Sucking air into fuel filter

[davidmartin720]

I have a Hunter with 2litre DOHC EFI Ford engine built in 1996. In the 4 months I have owned this car it does not pull as well, at times, as I thought it should. Air is being drawn into Fuel filter, the one with a glass tube between the swirl pot and the HP fuel pump. I have fitted a new replacement Red Top Facet pump [like for like] and still have the same problem. If I disconnect the wires to the rear pump the engine runs and no air is drawn in. Why ???? The rear pipe has current when priming then zero volts and then current again when running. Will it do any harm with the front pump pulling fuel through a stationary, disconnected electrics, rear pump. The front pump is noisy and I have ordered a new one but loathe to fit it in case of ruining the new one. I have checked the tank connections are correct. Just a thought, in September last year the previous owner's garage replaced 4 feet of fuel pipe, mind you they also replaced the front flexible brake hoses, which failed the MOT this time due to catching the front tyres on 3/4 - full lock !!!! The swirl pot is the squarish one with 3 connections on the top and an outlet connection at the bottom to the fuel filter. David.

[philcoyle]

Re: Sucking air into fuel filter

Hi David,
The power to the pump when you switch on is correct, the pump runs for a couple of seconds and then stops.
The ecu is waiting for all switches and sensors to send back info if all is correct then it will energise the fuel pump relay and the ecu relay when you turn the engine over, so all is well power wise.
I would not advise running a pump on its own as the effort of drawing fuel will possibly be enough to burn it out if run long enough. That's why it has two pumps, low pressure pump from the bottom of the tank usually gravity fed, pumps fuel to the high pressure pump to keep fuel rail pressure at about 4.5-5bars on priming, and 3 bars (45psi) when engine running, this pressure is maintained by the fuel pressure regulator and returns to the tank.
If it is drawing in air it suggests to me that you need to investigate if the pipes are fitted correctly, and check the pick up pipe and filter in the tank. A photo may help as my ESP is a little dim lately.
Phil

A rough guide fuel wise is, gravity feed to low pressure pump, LP to high pressure pump, HP to (swirl pot) fuel rail and then to pressure regulator ,return pipe to tank.

[cameronfurnival]

Re: Sucking air into fuel filter

As Phil says...
also...replace the hp fuel hoses and use new proper fuel pipe clips - it cheap and should rule out any cracking in the hoses - use SAE 30R9 specification. hth

[greyV8pete]

Re: Sucking air into fuel filter

...........................

................A rough guide fuel wise is, gravity feed to low pressure pump, LP to high pressure pump, HP to (swirl pot) fuel rail and then to pressure regulator ,return pipe to tank.

On my Hunter V8 it goes : Gravity to LP pump; LP pump with integral filter feeds constantly to Swirl pot (excess recirculates back to tank); HP pump feeds, via glass filter, from swirl pot to fuel rail: Fuel pressure regulator returns fuel to swirl pot.

My tank has the supply from an elbow at the bottom of the tank and the return goes in near the top of the tank, in the recessed area behind the diff.

Sytec recommend 10mm feed unions to HP pump to avoid cavitation (which will show as gas bubbles). An internally collapsed hose from the filter to the HP pump could do the same. Also the HP filter and its connections should be large enough not to restrict flow.

Final thought. What is the bore size of the connector that the garage has used to join on the 4ft of replaced fuel line? If it is too small it could starve the swirl pot of fuel and force the HP pump to suck fuel (and some air) up both LP lines? Peter.

[Alan c]

Re: Sucking air into fuel filter

My fuel filter 30% full of air (just an air lock) as long as there is fuel flow (ie outlet is under fuel level) its OK- mine works fine

[davidmartin720]

Re: Sucking air into fuel filter

Many thanks for all the comments, information and advice. I have removed the Swirl Pot and checked it is clear of any foreign material and also the outlet to the HP pump is from near the bottom. The fuel tank pick up is a copper pipe from the top of the tank into an added sump on the bottom of the tank and it is clear and as far as I can see, no muck in tank. My next jobs are to change the pipe from the tank pick up to the rear pump. Check to see whether fuel flows freely from the feed pipe to the Swirl Pot. Too much on today, "How did we ever find time to go to work" !!!!!! Sorry I cannot put any pictures on as I do not know how. David.

[philcoyle]

Re: Sucking air into fuel filter

Hi David,
I'm a little bit concerned about your pick up pipe and the L.P. To me it would seem like a mismatch as I thought that the L.P. was gravity fed from the bottom of the tank, and so I really don't see how it can drag fuel uphill to feed the fuel system. I think this set up needs investigating or enquiries made from other chaps with the same model. Having to lift fuel with the wrong type of pump instead of being gravity fed can have a dramatic loss of power, a gravity fed pump would struggle to LIFT fuel. The high pressure pump has probably been compensating and it is possibly on its way out as you say its noisy.
I don't suppose you can recall if your power losses co-inside with fuel tank levels, i.e. full tank =runs well, empty tank= loss of power and air being drawn in.

Also there is the possibility that this car had a dohc EFi engine fitted using the old carburettor engine fuel tank, which is why the fuel pipes come out of the top of the tank and not the bottom as per EFi tank. Two very different tanks and if this is the case once you replace the tank with the correct one, well, hold on to your hat. I don't think you will need to change much fuel pipe wise maybe relocate the Low Pressure pump to where it should be, a word of caution it may need replacing as it has probably had a hard life trying to perform in a way it was not meant too.
So tank= should be for EFi.
L.P. may need changing, or get one from the breakers where you get your tank.
Grin factor =exceptional.
New H.P.as well?
Phil

[Mike]

Re: Sucking air into fuel filter

Sytec advised me that low pressure pumps are not designed to lift - so you do need to make some changes.

