Mk7 Fuel pressure 4000Kpa on starting

[Bryce1_1]

Hi All,

I have read a heap of post but I’m still unsure where to look.

So recently I got a van running after it was found in a unknown condition after the purchase of a property.

I was driving around in 1st gear for 5mins and stalled it when I went to second. Since then I have been unable to get it to start. It turns over but no ignition. Forscan says the fuel pressure is 4000kpa with the engine turning over. If anyone could provide some guidance on where to be begin looking it would be greatly appreciated.

Thanks

[v8dave]

Check the sync signal.

The ecu reads both the crank speed/position and the cam position.
If the cranking speed is too low or the cam and crank are not syncronised the injection will not operate.

[knobby1]

Hi All,

I have read a heap of post but I’m still unsure where to look.

So recently I got a van running after it was found in a unknown condition after the purchase of a property.

I was driving around in 1st gear for 5mins and stalled it when I went to second. Since then I have been unable to get it to start. It turns over but no ignition. Forscan says the fuel pressure is 4000kpa with the engine turning over. If anyone could provide some guidance on where to be begin looking it would be greatly appreciated.

Thanks

What v8dave said....also, did Forscan throw up any fault codes..?? If fuel pressure is only 4000kpa you may have a blown PRV. The PCM will not allow the injectors to operate if the fuel pressure is not within it's specified range. If indeed the PRV is blown, it will be a duff SCV causing it.

Lord Knobrot

[v8dave]

There is the possibility that the fuel level in the tank is too low.
Or that the fuel filter has clogged up.
Or there is an air leak in the fuel lines, the injection pump sucks fuel through the filter from the tank and air is easier to suck up than fuel.

[knobby1]

There is the possibility that the fuel level in the tank is too low.
Or that the fuel filter has clogged up.
Or there is an air leak in the fuel lines, the injection pump sucks fuel through the filter from the tank and air is easier to suck up than fuel.

Good points Sir..

Lord Knobrot

[Bryce1_1]

I have changed the fuel filter with a new one. There is about half a tank of new diesel in the tank.

Is there any way of testing the SCV without replacing it first?

Here is a photo of some Forscan values during cranking:

E8EA2505-358E-45D4-A98A-3A7921528C36.jpeg

[knobby1]

I have changed the fuel filter with a new one. There is about half a tank of new diesel in the tank.

Is there any way of testing the SCV without replacing it first?

Here is a photo of some Forscan values during cranking:

E8EA2505-358E-45D4-A98A-3A7921528C36.jpeg

Did you brim the filter with fresh fuel before fitting..?? If not the pump may be full of air...Mk7's are self priming but only if they can start/run.

Your "desired" fuel rail pressure is 38125kpa (~5530psi) during cranking...however, your "actual" fuel rail pressure is only 1810kpa (~262psi)...so she's never going to run. Pop the PRV out of the rail and see if it's in pieces...

The SCV is just a variable voltage solenoid, there's a little spring loaded metering piston inside...sometimes the bore can get scored and the piston will often stick causing hysteresis, which in turn causes the hunting. If the piston sticks in the "open" position, you'll have full pump pressure all the time and this is what blows the PRV. The PRV is there to protect the pump, lines and injectors from stupid pressures... which can easily damage them if too high. Even with just normal running pressures we're talking up to ~29-30,000psi at full noise....the pump is quite capable of delivering much more than that....the two valves and injectors are not.

Lord Knobrot

[Bryce1_1]

Thanks for your great reply Knobby.

I have pulled the SCV and the PRV. When the SCV is plugged in, it vibrates fairly hard for around 30seconds before stopping. Also it seems to only move about 5mm with the ignition on but not cranking. I have attached a photo of the PRV, I’m not sure if that’s what you mean by in pieces but that’s how it came apart.

EC06688E-C923-4D2A-93EE-894EB8C7760C.jpeg

[knobby1]

Thanks for your great reply Knobby.

I have attached a photo of the PRV, I’m not sure if that’s what you mean by in pieces but that’s how it came apart.

EC06688E-C923-4D2A-93EE-894EB8C7760C.jpeg

LOL... That'll do it every time....your PRV is fugged, it should come out in one piece, hence the lack of fuel pressure.

I'd recommend replacing them both, then a set of learns....should see you sorted.

Lord Knobrot

[Bryce1_1]

So I have finally received the parts and replaced them. When I try to do the pump learns it says the vehicle needs to be running. I tried to start it up but now I am only able to get 800kPa fuel rail pressure where as before I could get up to 4000kPa pressure before I'm assuming the PRV would relieve the pressure.

Any ideas on where to go from here?