Hot starting problem (MK1_BOY)

[richandhazel]

Hope someone can give us some inspiration as we're facing defeat with this problem  :-[

Marcus (MK1_BOY) came round yesterday with a problem with his Mk1 GTI Campaign that I just can't fix.  

It starts fine when cold, however when hot and left for between 10 minutes to an hour and a half it just will not start. I've checked for the favourite, dripping injectors. Its definately not that. In fact it seems to be the opposite, no fuel. Pulled an injector out and sure enough, no fuel. Took the boot off the metering unit and lifted the sensor plate and sure enough fuel came out of the injector. The sensor plate is correctly positioned at the bottom of the cone and is central.
Cracked the supply line to the metering unit and we have good fuel pressure, so I'm guessing its something to do with the metering unit.
Anyone got any ideas? Just seems really odd that it only does it when the engine is hot.  
 

[Justins145bhpMK1]

Or if its not the metering unit could it be wrongly routed fuel lines, ahd a similar problem before when a fuel line ran near the manifold causing fuel evaporation??

[mk1]

Check that the fuel system is holding pressure when the engine is off. Had a fault like this, changed the pump and accumulator and this fixed the problem. Think it was the non return valve in the pump letting the fuel back, or the acc. was dead so could not top up residual fuel pressure when the engine was not running. Low fuel pressure causes the fuel to boil in the lines and you end up with a vapour lock, let the engine cool and the fuel vapour condenses and the engine starts. There was a mod for earley Porsche 924 that used a relay to fire the cold start injector while cranking to help this. (different circuit to normal cold start) Hope this helps, Steve.

[MK1_BOY]

Cheers for all your help fellas, just to add insult to injury It misfires when I've been driving for a while, thought Rich and myself had sorted that one but it seems not....  its got to the stage the other day when it stared to misfire and within 10 minutes it actually cut out on me on a hill, turned the engin off, turned it back on and it was fine...  Its as if my top water hose has burst and it spraying all over my dizzy cap( I know this cos it hapened to me the other month) but we've checked the Dizzy cap and it seems fine...   Think you boys may have the right Idea, I'll have a check asap....  Again cheers for all your imput fellas...  

[richandhazel]

We do have a Mk2 one that we can try. I think the metering unit itself is the same, its just the airbox thats different.

The only thing i can suggest is going to a scrappy and getting hold of another metering unit. Gotta be worth a try.

[richandhazel]

Thats a good one to look at, I'm sure they are routed correctly but its well worth double checking, thanks

Or if its not the metering unit could it be wrongly routed fuel lines, ahd a similar problem before when a fuel line ran near the manifold causing fuel evaporation??

[richandhazel]

This could be it Marcus, its certainly been mentioned more than once before and well worth looking into, thanks Mk1.

Marcus, I also took the liberty of of posting the question at ClubGTI. This NRV has also been suggested there too:-

http://www.clubgti.com/forum/topic.asp?TOPIC_ID=26848

I think we ought to look at that, especially as you replaced your fuel pump recently.

Check that the fuel system is holding pressure when the engine is off. Had a fault like this, changed the pump and accumulator and this fixed the problem. Think it was the non return valve in the pump letting the fuel back, or the acc. was dead so could not top up residual fuel pressure when the engine was not running. Low fuel pressure causes the fuel to boil in the lines and you end up with a vapour lock, let the engine cool and the fuel vapour condenses and the engine starts. There was a mod for earley Porsche 924 that used a relay to fire the cold start injector while cranking to help this. (different circuit to normal cold start) Hope this helps, Steve.

[VWnut]

I had the same problem on my MK1. It turned out to be the fuel return valve. The fuel wasn't returning to the tank when i parked up thus causing vapour locks in the fuel lines due to the heat of the engine. When i restarted the car it either cut out straight away or misfired for a while afterwards.
Hope this helps.
Tom

[MK1_BOY]

Worth a shot...  Just need to find out what that is  Gonna have a try of all these on Sunday..  1 other thing, I took her out Wed night for 15 minutes and after 10 she started misfiring.. Now I've had this problem reciently in the past where it was misfiring and it turned out to be the ignition coil, after a very expensive route(I know my fuel pump will be fine for a few years) and it turned out to be the connection from the wires to the ignition coil BUT could this cause all my other probelms.  Most syptoms make sence but the lack of fuel Any other last thoughts B4 I have to look at the metering unit?? Please??

[richandhazel]

Hi Marcus, just found this:-

Starts hard hot- A couple things to look at are system pressure at rest, and CO setting. If the check valve won't hold rest pressure you will have a heck of a time getting going again after the car sits for 5 minutes. The spec for holding system pressure is that it must hold at least 20 psi for 1/2 hour

at: http://ncr-pca.org/tech/tech-cis.htm

Maybe something went wrong with your NRV when you changed your fuel pump???