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Thread: mechanical fuel pump woes

  1. #1

    Default mechanical fuel pump woes

    Hey guys, this is my first post and although I have looked at the previous posts, I havent found the info im looking for. anyway, I have a 72 240z that I just recently purchased. It has been sitting for well over 15 years. I have had it for about 2 weeks now and I have just decided to try and get her started. After some fiddling, I managed to get it to turn over. It wouldnt start, I was getting spark so I begane investigating. I found that the fuel pump was faulty. So, I took it off the car, took the pump apart and cleaned everything out so it worked as it was supposed to. When it was all put together, It worked fine when I pumped it in my hands. However when I put it onto the car it didnt work. This worries me a bit because I know the pump runs off the cam, and since it wont pump when on the car, this leads me to believe the cam lobe has become flattened and can no longer push the lever far enough to pump sufficiently. Im curious if this sounds right, or if the problem is common. thanks guys!

  2. #2
    philo "Z" opher Zedrally's Avatar
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    Never heard of a flattened lobe.
    Have you checked the filter?
    That and rust in the tank is a common problem in cars that have been sitting for so many years.
    Considering the period of time the car has been sitting I would suggest dropping the tank [it's not difficult, do a search for more info], cleaning it out etc, changing filters, and blowing out the fuel lines.
    MOM
    Mike of the Mire

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  3. #3
    Registered User MikeW's Avatar
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    Quote Originally Posted by seventytwo240z
    When it was all put together, It worked fine when I pumped it in my hands. However when I put it onto the car it didnt work. This worries me a bit because I know the pump runs off the cam, and since it wont pump when on the car, this leads me to believe the cam lobe has become flattened and can no longer push the lever far enough to pump sufficiently.
    As I recall you can take off the valve cover and easily see the offset cam lobe. However, before you do that, are you sure the fuel is actually getting to the pump? Since the car sat for so long you've presumably drained the bad fuel, blown out the lines with compressed air, and added fresh fuel.
    -Mike
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  4. #4

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    actually what I did was put fuel in a small container (an arixona tea bottle) and put the suction hose into the fuel. I couldnt get any fuel to suck into the pump when on the car. However when I tried pumping it by hand, off the car, fuel pumped easily. This is the only reason I suspect a cam lobe to be at fault. It just doesnt seem like the lever on the pump is being pressed far enough in by the cam to allow proper pumping. Maybe ill have to take the valve cover off to inspect further.

  5. #5
    Automotive Addict zman525's Avatar
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    wait wait wait... this happened to me on my 72 240 aswell.. Check the arm to the mechanical fuel pump that is suppose to be pushing on the lobe, make sure it has downward force on it... This is EXACTLY what mine did and i just loosened it all up and she pumped like she just came off the showroom floor

  6. #6

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    Im not quite sure what you mean? do you mean when the pump is on the car, to make sure the arm has force on the cam lobe? if so, how exactly do I check this. I know the pump arm will move about 3/4 inch before it starts pumping, when I am checking it by hand. It only feels like the arm has force on it once I move it the initial 3/4 inch.

  7. #7
    Registered User Curtis240Z's Avatar
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    There is a offset socket under the cam gear bolt that drives the fuel pump. Assuming it is there, you must make sure you have the fuel pump arm riding on it, NOT below it or the fuel pump will not operate.

  8. #8
    Automotive Addict zman525's Avatar
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    kinda what i ment, but just take it out and move it up and down when u push up and let go does it fly back down? if not then it needs to be cleaned and lubed, and yes when you put it back in make sure its ontop of the lobe

  9. #9
    Supporting Member ChrisA's Avatar
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    If you dont want to take the v/c off, shine a light in the fuel pump hole and look at the eccentric on the front of the cam. If you can rotate the engine while looking, you can examine the eccentric on a complete rotation. You could rotate the motor till the "bump" on the eccentric is towards the pump hole, then when you install the pump you can kind of feel the arm of the pump contact the eccentric. You have to push kind of firmly against the pump to depress the lever and slide it onto the studs in the head.

    Hope that makes sense and helps you somewhat.

    Chris
    1973 240Z HLS30-156693

  10. #10
    Former frequent poster sblake01's Avatar
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    They're talking about the fuel pump drive cam shown as #9 in this scan.
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  11. #11
    Supporting Member ChrisA's Avatar
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    Thanks Stephen, didnt have any pictures here at work.

    Chris
    1973 240Z HLS30-156693

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