Fuel Pressure for Starting Engine / Missing Valve?

hi peeps,
my mk1 is a bit of a mongerel.  ABF engine in a (originally) carb clipper.

it is a bit of a pig to start.  when I half-turn the ignition I can hear the pump priming but when I try to start it turns over but does not catch.
it will start, usually after 5-10 tries.

I'm wondering if it's missing a valve somewhere in the fuel line which means that after the pump stops, the pressure drops off at the engine?  sounds likely?

I was told that some polo fuel filters have a valve in them - could I just swap one in and see if that helps?

ta!

what engine management is it, k-jet or abf?

it's got the mk3/Seat ECU, does that help?

ideally to start with get it plugged into vag-com, but that depends if whoever did he conversion wired it in for you!

ok i would start with a new vw ecu temp sensor, and also an ecu relay, though that depends if there is one. do you know who did your conversion loom?
id say a fueling problem is unlikely if it does eventually start and run ok, but a fuel filter change can never hurt as its cheap and easy to do. main thing is to ID what one it is, as that depends how the fuel system was modified for the abf.

ok, next time I get the car out I'll take some detailed pics of the relevant items.

one thought - once it is running the fuel pump is running too so the pressure at the engine would be fine.  it just seemed to be suspicious that once the pump stopped after priming it won't start.

it is easier to start again once it is warmed up, almost always "only" 2 or 3 attempts…

the priming isnt really important anyway, as soon as the pump kicks in when engine is cranking anythign the priming does will have been achieved pretty much instantly anyway.

if you mean it will only prime once when you turn the key and repeating the starting procedure doesn't make the pump prime again, this is normal. the abf ecu will only prime the pump the first time, after that there is quite a long delay before it will prime the pump again. just as long as the pump runs whenever the car is cranking everything is ok

aha, from what you've said it is beginning to make sense:

1) I can hear the pump priming whenever the key is turned.  I can prime multiple times before even trying to turn the engine over.

2) I'm pretty sure that the pump is off when the engine turns over.  problem…?

2. this is a problem, it means the ecu isnt seeing an rpm signal. i would say that your crank sensor is dodgy

okey dokes, I'll give it a look.

had a little read about it on the abf, would it not affect the running if it was dodgy?

To confirm this, you could run a live (with a fuse and a switch) direct to the fuel pump.
Turn on the ignition, and turn on the switch. The pump should now run constantly. When you crank the car, if it jumps into life, there you have it - Pump not getting power when it should under normal conditions. "Why" will be another line of investigation!

crank sensor is a funny thing, they can fail so that car doesn't run, or can be intermittent so it works sometimes then cuts out and wont start, sometimes they only fail when the engine gets hot! basically if its the original sensor just replace it, only £50 from GSF