MK1 Golf GTI - Warm start problems

Hi

Ive been struggeling with this problem for quite some time now. Ive fully restored my Golf 1 GTI and this is the last bit to make it 100%.

Engine is a DX with 112 ps completely standard all the way through.

When its cold it starts perfect from the get go on all 4 cylinders.

When the engine is warm and i shut it off - 10 minuters later it wont start proberly. Everytime i have to turn the key over and hold the starter for 15-20 seconds until it humps into life but only on 3 cylinders for the first 3-5 seconds.

Ive really tried everything..

Injectors are not leaking when warm or cold.
Injectors adjusted to give equal amount of fuel on each injector. (Which means they all are spraying nicely)
CSV are not leaking when warm or cold.
CSV unplugged does not make a difference.
Water temp sensor changed to a brand new one, did not make a difference
Fuel pump delivers more then enough fuel.
Fuel pump return valve changed to a brand new one, did not make a difference
Brand new fuel accumulator
System control pressure is OK

Anyone know what els to check ? Ive given up cf_emoticons__BangHead:cf_emoticons__BangHead:cf_emoti
cons__BangHead:cf_emoticons__BangHead:cf_emoticons__BangHea
d:cf_emoticons__BangHead:Ive created a movie clip to show the problem.

http://www.bilgalleri.dk/video/diverse_bil/52773-g1

Hope someone can help me out.

Hi
being there done that, eventually found using super unleaded fuel cured any future hot starts problems on my gti, she always starts on the button when superunleaded even on the hottest of days.

bazmk1 said

Hi
being there done that, eventually found using super unleaded fuel cured any future hot starts problems on my gti, she always starts on the button when superunleaded shes is cooking under the bonnet.

Even although its new, it sounds like a faulty accumulator

I've never experienced the problem with my own car but this seems to be a common issue and one without a definitive answer.

This is only my theory and you say you have checked your control pressure and I am open to correction but I used to work on old Rolls Royce engines and they suffered in a similar way……..

I wonder if its to do with the system pressure regulator valve inside the metering head?

If this valve is weeping the system will lose pressure - not a problem while the engine is running as there is more than enough spare capacity from the pump to overcome any loss.

However petrol like most liquids boiling point decreases with lower pressure.
When the engine is switched off and system pressure drops away quickly due to this valve weeping then the heat inside the engine bay could make the petrol begin to boil inside the system if it were at a lower  pressure than it should be.
Especially in the pipes going to the injectors that are in braided steal and right above the hot exhaust manifold.
In a system that holds pressure then its not a problem as the pressure holds up for a lot longer and by the time the pressure has dropped then so has the under bonnet temperatures.
When petrol boils it creates vapour locks within the pipes and rather than atomised fuel being squirted by the injectors on a hot start you could be getting atomised vapour instead creating a too weak mixture.
When the engine bay temperature falls away again then the vapour returns back to liquid and your cold start is fine.

As I say its only my theory but one way to check would be to check your system pressure 10 minutes after stopping. You do say your control pressure is OK so I assume that you have checked both system and control pressure at the same time?

Edit….
I just did some digging on google and found these 2 articles….

http://www.flightglobal.com/pdfarchive/view/1942/1942%20-%202672.html

Also another post mentions that using higher octane fuel stops his problem and this article mentions that higher octane fuel boils at a higher temperature although there is a bit of disagreement with the poster's facts.

http://www.thenakedscientists.com/forum/index.php?topic=45370.0

HI

Thanks for your answers.

Im already running on 99 octane.

Im currently testing the hold pressure and system control pressure.

Seems my fuel pressure is dropping almost instantly

Eventhough my returnvalve are new.

Yomp said

I've never experienced the problem with my own car but this seems to be a common issue and one without a definitive answer.

This is only my theory and you say you have checked your control pressure and I am open to correction but I used to work on old Rolls Royce engines and they suffered in a similar way……..

I wonder if its to do with the system pressure regulator valve inside the metering head?

If this valve is weeping the system will lose pressure - not a problem while the engine is running as there is more than enough spare capacity from the pump to overcome any loss.

However petrol like most liquids boiling point decreases with lower pressure.
When the engine is switched off and system pressure drops away quickly due to this valve weeping then the heat inside the engine bay could make the petrol begin to boil inside the system if it were at a lower  pressure than it should be.
Especially in the pipes going to the injectors that are in braided steal and right above the hot exhaust manifold.
In a system that holds pressure then its not a problem as the pressure holds up for a lot longer and by the time the pressure has dropped then so has the under bonnet temperatures.
When petrol boils it creates vapour locks within the pipes and rather than atomised fuel being squirted by the injectors on a hot start you could be getting atomised vapour instead creating a too weak mixture.
When the engine bay temperature falls away again then the vapour returns back to liquid and your cold start is fine.

As I say its only my theory but one way to check would be to check your system pressure 10 minutes after stopping. You do say your control pressure is OK so I assume that you have checked both system and control pressure at the same time?

