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Fuel cut-off solenoid and relay

Discussion in 'Fuel System & Electrics' started by GlennS, Sep 6, 2021.

  1. GlennS

    GlennS Member

    Messages:
    78
    Location:
    pheasants nest, nsw
    Hope you are all well and staying safe.

    I was reading the May-Jul 21 issue of VWA Magazine and on page 32 the Fuel Cut-Off article.

    I was thinking of doing the suggested install of a fuel cutoff solenoid and fuel pump relay. I have a standard mechanical fuel pump in my 75 Kombi.

    I am hoping someone in the club has already ventured down this path and can help me and probably others who would have read the article, but then be a bit lost what to buy and how to install, particularly in these lock down times when we can't visit our favourite VW shop etc. to ask these questions.

    So:
    1. Where to order a suitable solenoid and relay and what are the part names/numbers etc.?
    2. Where in the fuel line to install the solenoid and attach?
    3. Wiring the solenoid in, where and where to attach?

    Thanks for any advice.

    Glenn
     
  2. Barry

    Barry Well-Known Member

    Messages:
    6,003
    Location:
    Abbotsford NSW
    Last edited: Sep 6, 2021
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  3. T1 Terry

    T1 Terry Well-Known Member

    Messages:
    1,745
    Location:
    Mannum South Australia
    The only reason I can think of the need to use a fuel cut solenoid with a mechanical pump, is to stop the fuel dribbling through into the carbies, flooding the engine and diluting the oil, as well as making it a pig to start after a hot run shut down ......

    Any place that installs LPG for dual fuel vehicles will have the bits you need. The solenoid goes in the fuel line between the fuel pump and the carbies. It can be wired to the positive side of the ignition coil so it only opens when the ignition is turned on, so the tachometric relay isn't required ...... but it would stop fuel pouring into a fire via siphoning or pressure build up in the tank when the engine stopped turning but the ignition was still switch on .....
    Before I did the LPG conversion on Kombi, the whole hot run flooding in summer was a real nightmare, having the separate 3 way switch to change from LPG to no fuel to petrol worked a real treat, cut the fuel before turning the engine off so the carby bowl levels dropped a bit and the flooding problem went away .... caused a few embarrassing moments when I forgot to turn the switch back on though :oops:

    T1 Terry
     
  4. GlennS

    GlennS Member

    Messages:
    78
    Location:
    pheasants nest, nsw
    Thanks Terry and Barry. I have that problem of fuel getting through so just want to stop it happening.

    Has anyone ordered the required parts mentioned in the VWA magazine on line? In lockdown here.
     
  5. Mordred

    Mordred Super Moderator Staff Member

    Messages:
    3,011
    Location:
    Penna, Hobart
    Here are some options for you.

    https://bluelpg.com.au/shop/index.php?route=product/search&search=solenoid
    From there a pl40 or PL 40T or even a PL30 if you want to buy a couple of barbed fittings in a closer to your fuel line size. Somewhere like Pirtek can help you with those. This is an example, you might be able to find them cheaper elsewhere. Don't use teflon tape to seal the fittings. There are good sealants available for the job if you need it. You might need a little research to find the best fuel resistant one.

    Pierburg 721.440.51 is a good pump. 3-5 psi is the most pressure you will want and better if you can get lower, but the considerable additional cost of a proper fuel regulator (you need to get a good quality one as the cheap ones rarely are effective or reliable) is probably not worth it. Google search will find many inc Ebay. I think the Carter brand pump of the same rotary vane type is quite well respected too. Much better than the chinese rattle pumps.

    upload_2021-9-10_17-19-57.jpeg
    Try to get some Norma brand fuel clips like this. Sizes 10 11 12 or 13 depending on what fuel line you use. Might take a bit of searching but they are worth the effort as they don't damage the fuel line like the worm drive ones do.

    Lastly wire the clamps back to the carb in particular so that if the brass nipple starts to fall out (as they are just pressed in) it will stop it falling out completely. Just a bit of light gauge gardening steel wire will do, and wrap it around a screw or other fitting on the carb and through the clamp.

    Good luck

    Adrian
     
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  6. Barry

    Barry Well-Known Member

    Messages:
    6,003
    Location:
    Abbotsford NSW
    Glenn
    Do you have a Type 1 upright motor or a Type 4 pancake motor?
    What you are planning is a "patch" and not the solution.

    You either have a stuck needle and seat or a hole in the diaphragm of the pump.
     
    syncro likes this.
  7. T1 Terry

    T1 Terry Well-Known Member

    Messages:
    1,745
    Location:
    Mannum South Australia
    The problem I found was the fuel in the lines would heat up and raise the pressure to the point the needle and seats couldn't hold it back anymore. Once the fuel pours out of the fuel line, the pressure drops and any pressure built up in the fuel tank will push fresh fuel into the lines, cooling them, until no more could flow in, then the process started again until the engine or fuel tank cooled. The valves in the mechanical fuel pump will allow fuel to pass through the pump from the tank, but they will not allow it to flow back the other way.
    The rattle pumps at least have a spring behind the metal plunger, the pressure will compress this spring because the force is against the outer face of the metal piston .... add to that, there is blow by around these pistons so the pressure eventually makes it back to the fuel tank side of the pump. The fuel trapped between the shut off valve and the pump piston bleeds back first, the shut off valve has a pressure return valve built in to allow the pressure after the valve to bleed back through to the pump and that bleeds back through to the fuel tank.

    The Facet rattle pump and the many copies of it, have spring pressure some where between 7 psi and 5 psi .... when the pump is new and the spring and pump is cold ..... if you get more than 4 psi running on a hot motor I'd be very surprised. My rattle pump has been in there since the LPG conversion, well over 200,000km ago, still going strong and used every trip on the highway when my wife is driving to Adelaide, the LPG converter freezes when the throttle is held wide open for long periods of time :lol: I'm just as guilty as far as that goes .... Well it did work faultlessly until the last wiring up in smoke episode because the heater blow fan seized and shorted out ..... there didn't appear to be a fuse in that circuit wired back to the starter motor .... but every chance it's not original after all these yrs and kms.

    Approx. another 70,000km and Kombi will have covered the million kms on Australian roads ... as best as I can make out by looking back through the service records and km recorded at each NSW registration inspection. We have clocked up 400,000 plus of those kms in the 22 yrs or so that we have owned it. Certainly fits in the "driven not hidden" category.
     
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  8. syncro

    syncro Well-Known Member

    Messages:
    10,292
    Location:
    Southern Highlands
    1500 King on here can supply all of the parts that you want including clamps and fuel line. I can help you when restrictions allow.
     
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  9. GlennS

    GlennS Member

    Messages:
    78
    Location:
    pheasants nest, nsw
    Thanks all for the information and offers of help. Phill keep an eye out for me as I now have my plates, we just await that curtain for travel to open.
     
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  10. GlennS

    GlennS Member

    Messages:
    78
    Location:
    pheasants nest, nsw

    Thanks Adrian. I think I will go with PL40. The VWM article also suggests installing a relay. Any suggestions regarding that? I am sticking with my mechanical fuel pump for now. Thanks for your help.

    Glenn
     
  11. syncro

    syncro Well-Known Member

    Messages:
    10,292
    Location:
    Southern Highlands
    You shouldn't need a relay. A relay is only required if you fit an electric pump. If you do fit a relay you might as well fit a tachometric relay. You could also fit a hidden kill switch to the valve for security.
     
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  12. GlennS

    GlennS Member

    Messages:
    78
    Location:
    pheasants nest, nsw
    Thanks Phill
     

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