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Model specific boards => Golf mk2 => Topic started by: maxp on 24 May 2009, 17:02

Title: Bubbles in fuel return line
Post by: maxp on 24 May 2009, 17:02

Have been having problems starting the car when hot.

Looked under the car, found out there were quite a few bubbles in the fuel return line.

On priming the pump (1st click) i see more bubbles appearing,

There is a slight smell of petrol when the car does finally start when it's hot (took about 8 tries this afternoon- but once started is fine)

Im betting in on it being a faulty fuel pressure regulator.

Does anyone agree with this or can offer insight?

Title: Re: Bubbles in fuel return line
Post by: mattkh on 24 May 2009, 21:40

Hi
Does the fuel pressure regulator on the fuel rail have a vacuum pipe ?
If it does, take it off, have a rag handy and check to see if it spurts any fuel. If it does then the diaphragm is faulty and may be the cause of the air bubbles.

Title: Re: Bubbles in fuel return line
Post by: maxp on 25 May 2009, 13:17

Just tried it, vacuum is sucking fine and nothing was coming out.

Argh any ideas? Maybe it could be blocked or a have a split in a seal?

Title: Re: Bubbles in fuel return line
Post by: rubjonny on 26 May 2009, 10:41

has the ecu temp sensor been replaced recently? if not go buy a new one from VW.  check you get a spark when hot, the fuel rail and fpr dont tend to go wrong.

Title: Re: Bubbles in fuel return line
Post by: maxp on 26 May 2009, 11:31

Yes it has-ish (few months). How would that affect bubbles in the fuel line though?

Title: Re: Bubbles in fuel return line
Post by: rubjonny on 26 May 2009, 12:06

my thinking was the bubbles arnt anything to worry about and the cold start is being caused by something else ;)
check over all your fuel lines for cracking and splits, especially the fuel rail ones at the ends, plus make sure you have no leaks.

Title: Re: Bubbles in fuel return line
Post by: maxp on 26 May 2009, 13:23

There are quite a few of them! Say 1 cm of solid bubble for every 10cm of petrol. Shouldnt a fpr totally remove all these bubbles as they would make the circuit pressire too low?

Title: Re: Bubbles in fuel return line
Post by: rubjonny on 26 May 2009, 14:39

youre only seeing fuel that has been returned to the tank, if there isnt enough pressure to open the fpr it wont send anything back to the tank see.

Title: Re: Bubbles in fuel return line
Post by: maxp on 26 May 2009, 14:48

ah so it only really matters that the supply to the rail has good pressure then.

Title: Re: Bubbles in fuel return line
Post by: rubjonny on 26 May 2009, 15:51

exactly! not saying these bubbles are definitly not a problem, but i dont think they are.  maybe you have a loose fuel line somewhere introducing air into the system?  as i say, check you get a good spark when the engine is cranked over hot.