MK4 Golf GTI 18t Wont start when warm

[rob1964green]

Hello chaps - Ex-RAF vehicle technician needs help
The Car - Mk4 Golf GTI 1.8T (W) 2000 AGU Engine

The Fault.
Vehicle cold (first start of the day) insert key, ignition on (all ignition lights go out and hear the pump priming - no throttle applied) turn to start position and vehicle fires and drives fine.
Drove to Northallerton (engine at normal temperature) switch off. Return to vehicle 30 minutes later, insert key, fuel pump primes and ignition lights go out (no engine warning) turn key to start position, engine turns over and strong smell of fuel (no throttle applied) but not an inkling of a spark! If I repeat the start procedure, the smell of fuel just gets worse (as if the old fashioned flooded). Leave the vehicle to stand for approx 15 minutes and try again, engine 'coughs' and I manage to catch it with a bit of gas and it runs fine, initially with a strong smell of fuel again? But... if I don't catch it, the more I try to start it, the worse it gets and refuses to run at all.

I have fitted a brand new set of plugs (NGK-R as were already fitted) and when it's running it drives fine, doesn't cut out or 'hunt' although I notice the rev counter rising and falling from 800 to 1100rpm on occasion at tick over. 

It's a curious one! smells like flooding/over fueling? So why after it has been stood does it start with a bit of gas? Dont have Vag Com or code reader, this is the beginning of  the hunt.

One thing I was gonna try is to get it warm, switch off and remove 1 coil pack, put a plug in it and try to start it... that way I can see if it's sparking when it wont start???

Any suggestions chaps? Tallyho

[barrym381]

temp sensor can cause this and its not expensive or hard to fit 

[dom]

As Barry says coolant temp sensor can cause the symptoms you have described, that's where I would start.

[rob1964green]

Thanks for the prompt replies lads.

My thinking about your suggestion is...

Are you saying the temp sensor tells the ECU engine is cold? Thus supplying more fuel than needed?
I don't suppose there is any way of checking it? (with a resistance/voltmeter).

Only had the car 2 months, so still finding my way around. Would like to know if there are any instruction vids for the injection system and all the damn sensors (The fluffle vlave on the wotsit, tells the cambender to retrard the jizz mixture etc)

Any thoughts on my idea of removing a coil pack and sticking a plug in it to see if it's sparking when it wont start?

Here's hoping - chocs away!
I say Caruthers "Damn short runway - What? Yes sir, but a 1000 yards wide???

[barrym381]

Thanks for the prompt replies lads.

My thinking about your suggestion is...

Are you saying the temp sensor tells the ECU engine is cold? Thus supplying more fuel than needed?

yes your right best just changing it for a new 1 from the dealer 

[xxChrisxx]

A temp sensor wouldnt stop it starting completely. You are more likely to have trouble firing. A car will start even with a huge amount of excess fuel.

Also if its the temp sensor you'll have seen funny temp readings.

I'll put my money on this being down to the crank sensor.

[jamie16v]

A temp sensor wouldnt stop it starting completely. You are more likely to have trouble firing. A car will start even with a huge amount of excess fuel.

Also if its the temp sensor you'll have seen funny temp readings.

I'll put my money on this being down to the crank sensor.

the car is showing that it is over-fueling, if it was the crank sensor, the ecu would have no signal to tell the injectors when to activate.  I would say a dodgy crank sensor would stop it starting completely due to the ecu having no reference signal.
I think its the CTS too, think of the action of leaving the choke on! I have actually come across this problem before, and also a dodgy crank sensor and the symptoms are not alike.
another thing I could put it down to is an overheating ignition module but I doubt its that because its recovering when cold.

[xxChrisxx]

The bets on.

[houston]

The temp sensor supplies 2 readings, one to ecu and one to display. It's an easy cheap fix and common fault so best to replace it and see if it works before you go looking for other causes

If it was crank sensor then engine temp wouldn't come into it, it just wouldn't start

I'm assuming you've scanned for codes? Would be no eml as its an agu

[rob1964green]

Thanks again lads for the info.

As I mentioned only had car 2 months and problem free until now. Clearly I need to have the codes read before continuing any further, although... I approach this with a good deal of trepidation! So many posts say the code reader says this, the code says that etc and it turns out to be something completely different and usually expensive... Still, it's a place to start?

Forgive my ignorance.. but what is EML and why does the AGU engine not have it?

FYI. The temp gauge has no fluctuations and works fine (nothing different from when I got it).

From my techy days... If it was a failing ignition module (do you mean coil pack?) given there is 1 per cylinder... I would be able to hear the difference (running on 3 cyls not 4) and there would be a significant power loss. It still leaves my cheeks on the parcel shelf when I boot it!

So.. plan of action... 1. Get codes read.  2. Mortgage House.  3. Buy butt plug.

Will keep you informed lads... cheers. Rob