fuel pump tone

[pulsarboby]

was listening to car running today and noticed the engine rpm dips slightly at certain points...seems to do it regularly to the point the engines about to stall.

when this happens the noise of the fuel pump changes also (goes quieter) has anyone else noticed this with their cars? as im wondering if its the pump or possible wiring prob

[aide]

shot in the dark here - but is your fuel cap on tightly - and is the seal ok.
if it's left off accidentially - esp with less fuel in the car - the pump labours to keep the pressure up.
hth

[pulsarboby]

yep thats on there tight
it seems fine when its cold but its when the engines up to temp
will see how it goes as engines all new and nowhere near run in yet
cheers for the input though fella

[ridds]

I would stop driving it.

Fuel pump tone changing means there is a change in demand or fuel supply. This could be a failing pump, blocked filter, blocked lines etc.

That combined with the change in engine speed all adds up to possible fuel starvation to your new engine with potentially catastrophic consequences!!

[pulsarboby]

thanks
it only does it at idle though
andy at apm test drove the car before i collected it and said everything was fine and ive only done around 10 miles in it since collecting it.

are the pumps in these located in tank or outside as ive not looked yet?
also does anyone know what pumps are fitted as in lph?
il put a new filter on it first of all though as a precautionary measure then check voltage etc to pump to make sure its recieving correct voltage and there are no earthing issues
plus im not driving it over 3k rpm whilst its being run in

[Tang Soo Tim]

Pump and filter in passenger rear wheel arch



Pump at the base filter at the top i believe

[pulsarboby]

thanks
il take a looky see

[GT6k]

Just to be picky, that's the fuel filter and carbon cannister behind it in the wheelarch whilst the fuel pump is on the bottom chassis rail inbetween the lower wishbone arms. (Sorry if i am teaching my grandmother to suck eggs)

Other possiblities for the hunting might be
- the return line is slow so what you are hearing is resistance to returning un used fuel and of course under power very much less fuel is having to be returned.
- or as the engine nears stall the voltage drops and that slows the pump before the ECU picks the revs back up then the voltage increases and the pump speeds up.

[pulsarboby]

yeah thats good info there thanks
ive checked voltage to pump and all is good

so im gonna plump with a problem with fuel return pipe as when you come off throttle she cackles, pops and bangs quite loudly which from my experience as you rightly said could be a sign of overfuelling

[Tanguero]

pulsarboby said:

so im gonna plump with a problem with fuel return pipe as when you come off throttle she cackles, pops and bangs quite loudly which from my experience as you rightly said could be a sign of overfuelling

Pops and bangs on the overrun is perfectly normal for these engines and won't be anything to do with it. I think it highly unlikely that the return line is the problem either as there are no restrictions in it, it's just a straight through pipe. It would be more likely to be the pressure regulator on the back of the fuel rail, if you are convinced it is an outlet restriction. However a pump feed or electrical issue is most likely.

The pump is a Bosch 044 if you need to replace it.

[pulsarboby]

cheers
the pump feed is spot on and getting full voltage
not checked pressure reg yet
but i have a good 044 i removed from a gtir so think il slap that on to eliminate a pump fault before i go any further

[Tanguero]

If it still does do it with the fuel cap off then regulator is a good bet. The usual problem though is a tank venting one - often the carbon canister blocked (or full of petrol!!) or the purge valve sticking.

Edited by Tanguero on Friday 1st June 16:09

[pulsarboby]

ok thanks
il check those bits before i do the pump
hopefully then prob solved