Car consumes way too much petrol

[Brian Moseti]

Update on return pipe mod.

The return pipe, I had fitted on my r4 served me quite well, but only on level ground or going downhill. Got amazing fuel consumption rates, but I had to get rid of it because once the fuel in the tank dropped below half, I could not drive uphill. I am not sure why, and at one time, I had to drive up a slope in reverse--which almost killed my clutch plate --- but after getting rid of the return system, I can now drive up the steepest of hills on just 2 litres of fuel.

 

[André4Renaults]

Not being able to drive uphill suggests a lack of pressure, as opposed to too much of it! The pump should be able to draw fuel from the tank, regardless of the gradient. I still think there's a fault at the pump which needs investigating, rather than the fuel return pips mechanism. As you can drive UP hill in reverse with a minimal amount of fuel in the tank means that the fuel lines are in good order, but that the pump pressure is insufficient and can only draw fuel when there's a "head" of fuel in the tank, to give it sufficient pressure, regardless of the work of the pump.

 

[AdamWilkes]

I agree - but was the fuel return pipe unrestricted? That would lead to the fuel taking the easiest route , which would be back down the pipes to the tank, with very little being pumped into the carb which is uphill (especially when facing uphill) and through a restriction (the float chamber valve).

Drawings I have seen include a small restriction on the return circuit to avoid this (increasing the pressure in the pipe to the carb slightly); as standard, my F6 had no return pipe. I tried fitting a return pipe with a 1mm restriction to keep the fuel cooler (less fuel standing still over a hot engine), but I had trouble with fuel draining out of the pipes making starting after a few days standing very slow - the fuel had evaporated from the float chamber & the pipes emptied. One-way valves were tried but were rubbish - am unsure if the fuel pump includes a one-way valve? I now use an additional electric fuel pump which turns on with the ignition & cuts out when the engine starts, just to make sure the float chamber is full before starting. I probably have an fuel issue too!

 

[Brian Moseti]

@AdamWilkes.... It's true, I was running the pipes unrestricted, but now I am just too tired to keep on with the experiment, and since the car runs well without the return, I think I will stick to stock-mode. It is also great to know of your electric pump option, in case I ever change my mind. My only other problem now is that I get a lot of banging noises in the rear,, which disappear when I have passengers or heavy luggage at the back... When I got the car, it was raised higher at the back than at the front, and I suspect this could be causing the banging when the load is lighter... but not sure. Have you experienced this? Do I need to reduce the rear clearance?

 

[AdamWilkes]

Have a look at the page: https://www.renault4.co.uk/tech-ride-heights.htm

Banging noise is something loose! Probably exhaust or suspension stuff about to fall off. Whatever it is I think it is important to take a look !

I've not had such a thing with a Renault 4 but with a Citroen Visa, one rear wheel (complete with suspension arm) was about to fall off. I think the handbrake cable was doing a good job of keeping the wheel on when the rust gave way........