Bleeding injectors, again!

[Aardvark]

My "air in the system" problem is now getting very much worse. I am getting about 10 to 20 miles between roadside bleeding sessions and its getting silly. Can anyone tell me definitively how the air gets into the system in the first place? At first it was number 2 that was the culprit. Now it is number 3 and rarely number 4 that is full of air. I don't need a link to the bleed off mod thanks. I know about that and can't do it due to access problems and cheap ass plastic connectors at the back. I have done almost every repair on my Mk5 myself but if I was in UK I would happily pay someone else to do the mod, but for now I'd just love to know how the air might be getting into the system in the first place. I might be able to attack the problem from that angle.
Any suggestions or opinions gratefully received.

[vanfox]

I read somewhere ...... the leak off pipes return excess fuel from the injector to the tank.
I also read somewhere..... air in the hi pressure pipes can actually be combustion gases getting past a worn injector.
A diagram of the injector would help to understand this. If I recall, the injection pressure opens a needle valve against compression pressure, the needle valve leaks, gas gets into the pipe.
Then again I could be totally mistaken.
If you have access to one new or good injector try swapping one out at a time to see if the situation changes.
This assumes you're not sucking air from the tank thru' running on empty and no fuel leaks on the supply side of the IP.
You may be able to reach the T piece in the return pipe by disconnecting the pipes from the filter head and carefully pulling them towards you.

[Aardvark]

Thanks for the input, mate. "the leak off pipes return excess fuel from the injector to the tank".
OK, sounds right. The injectors are fed with more fuel than they actually need and pass on the excess to the tank. A valve in the injector controls the point when the bypass begins. So a faulty injector/valve could cause the malfunction you describe. A spare injector (of the right type) would be dead handy for troubleshooting. Your second idea about sucking up air from an empty tank is unlikely. I always go for a full top-up when I get just below the quarter tank. I can't see any leaks between the tank and the filter housing.
As regards getting at the tee piece at the back of the rocker cover your idea might be worth a try. How do the connectors at the fuel filter top actually disconnect, and the connections to the tee piece?

[Keef]

Put some clear pipe between fuel filter and injection pump, if you can see bubbles in the fuel the air is from the fuel supply, if not then probably from injectors.

If it is from the fuel supply and your van has the push fit connectors I'd suspect them or the fuel filter housing. You can smother the connectors one by one in thick grease to find out which one is letting air in and don't forget the lift pump has them too.

I couldn't get to the back T when I did the leak off mod so I bought a small straight connector then took the pipe off No4, pushed the connector into it and extended it to No1 and moved the blank to No4.

[Aardvark]

"I couldn't get to the back T when I did the leak off mod so I bought a small straight connector then took the pipe off No4, pushed the connector into it and extended it to No1 and moved the blank to No4"

I was thinking of trying that approach a while ago and ordered a straight connector online. When it arrived it had such a tiny bore I was concerned that it wouldn't flow as much as the rubber return hose so I never tried to use it. Knowing nothing about injection I didn't know if there is much flow or just a trickle.

I'm still trying to work out how to get the damned plastic connectors to undo. The ones I can actually see are on the top of the fuel filter housing. Two little bumps that feel a little bit loose. Tried squeezing them together and pulling at the pipe but no go. Tried twisting like a bayonet fitting but no go. Trying some Googling but no luck yet. I'm confident that if I'm to heavy handed and break the fittings its game over for weeks until I can get replacements sent from UK.

[INTRANSIT]

When i did the leak off mod on mine i used a 2" piece of old fishing rod that was a tight push fit as a straight connector
cured the air problem had no problems with it., or you could try a airline connector from local pet shop.
should be a tight fit and just warm the return pipe with hot water before pushing it on , same thing makes it easier to remove the old rubber pipe.

[Keef]

I was thinking of trying that approach a while ago and ordered a straight connector online. When it arrived it had such a tiny bore I was concerned that it wouldn't flow as much as the rubber return hose so I never tried to use it. Knowing nothing about injection I didn't know if there is much flow or just a trickle.

