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View Full Version : fuel pre filter set up plan for common rail



jimi_h80
11th November 2012, 02:19 AM
Hi all, currently doing some night shifts and have scribbled down some rough notes and drawings of a plan to set up a fuel pre filter/separator for my 3L common rail GU. i have read a lot of posts about fitting lift pumps etc but all for DI motors and haven't seen a lot about fitting any pressure gauges etc to prove the need (didn't look that hard admittedly).
my plan is to set up a 52 mm boost/vacuum gauge on the bonnet, plumed into low pressure fuel side before IP after factory filter, to see what normal pressures/vacuum are before fitting any pre filters, then see what draw is created when pre filter/separator installed, then add lift pump if needed.
i have semi bench tested this and think the air lock will work, to keep the diesel away from the gauge, am currently waiting for ordered boost/vacuum gauge (30 Hg to 15 PSI) to arrive before properly bench testing.

hopefully attached is a PDF of my scribbles

harro959
11th November 2012, 10:25 AM
Hi jimi
I love the way you are going about this mod. I am also very interested in the results and change in pressure for when you fit the extra filter. I have heard so much conflicting information on the effect an extra filter in the system will have on overall fuel pressure at the inlet side of the IP.

I have attached a pdf of the system i was thinking of installing on my td42 ute. I was going to install the extra pump and filter in an undertray box. The pressure relief valve is so that you can run the fuel pump to filter as a kidney loop if the engine isnt running.... i like this part because when you are in outback dodgy places you can fill your car up and then have the diesel being filtered whilst you are paying... then you can check to make sure that the diesel wasnt crap before you start your engine :)

The pressure relief valve is also to make sure that the diesel isnt being supplied at too high a pressure to the injector pump because in the IP for the 4.2 there is a timing advance mechanism that works off the internal pressure of the pump.

The purpose of the valves to the main and sub tank is multifold;
1. if you get a hole in your main you can draw from your sub
2. if you hole your main then you can pump from the main into the sub and vice versa.
3. You could also add an extra valve for the input and output lines so that you can pump diesel from a jerry can into either of your fuel tanks, or you could pump it out of either tank into jerrys or somone elses fuel tank.

Dont get me wrong i love my truck, but one of the things that i dont like is that you can only draw from the main tank, if you are 4wd and puncture it somehow, things are going to get real interesting really quick.

The purpose of the one way valve is that if the lift pump fails completely the IP will still be able to draw through the one way valve. Because as im sure you know the IP's use the diesel for cooling and if there is no diesel....

In regards to your design, the only point of problem i can see is that i dont know wether the pigtail will stop diesel getting to your gauge or not. But you have significantly reduced the cost of failure by mounting the gauge eternally.

jimi_h80
11th November 2012, 08:55 PM
harro
thanks for the reply and drawing, i will defiantly be looking into adding the kidney loop in the future (obviously will depend on weather i need to install a lift pump or not), bloody great idea!

The main reason i started looking into the pre filter was a mate of mine with CRD picked up some bad diesel on the Gibb river and done his IP in. cost him about 5k in the end, so i started reading into it and the more i read the more paranoid i got. Any way when Nissan repaired his bus they installed a ryco pre filter/separator, which is fair enough and he hasn't had any dramas since. But like i said the more i read into it the more i thought i'm not gonna just slap a filter in and hope for the best.

when i did the semi bench test the other night , i basically just ripped the small pressure gauge out of my air compressor regulator, plumbed a tube into it and tried to pump it up with a 50mL syringe full of water. i could only pump it up to about 10 psi before the syringe started leaking out the back end, but no water got past the air lock and into the gauge, plus 10-12 psi was only maybe 8 mL of water displaced into the tube (hence the pig tail design is purely for length). so as long as all the connections are air tight (should only need to be able to handle 30 Hg to 30 Psi max) the air lock should keep the diesel away from the gauge, but I'm not sure what affect diesel fumes will have on the gauge over time.

once the gauge turns up I'll plumb it all in, take some photos and post results.