Mk7 2.4 transit hot start problem

[Yz Garry]

I had put new starter motor in the van around 6 months ago because I had the same thing hot start problem but the starter sorted so when van start playing up again the 1st thing I done was change starter under warranty but it made no difference

[DanMK7uk]

Remember you saying, was for kopon as he mentioned his.

[Yz Garry]

It turns over just don’t fire up

[Burn2]

Battery are good? ( Connexion too like ground? )
When you try to start the engine when hot does the voltage go really low when starting?

[Kopon]

I have changed leak off seals checked fuel filter housing for cracks can’t see any checked all fuel lines round engine can’t see anything losing the will to live now.

You won't see any air leaks and fuel doesn't leak out as the system is under a slight vacuum when the engine is running, there in no pressure in the inlet side of the fuel system on a Euro-4, they don't have an "in-tank pump" like the Euro-5's.

Lord Knobrot

Just returning to this thread as it's the most relevant for me. In my case, the hot start problem appears to have been fairly well resolved by replacing the starter. I'm not sure if it reduced the current draw or perhaps increased the cranking speed but, either way, hot start is greatly improved. However, I'm now concentrating on poor cold starting, mainly due to only driving the van at weekends and finding a half full fuel filter.
Knobby, your understanding of the fuel system for the Euro4 is what intrigues me. Can you explain why the fuel system is under a slight vacuum when the engine is running? Isn't there a mechanical lift pump to suck fuel from the tank = vacuum ok. But, thereafter the fuel is pushed to the filter and on to the HP pump = pressure? Or is the HP pump drawing the fuel from the tank via the filter? Anyway, I'm struggling to understand how air ingress would deplete the contents of the filter regardless of the source or location of the defective part.
Thanks.

[knobby1]

I have changed leak off seals checked fuel filter housing for cracks can’t see any checked all fuel lines round engine can’t see anything losing the will to live now.

You won't see any air leaks and fuel doesn't leak out as the system is under a slight vacuum when the engine is running, there in no pressure in the inlet side of the fuel system on a Euro-4, they don't have an "in-tank pump" like the Euro-5's.

Lord Knobrot

Just returning to this thread as it's the most relevant for me. In my case, the hot start problem appears to have been fairly well resolved by replacing the starter. I'm not sure if it reduced the current draw or perhaps increased the cranking speed but, either way, hot start is greatly improved. However, I'm now concentrating on poor cold starting, mainly due to only driving the van at weekends and finding a half full fuel filter.
Knobby, your understanding of the fuel system for the Euro4 is what intrigues me. Can you explain why the fuel system is under a slight vacuum when the engine is running? Isn't there a mechanical lift pump to suck fuel from the tank = vacuum ok. But, thereafter the fuel is pushed to the filter and on to the HP pump = pressure? Or is the HP pump drawing the fuel from the tank via the filter? Anyway, I'm struggling to understand how air ingress would deplete the contents of the filter regardless of the source or location of the defective part.
Thanks.

As mentioned, there is a slight vacuum on the low pressure side of the fuel supply from tank through the filter to pump....from the pump to injectors is high pressure. Yes, the HP pump draws the fuel from the tank through the filter, hence the slight vacuum. he leak-back lines are part of the low side.

The internals of the filter are sealed and any air ingress between the filter and the engine in the low pressure side (downstream of the filter) will have fuel slowly siphoning back to tank and filling the filter with air.

Lord Knobrot (Smithy)

[Kopon]

OK.
But I can't get my head around how the syphoning can happen as none of the pipes attached to the filter head actually protrude into the filter body? When I remove the filter the fuel level in it can be around half full which is a complete mystery to me.
In another thread I have posted some images of live Forscan data showing extremely high FRP, (92000 kPa & 93750 desired at 3781 rpm) I'm now wondering if some of this pressure could escape back through the system and possibly force fuel out of the filter. Just a thought.
So just to clarify:
There is no LP pump in the tank and no mechanical lift pump on the engine?

[knobby1]

OK.
But I can't get my head around how the syphoning can happen as none of the pipes attached to the filter head actually protrude into the filter body? When I remove the filter the fuel level in it can be around half full which is a complete mystery to me.
In another thread I have posted some images of live Forscan data showing extremely high FRP, (92000 kPa & 93750 desired at 3781 rpm) I'm now wondering if some of this pressure could escape back through the system and possibly force fuel out of the filter. Just a thought.
So just to clarify:
There is no LP pump in the tank and no mechanical lift pump on the engine?

The filter itself just continues the flow of the pipes when it is fitted, the way it seals inside the housing just makes the filter one of the pipes...just believe that it does. What you're experiencing is very common ragarding the filter being emptied.

No lift pump other than the HP pump which does both on a Euro-4...the Euro-5 has a lift pump in the tank. The pressure does not escape back through the low side. There is a return to tank via the leak-back lines from the injectors though.

Lord Knobrot (Smithy)

[Kopon]

Thanks, Knobby.
I do understand now that there is no pump between tank and filter.
However, I remain baffled by how quickly the fuel is lowered in the filter if only due to air ingress.
In any event, I need to address the high FRP readings as a priority. Presumably a change of PRV to begin with?

[T350camper]

Knobby is bang-on with his description that you should think of the filter as one of the inlet pipes (which it is). If there is the slightest imperfection between the filter seal and housing, you would think it should leak fuel, but due to the slight depression it tends not to and the system self bleeds minor air bubbles as you drive. But when you switch off and the mechanical pump on the engine stops, then gravity takes over. Air weeps into the filter and the heavier fuel makes its way back to the tank.

[knobby1]

Knobby is bang-on with his description that you should think of the filter as one of the inlet pipes (which it is). If there is the slightest imperfection between the filter seal and housing, you would think it should leak fuel, but due to the slight depression it tends not to and the system self bleeds minor air bubbles as you drive. But when you switch off and the mechanical pump on the engine stops, then gravity takes over. Air weeps into the filter and the heavier fuel makes its way back to the tank.

Exactly this ^^

Lord Knobrot (Smithy)

[Kopon]

Yes, I get that now. Thanks.
The rubber seal on the filter is what effectively makes it become part of the feed pipe so, to all intents and purposes, it's just like a large bulge on the pipe. That being the case, I guess the drain back is more likely to be via the feed pipe rather than the return pipe?

[knobby1]

Yes, I get that now. Thanks.
The rubber seal on the filter is what effectively makes it become part of the feed pipe so, to all intents and purposes, it's just like a large bulge on the pipe. That being the case, I guess the drain back is more likely to be via the feed pipe rather than the return pipe?

For the filter to be losing fuel or siphoning back to tank....the air ingress must be downstream of the filter, cracked filter head, fittings on the supply line from filter to hp pump, injector leak-back lines and their O-rings.

Lord Knobrot (Smithy)

[Kopon]

Without wishing to be pedantic and I know you generally don't do typos but my understanding of the sequence would be that the air ingress must be UPstream of the filter?

[Kopon]

I found this diagram which appears to be a fairly decent depiction of the Euro4 fuel system.
If so, it may help others to understand the workings. However, even if it's correct for my van, it may not hold true for other models?

HPCR Fuel System.jpg