Electric fuel pump

Are you sure it is the pump you can hear?

Modern fuel pumps run with a continuous whirr, the excess fuel is continually pumped back to the tank to keep the whole lot cool.

mrcheerful

THey "should" stop when they reach a preset pressure.

Oh poo, now I've got to find out why my car is ticking as well as running rough. :-)

Thanks for the info. I'll get out there and lift the back seat and have a listen.

As a rule that's true; full flow is delivered to the engine, then the excess (not injected) passes through the pressure relief valve back to the tank. Some more modern systems have the regulator at the tank end instead; the pump still runs continuously, but most just circulates round the tank with only the required amound feeding down the pipe to the engine (this reduces heating of the fuel, and consequent emissions of vapour). In both cases the electric pumps run continuously.

However, some very modern vehicles do use a "demand controlled" system where the pump drive is closed-loop controlled to maintain the desired pressure, with no spill return at all. This is still pretty rare, and normally the pump should run at a steady low rate rather than switching on and off (unless the controller has been badly set up...)

Tony

Not on generic pumps. Some systems prime the pump for two seconds on IGN II then cut it (to bring the fuel rail to pressure) then will only run again once cranking and the engine is running. They will then run constantly with excess fuel being returned to the tank, only stopping if the engine does.

I think he meant the old SU pumps, pre return type systems. As found in minis, mg etc.

mrcheerful

Not on an EFI system.

Fair play to him in that case :)

Well yes, but not used on BMW 318i. Or any car within recent memory. ;-)

Sitting in the car in the quiet of the early hours of the morning and hearing the ticking it was exactly like that of an old SU pump. Maybe due to the time of day, it didn't even occur to me that pump technology must have moved on a bit by now. Know I'm really puzzled as to what it could have been.

What cars are these Tony, just for curiosity?

BMWs do seem to tick, about once every 10 seconds or so, but from behind the dash. I've never found anyone who knows what it is. The tick-tick-tick------tick-----tick-------------------tick of the old SU type pumps I've not heard of in a BMW. Could it be a fuel line tapping against the bodywork? Maybe the PO replaced the fule pump with a Mini one?!

Been having a think and I may have sussed it. I was sitting in the car putting an address into the Sat Nav. I've never heard it before but I think it might have been the Sat Navs DVD drive in the boot. A lot of noise for a DVD drive to make but it is bolted to the metal panel under the parcel shelf. I'll get out there and experiment the next time I'm up late.

To the best of my knowledge SU never made a high pressure pump needed for fuel injection. Indeed later BL vehicles still using SU carbs didn't use the SU ticking pump. By that time they used a flow and return system to help prevent fuel evaporation. And the SU pump wasn't designed to run continuously.