The T has probably got a very similar bore and so has the connector on the injector so I can't see that there is any more restriction with your straight connector

I'm still trying to work out how to get the damned plastic connectors to undo. The ones I can actually see are on the top of the fuel filter housing. Two little bumps that feel a little bit loose. Tried squeezing them together and pulling at the pipe but no go. Tried twisting like a bayonet fitting but no go. Trying some Googling but no luck yet. I'm confident that if I'm to heavy handed and break the fittings its game over for weeks until I can get replacements sent from UK.

From memory it's just press the two bumps to release and pull the pipe out. I'm not near my van atm to confirm that though

[Jim Archer]

Thanks for the input, mate. "the leak off pipes return excess fuel from the injector to the tank".
OK, sounds right. The injectors are fed with more fuel than they actually need and pass on the excess to the tank. A valve in the injector controls the point when the bypass begins. So a faulty injector/valve could cause the malfunction you describe. A spare injector (of the right type) would be dead handy for troubleshooting. Your second idea about sucking up air from an empty tank is unlikely. I always go for a full top-up when I get just below the quarter tank. I can't see any leaks between the tank and the filter housing.
As regards getting at the tee piece at the back of the rocker cover your idea might be worth a try. How do the connectors at the fuel filter top actually disconnect, and the connections to the tee piece?

The 'leak-off' is from the fuel used to lubricate the pintle shaft, there is no bypass as such. The HP delivery to the injector relies on a consistant 'pop off' pressure to gaurantee injection timing and delivery. Any 'spill off' happens in the pump itself and is governed by openings in the spill sleeve around the HP piston moving relative to piston stroke under the governor action.

Jim

[Aardvark]

Thanks for the explanation Jim.
So the leak off is just a lubrication excess and probably not leaving the pump in any great pressure.

[fordrs726]

had same problems with 2 smileys put new injectors in problems gone tried the leak of mod did not work on mine only new injectors worked still got the 2 smileys no problems since 3 years ago

[Aardvark]

had same problems with 2 smileys put new injectors in problems gone tried the leak of mod did not work on mine only new injectors worked still got the 2 smileys no problems since 3 years ago

I will keep that (expensive) suggestion on my list. I have a French MOT coming up soon that might just take me off the road permanently due to rust. If it somehow passes I will be happy to throw more money at it to cure the problem. Meanwhile I just bleed the damned things before going on every journey and keep the rags and 17mm spanner in the door pocket ready to use.

[gotgcoalman]

Without reading back.
Are the leak off pipes sealing?

old ones tend to become brittle and no provide a decent seal.

Air could be caused by that and it's an easy diagnosis/fix.

[Aardvark]

Without reading back.
Are the leak off pipes sealing?

old ones tend to become brittle and no provide a decent seal.

Air could be caused by that and it's an easy diagnosis/fix.

I renewed them about three years ago. It might be worth doing again just to rule that one out. Thanks.

[Aardvark]

Update
Didn't manage to cure the problem but had to make another 350 mile trip to empty a house. Bled the injectors before setting off but had to do it again after about an hour on the motorway. Got about another half hour's driving in and it lost power again. Bleeding it helped a little but not much so had to abort the journey and return home. No load in the van, seemed to run OK (?) on the level or downhill but uphill was a nightmare. Down to fourth & third revving hard to keep moving. Tons of sooty black crap out the exhaust all the way. When I got home it just didn't want to stay running at all. This morning I tried another bleed session but no improvement at all. It seems to be running on only one or two pots and is making a loud chuffing noise back through the intake.
I think now may be the time to scrap it and cut my losses. A shame because I have recently spent a lot on new brakes and cabling, etc. to get the damned thing to start in the mornings. And there's over £200 worth of new body panels indoors waiting to be fitted. I'm stuck with taking it to a scrapper rather than keep tinkering with it. The law here means it can't be SORNed and the insurance has to be paid even if its a non-running heap of parts.

[derv23]

There's not a blockage in the fuel / air filter is there ?
I don't know prices or availability but could you not drop another lump in it ?

As you said it'd be a shame to get rid of it now with the work/money been put into it so far!

Good luck