How to check the fuel pressure regulator and coolant sensors? Hot starting

[_Matt_ 32]

Hi all,

 

I've noticed my VR is more difficult to start when warmed up. When cold and left for days it cranks a 2/3 times and fires up. After a longer drive it doesn't start so easily and I instinctively give it a bit of throttle to get it going.

 

 

I've read on here that it is a bit of quirk of the VR and also read about checking the FPR and blue coolant sensor. How do I check these? My mechanic put his VAG-COM on it last week but nothing was listed.

 

Cheers

Matt

[Jim Bowen 1]

Mine used to do that, i changed the fuel pump relay which fixed it. But you never know with these cars if the same thing causes the same problems.

[_Matt_ 32]

Oh yes I remember reading your reply on one of the posts - the relay running hotter if I recall. This is something else to investigate - but first I need to find them. I've only had the car 3 weeks but love to tinker :)

[Jim Bowen 1]

They are all by the fusebox, might be worth just taking it out and giving it a clean or a wiggle :lol:

[fla 9]

fuel pump relay is 167 (or sometimes numbered 67).

Yes mine does this too - always makes you think whether it will start or not!

I've changed the blue temp sensor, crank sensor, cam sensor, put a check valve in the fuel tank, just need to change the fuel pressure regulator now but it still behaves the same way.

[_Matt_ 32]

Cheers - is it worth cleaning electrical contacts with Electrical Contact cleaner (the stuff in a aerosol can)?

[fendervg 33]

Worth checking the FPR - there is a small allen-head nipple on the front of the fuel rail on the left, near where the flexi-hoses for feed and return join, you can connect a pressure gauge here to test it. Be careful undoing it as there may be a fair bit of residual pressure there.

 

The fuel pressure should be 3.5 bar with the pump running, and rise to 4 bar (fuel pump nominal pressure) when you disconnect the small vacuum hose feed on the FPR.

 

With the engine turned off, it should keep a good residual pressure and still show >3 bar after half an hour or so.

 

A few of us on here have fitted a small non-return valve on the feed hose at the pump end in the fuel tank and this has sorted warm starting issues. I'd also check the hall sender (either part of the distributor, or in the side of the head near the coil pack) as they are also known to cause hot starting problems sometimes.