Fuel pump popping noise

[fla 9]

Strange one here - sometimes (and there seems to be no discernible pattern to this) on cranking the engine there will be a pop from the side of the car and the car then just continues to crank for a while - maybe about 4 or 5 more turns. Sounds as if the fuel pump momentarily loses power and shuts off only to start up again. The car then fires and runs normally.

 

I installed a check valve about 12 months ago in the fuel tank to sort the 'long cranking when warm problem' so i'm not sure if its related. Not really sure what to look for, i'm thinking of checking the wiring to the fuel pump for breaks, maybe remove the check valve, cant think of anything else tbh

 

Any suggestions???

[fendervg 33]

Sounds like there could be an air lock in the system that then clears - I'd have a good look at the pipes around the fuel filterand change the filter if it hasn't been done recently. Is there any smell of fuel during this?

[fla 9]

Good call Fender, will do. Changed the filter about 10 years back so perhaps worth changing again

[vw rule 19]

Good call Fender, will do. Changed the filter about 10 years back so perhaps worth changing again

 

I'd definitely get the fuel filter changed especially if it hasn't been replaced in 10 years, as the paper/mesh filter itself inside will possibly break up, and can lodge partially obstructing the fuel outlet, which is when you may hear the popping/rattling noise, as it moves around and then suddenly clears.

 

Ideally you should replace your fuel filter once a year, or every 12k to 15k miles, Main Dealerships change them possibly every 25k or 30k, but that's on a company car that's used regularly and will soon do that mileage.

On our Corrado's it won't hurt replacing the fuel filter every 6k or 8k or once a year, especially if it's not used regularly.

 

Relay with number 167 stamped on it is for the fuel pump, the main live feed wire is red/yellow which also goes to fuel pump.

 

You should have constant 12v power to fuel relay and fuel pump, when cranking engine via key plus once engine starts.

Also you need correct fuel pressure in fuel return line from injector rail to fuel tank,

basically should be like a constant syphon effect, helped by the fuel pressure regulator which should maintain a pressure in return line back to fuel tank,

if you get a break in this syphon flow it'll effect starting engine.

 

Crank engine over you should be able to feel the fuel relay click on, and then off once you switch ignition off.

If you hear/feel the relay going mad and clicking on/off when cranking engine, then clearly something is wrong with your electronics.

 

 

Hope this helps

 

Si

Edited October 12, 2019 by vw rule

[Bauhaus 3]

I'd definitely get the fuel filter changed especially if it hasn't been replaced in 10 years, as the paper/mesh filter itself inside will possibly break up, and can lodge partially obstructing the fuel outlet, which is when you may hear the popping/rattling noise, as it moves around and then suddenly clears.

 

Ideally you should replace your fuel filter once a year, or every 12k to 15k miles, Main Dealerships change them possibly every 25k or 30k, but that's on a company car that's used regularly and will soon do that mileage.

On our Corrado's it won't hurt replacing the fuel filter every 6k or 8k or once a year, especially if it's not used regularly.

 

Relay with number 167 stamped on it is for the fuel pump, the main live feed wire is red/yellow which also goes to fuel pump.

 

You should have constant 12v power to fuel relay and fuel pump, when cranking engine via key plus once engine starts.

Also you need correct fuel pressure in fuel return line from injector rail to fuel tank,

basically should be like a constant syphon effect, helped by the fuel pressure regulator which should maintain a pressure in return line back to fuel tank,

if you get a break in this syphon flow it'll effect starting engine.

 

Crank engine over you should be able to feel the fuel relay click on, and then off once you switch ignition off.

If you hear/feel the relay going mad and clicking on/off when cranking engine, then clearly something is wrong with your electronics.

 

 

Hope this helps

 

Si

 

There is some slight misinformation here; there should be hardly any fuel pressure to speak of in the return lines.

Pressure is the resistance to flow, (higher the pressure the slower the fuel flow which is not what’s needed in the return line), so if there is any pressure in the return line you may have a serious blockage in the fuel tank vent which could be the popping sound of it releasing pressure.

[fla 9]

Well the fuel filter change has made a big difference - no sluggish starting and so far no popping noises again!

Got the wrong size from Bosch which according to their part numbers was correct. Returned it and bought one from GSF (Mann) fits perfectly.

 

Used some silicone grease on the clips.

 

Longest part was locating the trolley jack in the right place whilst having space for the stand AND having clear access.

[fendervg 33]

Well the fuel filter change has made a big difference - no sluggish starting and so far no popping noises again!

Got the wrong size from Bosch which according to their part numbers was correct. Returned it and bought one from GSF (Mann) fits perfectly.

 

Used some silicone grease on the clips.

 

Longest part was locating the trolley jack in the right place whilst having space for the stand AND having clear access.

 

Good to hear - hopefully that will have sorted it.

 

I'm always nervous using the jack and worried about crushing some part. For the reat I lift under the beam at the centre and then use axle stands both sides.