Fuel Pump Primeing

[wah 0]

Am I right in thinking that I should here the fuel pump prime on the first turn of the ignition !!, I have had the pump relay apart and nothing happens to it until I try to start the car and then relay closes, am I miss understanding it or am I right ??

 

 

Si

[pug_ham 245 3 Cars]

Try a search, sometimes they do & sometimes they don't.

 

Never the same two starts in a row imo.

 

Graham.

[wah 0]

Right still no further on with this bought another pump relay and it's still the same, if I maually depress the relay in so it primes the pump the car will start straight away, how ever if I dont as you can imagine it takes an age to start, I think it's only ever primed twice so thinking there maybe a short to the relay somewhere.

 

Any help is grateful

[Anthony 1,003]

Sounds like to me you've a knackered one-way valve in the fuel pump, as even without priming, it should still start pretty much straightaway unless it's been sat for a long time. As Graham said, sometimes they prime and sometimes they don't, and I don't think that it's directly related to the tachymetric relay itself.

[wah 0]

When you say a long time it does sit for upto a week at a time as it's a project car that I'm doing, now does that still mean that if the one-way valve was ok it would still fire up pretty much straight away ?, how does tha pump know when and when not to prime ?

[wah 0]

Right the pump has now decided to start primeing, however on the second turn of the key when it primes is it supposed to stop once pressure is built ? as mine just continues to prime thus flooding the car !!

[rescue dude 0]

Do you have another fuel pressure regulator?

 

I may be wrong but if the regulator is faulty the system wont reach the pressure needed and therefore the pump will continue to prime, trying to reach the pressure needed for it to stop.

 

Not sure these can be cleaned out but its worth taking it off and having a look.

[wah 0]

Answer to that one is no

 

I guess it's on with finding another regulator now to see if it's that

[timb1046 1]

would the regulator realy effect it? theres nothing from the regulator iirc to the ECU to tell it to stop the priming. mine used to prime all the time, but this shouldnt flood the engine as the injectors wont be firing. so whilst priming any extra fuel just goes back along the return pipe and into the tank. this is my understanding anyway.

[wah 0]

On looking at the regulator it seems to have been changed from the original to this !!

 

 

[welshpug 1,737]

that's an FSE adjustable fuel pressure regulator, unfortunately not the most consistent of devices, IMO you need to source a good original item to replace that.

 

just a note, the fuel pump can run flat out all the time, but it will NOT flood, it can only flood if the injectors inject too much fuel.

 

As timb1046 said any excess fuel goes straight back to the fuel tank.

[wah 0]

Cheers Welshpug had this feeling you were going to say it was an FSE, so why has the pump going from not primeing on the key to full out on ???

[Anthony 1,003]

Faulty tachymetric (fuel pump) relay would be my suspicion

[wah 0]

I have just replaced this item

[Anthony 1,003]

I have just replaced this item

And the pump kept running with ignition on (but engine not running) on both the old one and new one?

 

The tachymetric relay should really only activate the fuel pump for one of two reasons - either it gets a pulse back from the coil (ie engine running/cranking) or because the starter solenoid is engaged (ie engine cranking / trying to crank). I don't fully understand the priming behaviour and in particular how it does it, but I believe that it's triggered by a single coil pulse on ignition on.

 

What I can say however, is that it is a completely dumb system - there is no fuel pressure sensor as such, so it won't be priming continuously trying to bring the system upto pressure. If it primes at all (and as said before, this seems to be very random) then you just get the pump running for a second or two, purely to "top up" the fuel pressure - it won't prime an empty fuel system for example without cranking the engine over to force the pump to run.

 

As has also been said, even if the pump was running continuously, it would just pump fuel round and round, and would not flood the engine or inject any fuel whatsoever. Injection is handled seperately, although the injectors are powered from the fuel pump relay (and the ECU then grounds the injector to inject fuel). If your engine is flooding with fuel without turning over, then you need to investigate why!