Replacing the fuel tank is not quite as straightforward as Phil suggests though - Cabrio tanks are a Marlin bespoke item - not something you can buy off the shelf.

Having said that, if you know, or can find, a local engineering company that regularly weld aluminium, it should be a quick and easy job to drill a hole and weld a short section of 10mm, or better still 12mm tube to the lowest part of the tank (horizontally facing towards the front of the car).



[IMG]

I had an aluminium sump with collar welded on to my tank so that I could screw in a proper 12mm union (as advised by Sytec for a 200HP engine), but a simple piece of 10mm thin walled aluminium tube will be sufficient for your engine.
Connect this to your low pressure pump, and gravity will do the rest.

Sytec also told me that it is easy to burn out the pump vanes by running it dry - the fuel acts as a coolant, and without it, the vane tips melt very readily, and the pump loses pressure/volume - so it would seem prudent to change your low pressure pump for peace of mind.

[philcoyle]

Re: Sucking air into fuel filter

So very well put.
I was confusing your tank with Ford tanks in my minds eye and I could see the difference between carb and EFi.
You must forgive my grey moment when I forgot we were talking about a Marlin.
Your pumps will definitely need changing as they have been trying to do a job they were not designed to do as I mentioned earlier.

I will now sit back and let the more knowledgeable take over now I have diagnosed your problem. Don't give up hope, it is fixable.
Phil.


It may help you if you let people know which part of the world you are in, perhaps they could give you some hands on experience,

[peterboat]

Re: Sucking air into fuel filter

I have a hunter as well 2.3 efi. I changed the pump a few months ago [high pressure], it has no low pressure pump or a swirl pot, it has a sump in the tank which the high pressure pump collects its fuel from. The system works ok so why did Marlin put 2 different systems on their injected cars?

[davidmartin720]

Re: Sucking air into fuel filter

What a lot of replies, thank you everybody. Just a thought, as my engine does not suck air with the rear pump having the electric feed removed, and "Peterboat's" car only has one pump, what would happen if I put a new length of pipe from the tank outlet to the copper pipe that goes through the tunnel to feed the HP pump. By the way I have a new HP pump delivered today in case of trouble on the road !!!! David. I am in Somerset near Langport.

[philcoyle]

Re: Sucking air into fuel filter

Hi David,
I would have a word with FSE fuel pumps and explain what you want to do, draw fuel up from the tank and feed it at high pressure ( 3 bar) engine running but 5 bar at key on only engine not running, the engine size 2 litres+ and see what they suggest.
My Roadster only has one pump it's IN the tank, no swirl pot but the jam pot Sierra filter (holds about 1ltr) is right next to the fuel rail. The in tank pump is for a Ford Puma 2ltr and copes well, don't make the mistake of buying a lookey likey pump you will regret it, I know!
The choice is yours open the box or take the money, ignore me. Do your homework anything is possible, is there a high pressure pump rated to 5 bars that will lift fuel out of the tank and maintain 3 bars at the fuel rail? The pressure regulator will take care of the rest. Everybody will now start looking, watch this space.
Phil.


Ask about the Walbro GSL393 competition pump, does it lift as well as push, at £107 it isn't cheap but will save a mountain of work if it does the job, draw fuel out push fuel to rail, take note of the max distance from tank.

[danny_nelson]

Re: Sucking air into fuel filter

Marlin tried many different arrangements to fuel and cooling systems, during development of their factory built cars.

[Mike]

Re: Sucking air into fuel filter

What a lot of replies, thank you everybody. Just a thought, as my engine does not suck air with the rear pump having the electric feed removed, and "Peterboat's" car only has one pump, what would happen if I put a new length of pipe from the tank outlet to the copper pipe that goes through the tunnel to feed the HP pump. By the way I have a new HP pump delivered today in case of trouble on the road !!!! David. I am in Somerset near Langport.

Not a good idea!

Your high pressure (HP) pump is just that : it is designed to generate pressure, and is not suited to pulling fuel a long way, particularly if it has to lift it out of the tank.

Although your system, and Peter's are different, they are both designed correctly to work.

An HP pump should never be starved of fuel - you may lose engine power temporarily, as fuel is not delivered to the injectors, and/or you will ruin the HP pump vanes.

There are two ways to ensure your HP pump always has a supply:
Either, a LP pump feeding a swirl pot, guaranteeing a supply even in severe corners
Or a sump in the bottom of the tank which will not be purged in tight corners feeding a pump close by.
(most modern petrol engine cars have a single HP pump in-tank these days)

The more you report your issues the more it looks likely that your LP feed is causing your problems: either it is allowing air to be sucked in as you corner on medium/low fuel, or its flow capacity is insufficient causing the pump to cavitate.

At the risk of repeating the advice given, create a gravity feed from the bottom of your tank, and make sure the pipe is capable of a flow rate in excess of your Low Pressure pump delivery rate (it will surprise you how much fuel it can shift!).

What minimum internal bore has your feed pipe?

[greyV8pete]

Re: Sucking air into fuel filter

Marlin tried many different arrangements to fuel and cooling systems, during development of their factory built cars.

And air intake systems too! I will post separately my latest incarnation using a cold air intake from the front. It's looking even more crowded under the bonnet now! Hopefully finished tomorrow. Peter.