Ash.Witty Posted April 20, 2014 Share Posted April 20, 2014 Last year I got my cummins powered 110 on the road with no problems and about 2000 miles on the clock. At the moment I have a low pressure petrol fuel pump supplying diesel to a swirl pot mounted on my bulkhead next to the heater. It's got four ports, lowest port supply to the engines lift pump, second injection pump return, third fuel supply from tank, top fuel return to tank. The low pressure pump has been working faultlessly to date but I have noticed the pitch varies when running and want to know if this is normal or its possibly on its way out. Is diesel thicker than petrol etc and potentially killing my pump? The pump is constantly supplying the swirl pot and then returning to the tank with no restrictions could this potentially cause a failure? Do carb v8's have a fuel return line and if not should I block the tank return line off? If I was to return the fuel system back to standard same as a Tdi how much diesel would I need to keep in the tank when off road to prevent air being drawn into the system and do Tdi's suffer from this? I'm just trying to work out whether to bin the electric pump or not and revert back to the Tdi style fuel system. Quote Link to comment Share on other sites More sharing options...
robertspark Posted April 21, 2014 Share Posted April 21, 2014 It's got four ports, lowest port supply to the engines lift pump, second injection pump return, third fuel supply from tank, top fuel return to tank. Plumbed right, you could swap the middle two around, but it should not make much difference. Do carb v8's have a fuel return line and if not should I block the tank return line off? Yes Noise / pitch / pump running on diesel longevity .... no idea .... anything else would be a guess (check LP pump has non-return valve and not pulling air to start (if tank still full after it's been standing a while?). I guess the pump pitch may change depending upon how full the pot is and how much is returning back to the tank via the more restrictive return pipeline. Quote Link to comment Share on other sites More sharing options...
Team Idris Posted April 21, 2014 Share Posted April 21, 2014 The return should have a restriction or the electric pump will run too much? The facet runs all the time as do the gear pumps, but the sprung-diaphragm pumps only run when the pressure drops (Old SU etc). JCB had a mechanical lift pump from the tank that fed the filter housing. The filter housing had a small bored return line in the top of the housing. It maintained enough pressure to keep the injector pumps transfer pump primed and happy. Which is kind of what you haven't got? I guess you need to build it to make sure the old fuel tank pump has the life it was designed for? Quote Link to comment Share on other sites More sharing options...
Ash.Witty Posted April 21, 2014 Author Share Posted April 21, 2014 That's sounding more like it, a small restriction so it has a bit of load rather than running flat out all the time. I think the pipes from the pump and back to the tank are 8mm, bearing in mind its feeding a 5.9L diesel which only revs to 2500rpm vs the 5,500 of the old 4.2V8 should mean the pump is man enough to cope with the supply. What size restriction do you think would be suitable, 8 down to 2 or 3mm on the return line? Quote Link to comment Share on other sites More sharing options...
zim Posted April 21, 2014 Share Posted April 21, 2014 I've run mine in my challenge truck (petrol) for the last 5 years like you say. The only time we've killed a pump was when we ran out of fuel and only realised once the swirl pot was empty (meaning the low pressure pump must have been running for a good 20 mins or so dry - walters arena is a big site when walking !). I don't have a restriction on the return to tank. I just run a normal solid state facet. G Quote Link to comment Share on other sites More sharing options...
Ash.Witty Posted April 21, 2014 Author Share Posted April 21, 2014 Cheers Zim, its a normal petrol defender in tank pump, maybe I need a decent brand external pump, which would be easier to change in the field and I could bypass if worst came to worst. The inline injection pump is very sensitive to getting a slug of air through it as it opperated about 10psi per 1000rpm and the drop in pressure either bogs the engine down or stalls if on idle which is what I don't want to happen at an off road site etc. as its a pig to bleed. Quote Link to comment Share on other sites More sharing options...
zim Posted April 21, 2014 Share Posted April 21, 2014 I suppose it is a cummins :p :p Powerstrokes have 12v pumps Quote Link to comment Share on other sites More sharing options...
smallfry Posted April 21, 2014 Share Posted April 21, 2014 I wouldnt have thought a swirl pot is necessary, just a restricted return. I looked at the one in my factory V8 a couple of weeks ago and IIRC the hole was about 2mm. Didnt take THAT much notice though. As diesel is a bit more viscous, try it at 3mm as you say ? Quote Link to comment Share on other sites More sharing options...
Team Idris Posted April 22, 2014 Share Posted April 22, 2014 In theory the hole only needs to be big enough to let the air out? Although it was an orifice disaster, (finishing in me making a sprung return valve to hold back 3psi at the carbs), I found the best way is to get as small a hole as possible and work upward in size. I filled the end of a brass fitting with solder so it was easy to drill 1mm Quote Link to comment Share on other sites More sharing options...
Tanuki Posted April 22, 2014 Share Posted April 22, 2014 To make up a restrictor for a fuel-return line my easy way was - get the non-threaded bit of an old bolt that's a tightish fit in the rubber fuel-hose you're using, drill a hole down its length, tap one end of this hole and screw in an old jet from a dead SIIa Solex carb. Quote Link to comment Share on other sites More sharing options...
robertspark Posted April 22, 2014 Share Posted April 22, 2014 the return line serves two purposes 1) (most important) ... stops the pump pumping against a closed head (as the fluid flow aides in cooling the pump) 2) remove air. The restriction does not need to be scientific for a swirl pot.... as you have a secondary injection pump with it's own regulated return to the swirl pot. By slowing down the fuel flow back to the tank too much (too small a hole), you may end up with a pump pumping a pump given the pressure in the tank will be higher. In reality the issue is probably minor given its a low pressure pump (from the tank to the swirl pot) ... 3mm should be fine, given it's 25% free area of the 6mm return pipeline... 2mm is 11% free area (equivalent diameter) and may be a little small (no science, just a guess). Other than aerating the fuel and potentially heating the fuel in the tank (density change) from high fuel circulation via the swirl pot in the warm engine compartment and back to the tank, I can't see too much of an issue with no restriction on the return (given the inlet from the tank is 8mm, and return 6mm so there is already a minor restriction, albeit a small one). An M6 bolt without it's head forced into the 6mm return hose with a 3mm hole drilled in it should be fine as an orifice and offer some resistance. (as Tanuki above) Quote Link to comment Share on other sites More sharing options...
Ash.Witty Posted April 22, 2014 Author Share Posted April 22, 2014 I think I will try fitting a chopped M8 bolt with a 3mm hole drilled in next weekend and see if the pump pitch stays constant rather than varying up and down. Also I think I'm going to cut an access hole in the tub so if or when it does fail it means I'm not going to have to drop the tank to replace it. Quote Link to comment Share on other sites More sharing options...
Team Idris Posted April 23, 2014 Share Posted April 23, 2014 If a 3mm hole in a bolt is too big, hit either side of the hole with a centre punch to close it a bit, to save drilling another one. Quote Link to comment Share on other sites More sharing options...
Ash.Witty Posted April 24, 2014 Author Share Posted April 24, 2014 Nice tip Quote Link to comment Share on other sites More sharing options...
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