Edit….
I just did some digging on google and found these 2 articles….

http://www.flightglobal.com/pdfarchive/view/1942/1942%20-%202672.html

Also another post mentions that using higher octane fuel stops his problem and this article mentions that higher octane fuel boils at a higher temperature although there is a bit of disagreement with the poster's facts.

http://www.thenakedscientists.com/forum/index.php?topic=45370.0

HI
Coudnt agree more, thats exactly why i use esso or bp superunleaded only, i swear my mk1 gti will not start hot on 95 fuel with the exact systems as first mentioned.  

W65_Pirelli said

HI

Thanks for your answers.

Im already running on 99 octane.

Im currently testing the hold pressure and system control pressure.

Seems my fuel pressure is dropping almost instantly

Eventhough my returnvalve are new.

Yomp are think you are completely right ! Also makes sense when i start, i only start on 3 cylinders.

Just finished my testing before i had to go eat, and my pressure for sure is dropping too fast

So its either my return valve in my fuel pump or it could be the valve inside the fuel distributor (kjet)

bazmk1 said

HI
Coudnt agree more, thats exactly why i use esso or bp superunleaded only, i swear my mk1 gti will not start hot on 95 fuel with the exact systems as first mentioned.  

Running on super to overcome this means you are only treating the symptom and not the cure.

Mine starts fine both hot and cold on both fuels so there must be a fault somewhere.

W65_Pirelli said

So its either my return valve in my fuel pump or it could be the valve inside the fuel distributor (kjet)

If you've changed the non return in the pump then it can only be the regulator in the metering head.
Leaky injectors would only lose the pressure between the head and the injectors.

If its inside the metering head it can only be bad o-rings.

I have a spare return valve ill give a go tommrowo

Yomp said

W65_Pirelli said

So its either my return valve in my fuel pump or it could be the valve inside the fuel distributor (kjet)

If you've changed the non return in the pump then it can only be the regulator in the metering head.
Leaky injectors would only lose the pressure between the head and the injectors.

Hi
Your wrong, this exactly where the vapour lock occurs with the heat of the exhaust manifold causing the petrol to vapourise in these lines which inturn the car will not start as the vapourised petrol will not operate a mechanical injector unless turned over for ages.

Yomp said

bazmk1 said

HI
Coudnt agree more, thats exactly why i use esso or bp superunleaded only, i swear my mk1 gti will not start hot on 95 fuel with the exact systems as first mentioned.  

Running on super to overcome this means you are only treating the symptom and not the cure.

Mine starts fine both hot and cold on both fuels so there must be a fault somewhere.

My car starts on the button hot or cold as a gti should so there is nothing wrong i use my motor most days & it runs perfectly
baz

bazmk1 said

My car starts on the button hot or cold as a gti should so there is nothing wrong i use my motor most days & it runs perfectly
baz

I'm not dissing your car Baz! but you did say in an earlier post "i swear my mk1 gti will not start hot on 95 fuel"

I'm confused now!

I admit I may have conflicted myself earlier regards the pipes between the metering head and the injectors as when the engine is stopped I would have assumed that the metering head would lock the pressure in these pipes as the valves in the metering head would be closed therefore isolating the pressure in these pipes from system pressure but I could well be wrong.

However we are in agreement that it's vapour locks in the system due to low pressure and high temperature right?

Yomp said

bazmk1 said

My car starts on the button hot or cold as a gti should so there is nothing wrong i use my motor most days & it runs perfectly
baz

I'm not dissing your car Baz! but you did say in an earlier post "i swear my mk1 gti will not start hot on 95 fuel"

I'm confused now!

I admit I may have conflicted myself earlier regards the pipes between the metering head and the injectors as when the engine is stopped I would have assumed that the metering head would lock the pressure in these pipes as the valves in the metering head would be closed therefore isolating the pressure in these pipes from system pressure but I could well be wrong.

However we are in agreement that it's vapour locks in the system due to low pressure and high temperature right?

Hi
When i put 95 in my motor i get the exact same systems as the vid above when the bay is hot, you have to floor the pedal & keep her turning for about approx half a min, when running 97 esso/bp fuel she bursts into life as soon as you click the key.

I have also got pressure testing equipment which i used to test my system when running 95 that showed me my fuel system could hold pressure on the fuel pump side for well over the recommended 10mins.  But with the fuel pressure gauge still connected & holding pressure she motor wouldn't start unless you turn it over constantly, then with superunleaded she starts in the button so the fuel must be sitting in the injector lines ready to open the sec the pressure goes above aprox 3bar then of course immediately closed again hundreds of times a sec atomising the fuel into a vapour.

mistake

mistake

Hi

If the fuel system is holding pressure on the fuel pump side & you say your injectors are not leaking there has got to be pressure in these braded lines which in turn will raise the vapour point of the fuel. You mentioned you use 99octane fuel is this the supermarket fuel that tesco sell? if so i would take burn of all the 99 fuel & fill her up with esso/bp superunleaded & take it from there
baz

my motor has no problem starting from hot regardless of what fuel is in it. So what's the difference between mine and yours?

They shouldn't need super to start from hot. How do people in Ireland cope? You can't buy super in Ireland.