Intermittent Start Problem - Help!

[matty james]

also im sure your fuel pressure drops alot once u turn your engine off

[ndxturbo]

also im sure your fuel pressure drops alot once u turn your engine off

Correct me if I'm wrong, but from the research I've done, apparently when you turn the engine off, fuel pressure will slowly decrease rather than drop all together, so that restarting the engine is made easier?  I don't know if you're allowed to post links here so apologies if this doesn't work http://www.agcoauto.com/content/news/p2_articleid/195 but if you read this and see the pictures hopefully you'll see what I'm getting at. On the image on that page it's called an anti-drain back valve and i've seen it called a check valve on other web pages also, apparently if this is faulty then it can cause extended crank issues due to the fact that fuel or fuel pressure is leaking back towards the pump. This might be completely wrong but that's what I have understood from it, maybe someone can enlighten me on the matter? 

[ndxturbo]

Also when I take it to garage tomorrow I will mention the temp sensor to them and see what they say

[ndxturbo]

Took it to the garage today and they had it for a couple of hours and found nothing  leaving it there overnight though to see what it does in the morning for them. Started it this morning in the way I have been the last few days (cycling the key 3 times), and it didn't have the extended crank, but it didn't sound like a solid start to me, almost like I didn't keep the key turned long enough (which I may have done so that might be my fault). Will keep you updated

[ndxturbo]

As predicted, the garage found nothing wrong with it (in terms of fault codes). Complete waste of time taking it there. To me it seems if they find no fault codes then they suspect nothing is wrong when there clearly is :/ Looks like I'm going to have wait it out and see if it gets worse, or try find a decent mechanic who doesn't rely on a computer....

[itavaltalainen]

What's the engine code (wiring diagrams are specific to code)?

You can check the temp sender using a multimeter.... http://www.motor-talk.de/forum/aktion/Attachment.html?attachmentId=719242
It's obviously in a different place on the mk4 but the procedure is the same and the values you should be getting from sender on mk4 are quite similar.

If this is OK and cycling ignition before you start helps the car to start I would be looking at fuel pressure regulator (sounds like it allows petrol to leak back into the tank - normally the fuel pressure should not drop a great deal over night).

[ndxturbo]

What's the engine code (wiring diagrams are specific to code)?

You can check the temp sender using a multimeter.... http://www.motor-talk.de/forum/aktion/Attachment.html?attachmentId=719242
It's obviously in a different place on the mk4 but the procedure is the same and the values you should be getting from sender on mk4 are quite similar.

If this is OK and cycling ignition before you start helps the car to start I would be looking at fuel pressure regulator (sounds like it allows petrol to leak back into the tank - normally the fuel pressure should not drop a great deal over night).

I have no idea what the engine code is  all I know is that it's a 99 GTi mk4 lol

thanks for that I will look into it, would you reckon it's worth changing the temp sensor anyway just eliminate the possibility? and the fact that they're pretty cheap to replace.

Since the last extended crank I have been cycling the ignition 2-3 times + had the fuel filter changed, so far I have not had an extended crank, even been recording how long the car has been sat for each time I start it, longest it's been sat for is 16 hours in the last 6 days and it started fine. I'm going to keep doing this for a few more days and then stop cycling the ignition and see what the results are.

Cheers

[itavaltalainen]

engine code is on service sticker on the cambelt cover, in service manual or the service tag in the boot
(there is no mk4 "gti" as all it was is a trim level, you could have it with a number of different engines).

Why replace the temp sensor, test it first.... only takes 5 minutes

sounds to me more and more like FPR allows petrol to leak back to tank

[ndxturbo]

engine code is on service sticker on the cambelt cover, in service manual or the service tag in the boot
(there is no mk4 "gti" as all it was is a trim level, you could have it with a number of different engines).

Why replace the temp sensor, test it first.... only takes 5 minutes

sounds to me more and more like FPR allows petrol to leak back to tank

oh okay, in that case I'll have to have a look later...I have no multimeter to test it, is that the only way to test it?

[itavaltalainen]

you can also read live temp from ECU if you have access to VCDS (compare the temperature from dash with temperature value in ECU - up to 70 degrees they should agree fairly closely.

multimeter is only 5£ in any diy store thou