hard to start-fuel or electric fault?

Hi,
     my 1983 gti has developed the following problem and I hope someone can help…
  
Car has been going fine always starting ok. Then recently I filled car with fuel.
 It developed an intermittent misfire for next 15 miles home. Next morning after cranking over for 5mins it wouldn't start.
On investigating I found that there is no spark at plugs, so cleaned dissy, rotor arm etc. No use. Fuel pump runs, and there is a feed to the coil.
Then after a while car fires up, no misfire no problems. Take for 10 mile test run. Stop/start a few times no problem.
Put car in garage for 4 hours or so and try to start. Same problem-no spark. Swap coil+rotor arm with known good one from my other gti as well as ignition module, still no spark at plug. After umteen attempts, car will fire and run no problem.
Now, I am wondering if there is something more fuel related. I am thinking there could be some interlock between not getting fuel through, therefore there is no spark to ignite? I did have a rotten fuel filler neck which I replaced a few weeks ago after getting car. I am also thinking dissy, but why does everything run great once it eventually fires?  Any help/advice greatly appreciated.  Mike.

Mike,

There is no fuel related control of the spark.  There is control of the fuel pump relay by the coil so that if the coil is shut off and the ignition stays on the fuel pump shuts off.

Are you really sure that there is no spark? How are you checking it? Does sound like a fuel problem especially when you've tried all those ignition parts.

Cheers

Rich

Hi Rich,
            thanks for the reply. I am checking for a spark by grounding a plug and connecting no1 spark plug to it. As it is quite dark it is easy to see if there is a spark and there is none. Then try with the other plugs in turn. All plugs are new, and also using new spare.Today I swapped the dissy top and leads with another gti and nothing. also checked the signal from the dissy hall sender to the electronic box as per the Haynes manual. I was getting 4.5 volts turning the engine over by hand at the crank. After doing this I tried to fire her again and she started ok. Still getting 4.5v while running.( the other gti pulls 6v when doing these tests, but seem within spec.)I took her for a 15mile run and she finally cut out, although I was going quite quick at the time. I was wanting to see if there is a fault with the rev limiter or something! Started after 1/2 mins and ran ok home. Also started umpteen times after this.
  I will start her up later to see if she goes after not being run for 5 hours and see.  Any more ideas appreciated.
                                                         che
ers,Mike.

Wierd.

So you've replaced almost all the electrical system?

Do you have an immobiliser fitted?

Hi Rich,
             problem solved! Last night went into garage and car started first time after sitting for 5 hours. This morning car would not start so took motorbike to work.
 Anyway… I had decided to change over the distributer and lined camshaft up etc. when I decided to double check Hall sender. this time I got a constant feed of 6.5 volts when turning engine over by hand. I knew yesterday that it was alternating between approx 1v and 6v as per Haynes specification so knew something was not right. I pulled off the rubber boot over the connection and found that one wire was broken off and another was almost off. I can only assume that with me pulling connections on/off that sometimes it was made and othertimes it wasn't. Still strange how leaving car to cool broke the connection.
 I joined wires up and tested. Fired right away. Hope to repair wires tomorrow.
                             cheers,Mike.

Good news mike  

Cheers Rich,
                   Good to find it in the end as it was a pain. Intermittent faults can be a nightmare. Could have been worse as I might have been a few hundred miles from home!
By the way, I was going to use the wiring from my Campaign that I need to renovate, but the distributer is different, though both cars are 1993 models. Have to take loom to my work where I will solder it and heat-shrink the connections.
                                       thanks for the help, Mike.

Pre and post Campaign looms are different I think due to the MFA etc