problems starting when warm

hi all
ive started having problems with my 83 gti 1.8 inj
i have trouble starting it when its warm….but it starts fine when cold ?

someone told me that it could be the crank angle sensor  ??

could anyone please verify this, or give me any other reason why
also where to find the sensor (pics if poss)
sorry not very mechanically minded…still learning
cheers
dave

The Mk1 Golf doesn't have a crank angle sensor.

It could be many things. Is it flooded? Can you start it if you put your foot on full throttle and crank it over (release once its starting)? If so, then leaky injectors. The other thing it might be is poorly adjusted mixture or faulty WUR. For these kinds of issues, you'd need proper instruments to diagnose.

paul_c said

The Mk1 Golf doesn't have a crank angle sensor.

It could be many things. Is it flooded? Can you start it if you put your foot on full throttle and crank it over (release once its starting)? If so, then leaky injectors. The other thing it might be is poorly adjusted mixture or faulty WUR. For these kinds of issues, you'd need proper instruments to diagnose.

no its not flooded or anything like that
it just wopnt fire up when warm

its something to do with the air flap inside the airbox/injector housing
if you undo the catches, put your finger under and lift the big flap  IT STARTS  and then runs fine thereafter ?

Could be too lean mixture, which would point to a faulty/sticking metering head, poorly adjusted mixture or faulty WUR, or possibly an air leak. Plenty to check!

paul_c said

Could be too lean mixture, which would point to a faulty/sticking metering head, poorly adjusted mixture or faulty WUR, or possibly an air leak. Plenty to check!

not sure its anything to do with leaks or lean  mixture as it starts fine when cold and also runs fine when started
its just that start up when warm.

could poss be the WUR
NOT SURE WHAT YOU MEEN BY STICKING METERING HEAD

like i said im not very mechanically minded…still learning (newbie)

They stick, the flap stays down when it should go up (due to the pull on it by the vacuum from the engine) so there's no fuel, so they don't start, etc.

Its possible the plate requires adjustment (it should be in the centre of the cone), the other thing it can be is the hinge is gummed up with something sticky, or the pin which controls the fuel amount, is gummed up too.

paul_c said

They stick, the flap stays down when it should go up (due to the pull on it by the vacuum from the engine) so there's no fuel, so they don't start, etc.

Its possible the plate requires adjustment (it should be in the centre of the cone), the other thing it can be is the hinge is gummed up with something sticky, or the pin which controls the fuel amount, is gummed up too.

no the plate is free and very loose
ive also swapped it with a spare head that i had, and it still does the same

what actually makes the plate lift up/or why would it not if it was free and not sticking ?
what controlls it ?

Its lifted by the vacuum created by the engine. Ie during the intake stroke, the piston goes down and the inlet valve is open. Even if the throttle is closed, there is a little air which gets past its butterfly and/or the idle bypass circuit, its this vacuum which pulls the flap.

Hence, if you have a vacuum leak, the engine sucks but through the leak, not the metering head - and the engine runs lean. Maybe not starting.

When its cold, it might start even with a vacuum leak 1) because the cold start/5th injector squirts some fuel in too; 2) because the WUR adjusts the control fuel pressure so there's more fuel anyway, and 3) because the K-Jet system tends to run rich during startup/warmup.

paul_c said

Its lifted by the vacuum created by the engine. Ie during the intake stroke, the piston goes down and the inlet valve is open. Even if the throttle is closed, there is a little air which gets past its butterfly and/or the idle bypass circuit, its this vacuum which pulls the flap.

Hence, if you have a vacuum leak, the engine sucks but through the leak, not the metering head - and the engine runs lean. Maybe not starting.

When its cold, it might start even with a vacuum leak 1) because the cold start/5th injector squirts some fuel in too; 2) because the WUR adjusts the control fuel pressure so there's more fuel anyway, and 3) because the K-Jet system tends to run rich during startup/warmup.

so you think i might have a vacume leak somewhere ??
where could that be  ??
is there any way of checking /

I don't know, I'm not in front of the car, all I can do is make suggestions and you look at it (or a friend, or a garage, etc).

Vacuum leaks are kinda tricky to find. One way is to physically inspect all the bits and bobs for loose connections, cracks in rubber, holes etc. Another is to spray some start fluid at the components and see if the engine note changes. The way garages do it is using a smoke machine.

paul_c said

I don't know, I'm not in front of the car, all I can do is make suggestions and you look at it (or a friend, or a garage, etc).

Vacuum leaks are kinda tricky to find. One way is to physically inspect all the bits and bobs for loose connections, cracks in rubber, holes etc. Another is to spray some start fluid at the components and see if the engine note changes. The way garages do it is using a smoke machine.

ok
will av a look,, see wat i can find

cheers
dave