, I even took my supply lines loose and filled them with fuel. I checked the power plug on my injection pump and I got 5.3v across 2 of the terminals so I *think* its getting the right power. I've checked in the book and I can see nothing about a fuel or transfer pump, do these engines have a fuel pump? Or do they work off a vacuum from the injection pump?

    Any help/suggestions would be appreciated!

    Thanks

  2. #2



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    You must have a way to prime it or you will never get it started. It's all air. You ran it out of fuel. An empty fuel filter not being filled with clean diesel will do this when changing it. You need to prime the lift pump and then bleed the injectors.
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  3. #3

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    Is there a way to prime it without the prime pump on the fuel filter? I have filled the fuel filter with diesel and the lines too

  4. #4



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    No. You must use the prime pump or if there is a lever on the mechanical pump that you can push to prime it. But I'm not sure if they have that like other diesels do. With out a primer you are kind of stuck tell you get a new one.
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  5. #5

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    I spotted one on ebay last night so I ordered it. Should be here by the weekend. I hope that fixes my fuel problem.

  6. #6



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    Once you get fuel to all the injectors it will start. It's just a pain to get it going. Have a good battery and a charger handy. Once you put on the primer pump you will be able to tell when fuel starts to reach the injection pump. It will be a little harder to pump. Then crack the injector lines at the injectors and start to crank it over. Look for good spurts of fuel. no air. Don't kill the starter. once it starts to get good squirts of fuel. Tighten up the first injector while cranking it. then work your way back. Some people will start with the line furthest away from the pump. But they are all the same length.
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  7. #7

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    ^Will do. Thanks for the advice, I will let you know how I get on with it.

  8. #8

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    Ok so I got my wee primer thingy today. I loosened my bleed screw, screwed the primer it onto the side of the fuel filter casing and started pumping......Nothing was happening, no fuel, I couldn't feel any pressure. I figured there was a rubber gasket or something missing so I botched one one on, that I had laying around and after a few attempts I had fuel/air coming out my bleed screw. Great!

    I pumped until no air was coming out, just a steady stream of fuel and I tightened the bleed screw back up.

    I then started pumping to fill the injector but I pumped and pumped and pumped and the primer wouldn't get hard or firm at all. Took my bleed screw loose and just fuel came out so I know I'm not sucking air in. At intervals I cranked my truck over for 10 seconds with my fuel injector line loose and no fuel was coming out of it.

    I took my rubber fuel pipe (from the fuel filter to the injection pump) loose at the injection pump, pumped my primer and fuel was coming out the pipe, all good. I put it back on, followed that line around and then loosened screw in the metal supply line going into the injector (just under the hose from the radiator), I pumped the primer and fuel is coming out, so I know fuel is entering the injection pump.

    I tightened that back up, pumped some more and still no firmness.

    After some deliberation..I took the fuel return line off the fuel rail and when I pump the primer, fuel is coming out of that pipe (from the injection pump)...is that meant to happen?? I blocked it off with a screw, to cap the hose and I had to take the other side of the return line (going from the injection pump to the tank) off and put another line with a screw capping it off, on there.

    With all the exits (return lines) blocked, I started pumping and the return line from the injection pump to the fuel rail with the screw capping it off, ended up splitting (its pretty old) because of the pressure (although the primer still wasn't getting firm) and fuel was dripping out, so at this point I give up for now to ask a few questions.

    -Is the fuel meant to come out of the injection pump and into the return lines when you pump the primer?
    -Is my timing messed up? (all my marks line up) I don't see how this would make a difference to priming the injection pump and the other problems I'm having.
    -Is my injection pump messed up? (its probably 15k miles old)
    -Or is there some other problem that I'm over looking?

    Thanks for any input/advice

  9. #9

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    I've now narrowed my problem down to a stuck plunger in my injection pump. I may rebuild it or I may get a new pump if one comes up at the right price.

  10. #10



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    If you have fuel coming out of everywhere except the injection lines then you may have stuck the plungers when you ran it out of fuel the first time. The diesel is what lubricates the pump.
    While the injector lines are off at the injectors and you pump the primer does any fuel come out of them?
    You should get something. As for stiff primer you might have already felt it but did not notice the change. Some systems are more noticeably then others. Then to make it worse some primer pumps use a spring to pump the fuel VS when you push on it. But since the line cracked from age then this one is when you push it. You may also here the spring in the return check valve rattling.
    But if fuel is coming out of the injectors with the line loose then it should be able to start to build up the pressure when cranking. Just keep in mind that the injection stroke is on a small amount and the hole line needs to fill up. Some systems the primer will push fuel out the injector lines when off some don't. It depends on the system. Feel free to call Margret at Diamond Diesel in West Sacramento to probe her knowledge of 25 years. She may have a trick others don't know about. All they do is injectors, pumps and turbos. She knows your Bosh better then anyone. I think there is a sticky or a link in the diesel section to them. She can also tell you why you don't want China pumps.
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  11. #11

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    Thanks for the info. I will give them a call shortly and let you know what they say.
    As for fuel coming out the injector lines when I prime the system, that does not happen. I loosened the screw at the plunger and fuel is coming out there when I pump my primer, so I know fuel is getting to the plunger but not making it past it to get to the injector lines. So this is why I think the plunger is stuck but it has only been 8-9 weeks since it was running so its strange that the plunger would stick in such a short time, although I use bio diesel so that could speed the sticking. The solenoid is clicking when I turn the key, although I will hook it up to 12v tonight just to make sure but I assume if its clicking, its working.

  12. #12

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    Well I ended up taking the pump off and taking it apart, much to my annoyance because I had just bolted everything together and set the timing. The Fulcrum lever pin was broke off, so no plunger movement. Ordered the part today so it should be here tomorrow.






  13. #13

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    Wow sorry about the massive pics.

  14. #14



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    Quote Originally Posted by stevyg View Post
    Wow sorry about the massive pics.
    Here is a fix to the pictures. http://www.mightyram50.net/vbulletin...izing-Software
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  15. #15

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    Thanks. Though I can't edit my posts yet

  16. #16



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    Since the board is 95% member supported, editing posts is part of the upgrade to members when they become a donator. Along with a hole bunch of other things. But thats just one of many reasons we have so many donators on the board. We just want to stay on the net. Soon we will have a factory manual section just for donators. It will be all factory manuals only available to the board donators and contributers. We are always looking for ways to make things better and get people involved more.
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  17. #17

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    ***** is right, when you run those out of fuel you run the risk of doing damage to the pump. Also a quick tip for anybody else with bleeding issues is to remove the 4 glow plugs and than crank the engine with the lines cracked loose. Without compression the engine will spin with no effort which means it turns much faster and does not kill the battery. Also once you tighten the lines you will see a mist of fuel blowing out of each glow plug port. BTW you will never find a new pump LOL! Where or who did you convince to sell you parts for the pump?? I just send mine out for rebuild as a home mechanic will never get it to work right ( No calibration machine, must be laboratory clean conditions etc...........)

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