MF135 injector pump diagnosis and repair?

Discussion in 'Classic Machinery' started by Dry Rot, Jul 12, 2018.

  1. Dry Rot

    Dry Rot Member

    I inadvertently ran my (1974?) MF135 with the fuel tap shut off. It ran for a while, then stopped from lack of fuel -- obviously!

    I have bled the system and plenty of fuel is coming out of the vent screws on the CAV injector pump but the engine won't fire up. It usually starts up on the first turn of the key.

    There is plenty of information on the Internet, in fact far too much! But, assuming it is the pump, how difficult to repair myself? I'm guessing, running dry may have bust a seal.

    Haven't checked to see if fuel is coming out at the injectors yet but after doing a quick search on here it seemed the sensible thing to do was consult the experts! So, what do I do next? I gather a specialist will want a few hundred to repair.:(
  2. MrNoo

    MrNoo Member

    You'll need to bleed the injector pipes, just crack them off and crank it over (obviously with the stop button pushed in) once diesel starts to flow, tighten them and you should be in business, not heard of damaging a pump from running out of fuel.
  3. X344chap

    X344chap Member

    Central Scotland

    CAV DPA pump?

    Will just be needing bled at the injectors.

    V easy to overhaul for not much money - e.g. transfer pump vanes are £4.80 the pair which is a common wearing part.

    Its not a black art unless you want to start and adjust metering - for which you need a special rig.

    Best video i found for doing this is this one

  4. Dry Rot

    Dry Rot Member

    Slackened one pipe.

    Cranked 'er over. Nothing! Not even some diesel.

    "I bet it's the fudging pump".:mad:

    The words were no sooner out of my mouth when she fired up on two cylinders!

    Tightened connector and now everything is going like a dream!

    Thanks TFF experts! I knew you wouldn't let me down!:)
  5. manhill

    manhill Member

    Fellow sufferer here!
    Can't seem to get a decent pressure at the bleed valves by priming with the lift pump. The main filter and regulator filter are clear and the regulation bits in the end plate seem ok. Loosened 2 injector pipes and fuel is pulsing out but not sure if the pressure is ok. Cranking with the engine seems to empty the pump body and no smoke shows at the exhaust. Tractor has been getting harder to start the past week. Output from lift pump seems ok and no air bubbles showing when drained into a bottle at the injection pump connector so that should eliminate the filter. A bit baffled so here's my attempt at an idiots guide to step by step fault finding, feel free to correct
    1) prime the lift pump 10 times and slacken the lower bleed valve , release any air and tighten. Same with top bleed valve. Prime again, remove bleed valve and watch fuel squirt about 3 feet. Same with top valve. This proves the whole system up to the transfer pump onwards. Low pressure here could be due to lift pump, regulator valve/filter in end plate, main fuel filter or air. No point looking further until the main pump body is full and pressured?
    2)transfer pump, hydraulic pump, metering valve can only be checked for operation by cranking engine and loosening injector pipe to see if the spurts look ok. Smoke should be seen anyway at this stage anyway.

    My suspicions from past problems are always around the main body fuel quantity and pressure. I suppose my next check is to remove the end plate and see if priming gives a good pressure here.

    The videos are great for overhauling the pumps but tracing faults can be a bit tricky and info seems a bit sparse.
    Grateful for any suggestions.
  6. Dry Rot

    Dry Rot Member

    I once had a choked manual lift pump. It's not that, is it? I think there's a filter in there. If the fuel isn't coming out with some force, I'd suspect that.

    Prior to my problem (above) I had dirt in the filter above the fuel stop cock in the tank. That also reduced the force that fuel came out when bleeding.

    Can't suggest anything else, sorry. But good luck. It gets frustrating!
  7. Mursal

    Mursal Member

    Also there will be a filter under that lads finger in the above video.
    Under the feed pipe from the lift pump as it goes into the injector pump.
    Just loosen the fitting and lift it out to clean, be careful as there will be a valve living down at the bottom.

    We leave the bleeder on the injector pump open while priming, the one on the round part of the pump is the most important.
  8. tomlad

    tomlad Member

    nr. preston
    In the lift pump theres 2 one way valves
    About 3/4" round one facing each way to make the pump. Ive had them pop loose so it isn't pumping properly. Wouldn't let in air but lower power of pump.
    Biggest cause of fuel problems on my dexta was shite in tank blocking filter in tap . U could blow back to clear but that isn't solving anything
  9. manhill

    manhill Member

    I usually wash out the pump under the tap. A little bit of dirt in the tiny diaphragm valve can make the pump appear ok but won't pump enough. I usually test this by sucking and blowing on it's port to make sure it doesn't leak.
  10. manhill

    manhill Member

    Update: End plate removed and no blockage. Plenty of fuel coming out when primed. Now getting smoke at exhaust but not a lot.
    Wondering now if the lift pump is not producing enough pressure so it's coming off again. Possibly got dirt in as the tank had got low.
  11. X344chap

    X344chap Member

    Central Scotland
    Start at the beginning and go through everything in order - dont make assumptions or cut corners or get distracted and jump to conclusions.

