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Air Leak Points Please

frank rabbets

frank rabbets

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Mar 1, 2010
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My 24v diesel now needs priming before it starts. Fuel is draining back into the tank due to air sucked to fuel system when not running. Could those who have found week points please start a list of points to look at.

Thanks
Frank
 
HI Frank

You could try this as a fix before finding the fault. The fuel is draining back away from the pump / filter. If you install a one way valve prior to the fuel filter so its pointing uphill both gravity and the fuel trying to go the wrong way will close the valve.

Got mine from one of my favourite toy shops - the hydraulics engineering firm.

5 min job, cost me £17 odd in parts (no doubt ebay would be cheaper).

Cut fuel line about approximately 3 inches right of fuel filter viewed as you are standing on nearside of truck.
One stainless steel jubilee clip on fuel line to right
one left of cut
slide in one way valve, with the out marking towards the fuel filter
(The one way valve should have 12 mm barbed ends)

tighten clips

pump primer, which for me did not prime first time
started truck
it stalled due no fuel, then the primer pumped as it should (go figure)

problem solved.


I dont really know cause but i suspect there is a diaphragm that is failing and letting air be drawn in. on boats i was taught to turn off the water pump before closing up for any period of time, then open the water taps to let the water drain and remove the pressure on the diaphragm ro prevent damage. I have wondered if the fuel pumps are similarly affected especially as trucks get older, and those that may not be driven regularly so there is pressure on a diaphragm that eventually starts to fail. Not suggesting that is what has happened, just theorising.

Chris J went further and installed small inline 100 micron fuel filter before check valve - said he had one that the ball valve got stuck open with some debris so filter would prevent this.

Good luck.
 
Thanks!

I had thought of a one way valve. Also thought of a low pressure pump by the tank but it would leak fuel through the problem if pressurised.

Frank
 
It might frank - thought its only going to pressurise when engine running and pulling fuel through. Pump pulls a lot of fuel through with a good quantity being used for cooling.

Chris did install a Wlbro on his 80 - I thinks its in the sticky maintenance thread. Im going to do the same but i might do an intank pump rather than the external one he mounted. He said it's made the truck really responsive as well.
 
I suddenly realise there may be a diaphragm in the priming pump. This may have failed. I think I shall take the fuel filter assembly off with the rubber pipes and put it on the airline with 2 psi and check for air coming out. Also fit a temporary clear filter to bypass it. But what particle size do I need !?

Thanks

Frank
 
Not sure

just did a quick search and this may help from this page:
http://www.pradopoint.com/archive/index ... 1e7f35b88a

not the bit about fuel restriction and warranty but mention is made of micron size...

in this section:
but any restriction in the fuel system... ie an added fuel filter, will void your toyota warranty, they need to flow 20-60 lts per hour in flow rate, putting a fuel filter inline restricts the fuel and causes damage to the fuel pump... currently to do a pump and injectors on a D4D inline 4 cylinder engine costs around $8K... Cooma diesel have a nifty device that will solve all your problems, give Dave a call at Cooma diesel. :roll:

This has been done to death on other forums. I remember posting here about the filter that I fitted to my last vehicle, and was shot down with the same arguments. I have done plenty of research lately, and the consensus is that a 20micron filter before the OE filter, and then a 2 micron filter after the OE filter is the way to go.

Good luck
 
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Or call stef or karl, buy another used filter mount and fit it whilst you investigate your current one?
 
Yes I would not run a non standard filter for a long time. The original is best. I would use the temporary filter for diagnosis and see if I could take apart the filter holder. I will see how much a new filter holder is and hope they quote me the wrong price.

Thanks
Frank
 
Second hand ones are just as likely to be stuffed as the original one. The diaphragm gets pin holes in it so I understand. Karl's solution is to fit a Transit van unit which has a decent primer pump. The Toyota replacement and even the Milner (non heated) ones are expensive. I bought a one way valve for about £3. Two clips - job done. No more complicated solution needed than that.

Chris
 
Thanks for that Chris. I've just found your ebay link. Is the heater important in UK?

Frank
 
Probably a dumb question but is the primer pump essentially the fuel filter housing, as in the part which the fuel filter mounts to?
 
I've taken the filter assy off together with pipes and held it in a vice with a long vertical clear tube connected to the inlet fuel pipe. I've bled it with the primer pump and blocked the engine supply pipe. Then I've connected a 10 psi airline to the vertical pipe and pressure has been on for 30 mins. The fuel level in the pipe has not dropped proving that no air is escaping from a hole in the assy instead of tell tale fuel. Also no fuel is coming out. The primer pump plunger is very hard to compress so must be under pressure and is not leaking.

Defo a fuel prob as pump is easy to push then hard, and after engine will start.

The air ingress is either in the injector pump assy or down toward the fuel tank [latter unlikely].

There must be a non return valve in the fuel filter head as fuel only flows easily in one direction , towards the engine, but I have not checked it yet. So the salient question is; in a healthy LC would fuel drain back out of the injector pump assy into the fuel tank and a non return valve is fitted in the filter head to stop this happening ?

Frank
 
I checked the fuel line to the tank with a head of diesel fuel and it held up well, which is what I thought. Also tested the non return valve in filter head by sucking from the tank side and it sealed OK. However I tested it with see through plastic pipe from the tank and primed this pipe until I could see the fuel level in the pipe and this gradually drops proving that the non return valve is the cause. Chris, do you think your type of non return valve would best be fitted on the engine supply pipe as my filter head assy does not leak fuel or air? This would give it filtered fuel.

Thanks

Frank
 
I think your logic is sound frank. I fitted mine where i did as PM. I wonder what has caused the valve to stick open and is there a way to free it up? A sharp tap or two springs to mind but i may be wrong?
 
I cannot get to the valve. The inlet pipe does not appear to be threaded and I do not want to strain it and cause a leak! There are two threaded plugs but one of them the inlet pipe is in the way, and they both need very thin walled spanners. So I have settled to fit a non return valve, Very pleased I definitely found the cause. I'll post result.

Frank
 
The one way valve is on the inlet pipe side of the filter housing. The pipe is impossible to remove. It looks as though the aluminium is cast around it.There are 2 threaded plugs in the housing but their apertures lead nowhere. It is therefore impossible to get at the valve. It takes almost no pressure to open the valve. The Thornycroft valve I have bought needs about 6 times the pressure to open so I will probably fit a weaker spring. I don't fancy the pick up pump straining if it can be avoided.

Frank
 
Sounds like the filter head non return valve is a non serviceable item then.

The one way valve i got take almost no pressure to open - not sure it even has a spring, i think its just a ball that as flows reverses it pulls shut (if thats an accurate description!)

I was blowing through it when i got it and it tok very little pressure to open it, and practically no suck for it to shut. I installed it in the rising part of the pipe in hope gravity will also assist... course the ball might float in diesel so that'll kill the gravity idea!!).
 
Do you have a contact where I can get one like yours; or a reference number?

Thanks
Frank
 
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