5th injector?

I have been to look at a MK1 gti to possibly purchase, but it has a 5th injector, what and why are these installed??

Are they for performance only, or smooth running??

All advice is grately appreciated thank you in advance

The 5th injector is the Cold Start Injector.  It is used for 8 seconds when starting the engine when cold to richen the mixture.  It is controlled by the Thermo Time Switch.

It is located on the cam belt end of the inlet manifold.

Cheers

Rich

Are the 5th injectors standard, or have modifications been carried out Possibly due to cold start problems?

Completely standard

The 5th injector is a standard feature of most earlier fuel injection systems. (Later ones have the electronic capability to increase fuel delivery at startup through the regular injectors). It provides extra fuel, to overcome the cold temperature of the piston/cylinder at startup. I guess less vapourises and neat fuel exits from the exhaust.

Other cars (I don't think K-jetronic, though) also use the 5th injector to provide enrichment in situations such as acceleration demand. So, it could be used to enhance performance, but not in the Golf GTI. The Golf varies the stoichiometric ratio by the shaping of its air mass meter (which is a mechanical device, not electronic) and the 4 regular injectors have enough capability to provide the extra fuel.

stoichiometric ratio

Exactly what I was gonna say.

If my 5th injector were blocked/knackered would that explain why I have to keep the revs up to about 1800 when I start my engine for the first time of the day? If I don't it dies. After about 10-15 seconds of revs it's fine.

probably not.

The manual says you should slightly depress the accelarator when starting a GTI.

I have my 5th injector unplugged (another story) and Mine starts up fine.

Your problem could be so many things. Would need to do some simple tests and identify other symptoms to diagnose. E.g. could be ignition.

Peter.

paul_c said

 stoichiometric ratio

Far too long a word for a monday morning.  :roll:

tallpete said

probably not.

The manual says you should slightly depress the accelarator when starting a GTI.

I have my 5th injector unplugged (another story) and Mine starts up fine.

Your problem could be so many things. Would need to do some simple tests and identify other symptoms to diagnose. E.g. could be ignition.

Peter.

On my car it should say 'fully depress the accelerator' and maybe 'pray'

I can always sort that problem out for you Turbthenicsmk1 by taking it off your hands I`ll look after her…..
                     :wink:  :wink:  :wink:

There goes the deposit on the house Kev  

Infact, the last time I drove my Mk1 was when I saw Alec open his garage door to show me his rather nice Mk1