    I'm assuming this is also the CAV DPA pump.

    Plenty of clean fuel in the tank? Its not empty or contaminated with water, dirt etc

    Pencil filter at the tank connection - is this clean?

    Fuel pump - gauze clean and non return valves not jammed? - does it produce fuel when you manually pump it and crank it with the engine? I've seen a pump that pumps fine with the hand pump but the lever had enough wear on it so that it didnt get a full stroke when cranking with the key.

    Main filters - clean and plenty of fuel being pumped to the inlet through the filters to the outlet? Does excess fuel get returned to the tank when you are pumping the lift pump? Should be a pipe on top of filters back to tank usually tee'd into the injector leak off return.

    Connection to DPA injector pump - plenty fuel here?

    All pipework tight - no damp connections or drips ? Fuel out means air in.

    Now go through the pump itself.

    Is the strangler fully closed - i,e is the stop spindle on the pump in the right position? When you move it by hand does it feel connected inside?

    Bleed the two bleed valves - should be a steady stream of fuel coming out and no air.

    Crack all the injector pipes at the injectors - crank the engine and you should get a nice pop and squirt of diesel at each one.

    If the output is variable - then you may have a pump problem. At this point i'd nip them back up and crank to see if there is any smoke from the exhaust. I'd then probably give the tractor a tow in 4th gear to see if i can get smoke.

    After this i'd then take the end of the pump off to check the micro fine filter, plunger and transfer pump vanes. I'd catch the diesel in a clear tub and check for dirt in it.

    I'd then take the top cover off the pump and check the stop spindle operation.

    If still no joy then i;d get into the rollers and shoes that push the high pressure plungers that develop the 2000psi but you need a special tool for this. Its possible the plungers are sticky or stuck with dirt. Everything inside a DPA pump eventually goes brown with fine sediment over the years.
    classic cutter and Dry Rot like this.
  12. Mursal

    Mursal Member

    Thank you, that's good to know ................ (y)
  13. manhill

    manhill Member

  14. manhill

    manhill Member

  15. manhill

    manhill Member

    All good points. Ideally I would like to have a way to split the system simply and establish normal operation. Thinking that a pressure gauge on the input pipe to the CAV pump could prove all ok from the tank, through any pencil filters, lift pump, and main fuel filter in one go. That's a lot of possible faults covered by just connecting at the pump input. Next thing would be to establish a ballpark reading and see that it holds pressure. Now where's that old tyre pressure gauge!
    If that's good I guess the same pressure should be seen at the pump bleed valve.
    After that it gets a bit harder to check. I've had a sticking metering valve before and luckily it slackened when I opened the top cover, then there was little or no fuel getting to the injectors.
    Right, enough waffle, back to work!
  16. MrNoo

    MrNoo Member

    Check as others have said, flow from tank first, then through the valve and so forth, quite often you will get a flow (of sorts) but if left for a while will slow down, especially with the pencil filter in the tank and filter in lift pump. To be fair most injector pumps dont give a lot of bother, am sure you will find something simple. You could just put a separate gravity supply straight to the pump, that way alleviating anything upstream, you could then (if still have problems) say it was the pump or downstream from the gravity supply.
    The old Tef Fergies used to have no lift pump at all on the early ones and they worked fine, so you dont actually need much pressure, just a decent flow.
    Mursal likes this.
  17. milkloss

    milkloss Member

    East Sussex
    Got a pal with an old jcb that is a beggar to bleed and get going when it’s been run dry. We now just start and run it on some sniff for a minute and bingo.
  18. manhill

    manhill Member

    Would that be DPA type in the TEF? There seems to be a lot of effort into design of my CAV DPA to build up transfer pressure. Might be to reduce wear in the hydraulic bits. I don't know.
  19. manhill

    manhill Member

    Finally got her started. Opened all the injector pipe unions and saw fuel pulses. Eventually got smoke out the exhaust and a helping hand with easy start got her going.
    It takes a lot of cranking until the exhaust smokes so probably not out of the woods yet.
    Thank to all for the help.
  20. MrNoo

    MrNoo Member

    No, different pump but I do know that a lot of people who have just rebuilt 3.152 engines and run them for an hour or so using gravity feed to the pump before re-torquing the cylinder head down and re-doing the tappets, saves putting all the tank on and then having to take it all off again, so they must run ok on gravity feed. Just an idea to isolate/pinpoint more where the issue lies.

Share This Page