I am almost at the end of a Sylva Vectis build, the problem I have is getting the engine running right. Three years ago we decided to go for one last run in the MGF when the engine started to falter so decided to sort the problem when it was in the Vectis thinking it would be easier to solve due to improved engine access.

Fast forward to last spring and started to suspect the fuel pressure, i bought an inline fuel pressure gauge, the result being no pressure what so ever, the engine did start probably after 6 or 7 attempts but then very poor idle and sooty plugs.

I bought a new fuel pressure regulator and that seemed to solve the problem, fuel pressure was around 3 bar and over three short trips performance was very good. On the fourth trip (around 3 miles) the engine started to hesitate again and it didn't idle well.

I didn't touch it over the summer but looked at it over the last couple of weeks, the fuel pressure was zero again so adapting the inline fuel pressure gauge (blocking one end) and connecting it before the fuel rail the fuel pressure went from around 40 psi down to zero but over a period of 24 hrs.

Again connecting the gauge on the return pipe just after the fuel rail /injectors and on the return just before the tank gave the same results 40 psi disappearing over 24 hr period.

The fuel coming out of the return pipe to the tank looks to be coming out at a fair old rate but of course this is not measured.

I don't have the technical know how and do not understand where the system is losing pressure, i'm thinking it is the pump as the pressure is holding around the system after the pump and on the return just before the pump but at the same time can not get my head around the fact that if the fuel is returning into the tank how does the system get the required pressure.

The fact that the engine seemed to run well after fitting the new fuel pressure regulator and then after arout 6 -7 mile started playing up confuses me.

Can anyone offer any advice please

many thanks

Glynn

Have you verified the tank is properly vented?
If not vented, vacuum created on tank may lead to fuel starvation of the pump for what I can understand.
There´s more knowledgeable people here that may provide better insight.
AA

I think you are saying if you leave the engine not running, the pressure drops? That is normal, pressure will slowly be lost as the system is not designed to seal itself when not in use. Probably lost via the pump, or the regulator to the return though dribbling injectors are a possibility. But it sounds like the pressure drop is very slow. More useful is if the pressure drops very quickly once shut off.

Sooty plugs implies rich mixture.
But have you tried swapping fuel pumps to see if that is the issue? My car uses a gold intank pump, and I discovered it wasn't well and was only producing 3 bar of pressure (before the regulator which is a 3.5 bar one now). So a swap fixed that.

If you had fuel pump issues or excessive leak back when the engine the first symptom would bean abnormally long cranking time at a cold start, the normally acceptable leakdown is anything better than from working pressure to zero in 30 minutes. As Cliffhanger pointed out black fluffy sooty deposits on the spark plugs indicate an over rich mixture -- too much.

It would be good to know if the system is going closed loop and what temperature the MEMS ECU is reading from the CTS unfortunately the MGF unlike the later TF- is pre OBD2 so there are very few lower cost scantools that will talk to the ECU.

As mention by Angel a lack of tank venting could be the issue but if the same fault was present on the donor then it could be down to a heat affected electrical component the coil or crankshaft sensor, also check the two coolant sensors are correct connected not swapped over.

how old is the fuel in the tank?

As BT suggests black plugs are caused by running too rich , check or even replace the coolant temperature sensor and check the wiring continuity between the sensor and the ECU for broken wiring . Also check for air leaks in the inlet manifold area hoses etc .

Thanks for the feedback, I really appreciate it

I will check the ECU wiring etc, it is in the back of my mind if I cut too many wires in the early stages of the build, although I was very careful at the time

The fuel is a couple of weeks old

The tank is well vented

I agree, the sooty plugs indicate rich mixture but don't understand why the fuel pressure gauge indicates zero when the engine is running, I would think the pressure would be excessive.

The car performed really well for a short while when the fuel pressure regulator was changed, then suddenly reverted back to the same old problem.... very confusing

Think i'll change the pump, i did remove it yesterday and could not see anything obvious but if i change it then that will eliminate that possibility.

Thanks again

Glynn

Keep us posted, it may well help someone else in the future.Hope you get it sorted.