CAV problems.

Discussion in 'Classic Machinery' started by mikep, Aug 1, 2018.

  1. mikep

    mikep Member

    My JD combine has a CAV rotary pump which was rebuilt last year after it sheared it's head. Ran perfectly well all last season and the start of this, still perfect when running but starting had become a nightmare. It takes a starter motor frying length of time to start.
    No visible fuel runback from fillter (stanadyne) but fitted fuel one way valve anyway near fuel pump.
    Fuel pump fine (electric) good pressure and flow.
    New filter but old one crystal clear.
    Stopped and left parked in run position but no better.
    Fuel comes from the lower bleed but not upper.
    Left fuel tank cap off when stopped never noticed vacuum before.

    When you try to start it fires immediately but dies, then nothing for ages then a quick run then dies they another long churn and eventually starts and runs perfectly.

    Really getting nervous about this. I'm going to change the back plate for the filter and pipes but apart from that I'm out of ideas. Anyone?
  2. marco

    marco Member

    tipperary, ireland
    Try putting the non return valve as close to the tank as you can and try. If the fuel line is slightly porous it will run back from behind the one way vale back to tank. Worth a try surely and no cost?
  3. Mur Huwcun

    Mur Huwcun Member

    North West Wales
    To eliminate the pump issue fit a temporary tank on top of the engine or anywhere above and leave overnight?
    marco likes this.
  4. mikep

    mikep Member

    I have fitted an nrv just by the tank however it was a cheapo chinky one and I noticed this morning that there had been run back from the filter. Maybe the first thoughts were right just the solution faulty. I've put a mole grips on the pipe and will look in the morning.
    marco and Bloders like this.
  5. mikep

    mikep Member

    Will wait to see what Mr Mole finds out but a good idea.
  6. Timbo

    Timbo Member

    Gods County
    Lift pump diaphragm holed. Have it on mine about every 3 yrs. Vapormatic one for about £30 is the same as the jd one
    Flat 10, Mursal and davidroberts30 like this.
  7. Ioan annwyl

    Ioan annwyl Member

    What model jd?
  8. Ioan annwyl

    Ioan annwyl Member

    You said on another thread (jd engine) that you have replaced injector with an used one from another engine, did you replace the rubber seals on the return T pieces all 3.
    Not easy to change injector without disturbing adjacent T piece. Seals will leak and causing external leaks or an air leak allowing fuel to drain back, check thermostart reservoir, has the plastic or rubber pipe perished, also check steel pipe from filter housing around rear of engine where the steel clamp holds the pipe below the exhaust manifold, remove clamp and check pipe it will be worn, had dozens do this, seen them with cracks that won't leak diesel even when running, but will draw air when left overnight.
    Fitting a non return valve only cures the symptom not the cause.
    I assume it's 900 or 1000 series combine. Let us know how you get on.
  9. mikep

    mikep Member

    It's a1068h. Took mole grips of to park it last night and forget to put then on and it's drained below the filter element definitely leaking back through electric fuel pump and chinky nrv.
    What I can't understand is if air can get into the return how can that lead to the fuel leaking back unless it does it through the injector pump (didn't think that was possible) as the return doesn't go to the filter but straight back to the tank. The feed side is tank, pump, filter and injector pump with no return connection.
  10. I will repeat what has already been said and that is check for air leaks.... a few years ago we had problem with our old dexta playing up .. the problem was fixed when I tightened screws around lift pump and recently there was problem with our old sawbench with Petter PH 1 engine and the seal around glass bowl was problem
  11. I have just thought..... could there be problem in or around tank
  12. Mursal

    Mursal Member

    Also worth checking the leak off pipes on the injectors.
    Keep in mind air will enter where fuel may not necessarily leak out, especially with such ahead over the fuel tank.
    Put electric pump running before you go for a start ...........
    roger wilkinson likes this.
  13. Ioan annwyl

    Ioan annwyl Member

    Two pipes on tank, 1 feed, 1 return, any air drawn will allow fuel to run back down the pipes be it feed or return, if it is on the return side it can draw fuel from the injector pump. Replace the fuel line with a clear one as a temporary fix to see which hose empties, then replace with proper fuel hose.
    Still think it's T piece seals, or fuel filter to injector pump pipe.
    As Mursal said turn ignition on, wait 30 seconds does the clicking slow down, now does she start, or do you have to bleed the system. Do you have some dirt under the seals on the glass fuel filter?
  14. Mrtwhite59

    Mrtwhite59 Member

    Medway Kent
    FCC80E36-1B96-4D65-8155-527CA035DE40.jpeg Could this help anyone on here free to anyone who could make use of it
  15. Cowcalf

    Cowcalf Member

    North of Scotland
    either replace the pipes or if too hard, pump the fuel in reverse back to tank but block it before the tank then you may be able to see a leak when under pressure
  16. Flat 10

    Flat 10 Member

    Fen Edge
    It’s this. Used to have the exact same symptoms and replaced mech lift pump when it leaked diesel and cured the issue you describe
  17. manhill

    manhill Member

    I would forget about messing around with injector pipes etc.
    After my results yesterday, nothing will happen until transfer pressure is built up.
    Take off the top bleed valve and crank until the fuel gushes out (and I mean gushes),
    As soon as that happened on mine the engine started and ran while still gushing.
    This indicates to me the importance of transfer pressure.
    Having to crank fast on mine makes me wonder if the transfer pump vanes need replacing so off to injector shop later for advice.'
  18. Mursal

    Mursal Member

    Are you gravity feed to the transfer pump, or have you a lift pump fitted?
  19. Exfarmer

    Exfarmer Member

    Bury St Edmunds
    Fit an electric lift pump. Manycombines have this issue
  20. manhill

    manhill Member

    Electric/mechanical/gravity, it doesn't matter if air is leaking there or at the filters/lines. For diagnostic purposes a bottle feed into the DPA pump inlet will determine if the fault is in the pump or further back. Crank until she gushes a few feet. If no gushes, there is not enough transfer pressure so don't bother looking at the high pressure lines/injectors. May be the transfer pump worn or something in the regulator valve area. I think the transfer pump, like my Honda water pump needs that priming liquid before it will operate.

    Listen to me, talking like an expert now. It's just because I'm being driven by necessity.


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