Mk1 Caddy Sport (8v GTI) no injector spray when cranking, but there is when priming.

Hello all!

I`m new here, and in a bit of a pickle.   I hope someone can help me out!

My Mk1 Caddy Sport is a bit stuck. It`s GTI engined, 8v K jet.

It wont fire up except for when its been sat for a while, then it will run for a very short time, (quite well) before dying, after that then completely refuses to start at all.

I popped off a couple of the injectors to test the spray.   they both behaved the same way -  when I turn the key and the fuel pump primes I get a single conical spray. but when I crank for longer they don`t spray at all.

 I would have thought they should spray constantly whilst cranking?

Any help here greatly appreciated as it is blocking my neighbours drive many many thanks!

Mark

 

K-Jet is a pressure differential system, you really need to measure both your system and control pressures.
The system pressure will tell you if your pump is working and it should be around 5bar.
The control pressure is managed by the WUR, think of it as k-jets "choke", at cold the pressure should be 1bar and hot about 3.4bar. This pressure controls how far the fuel metering pin moves for a given amount of air being drawn by the engine, hence low pressure at cold for more fuel and high pressure at hot for less fuel.
Knowing the pressures is vital to fault find the system.
A few things to check:
Does the metering pin move smoothly in the metering head?
Do the injectors leak after shut off?
How long does the system pressure hold after shut off?
Are the input and output gauzes of the WUR clean?
Has the fuel filler pipe ever rusted, been replaced?
When was the last time the fuel filter was changed?
Do you have any air leaks?

Hey Ade!   Thanks very much for this informative reply!   will start taking a look at those things. Possibly a silly question.  what is the WUR?

In the meantime today I was playing about with the relays. I swapped a different one in from the board into the fuel pump relay socket.. this relay stays on with the key, and keeps the pump running after prime (just keeps on going. and doesn`t stop) . but under this relay the car idles fine.

I guess something may be wrong with the relay?   or something related to it?

I forgot to say.  this whole thing started after it was revved from a head gasket swap, so everything had just been put together , it idled well and I ran it for a bit.  tried blipping the throttle a few times and then it died and wouldn`t start properly after that.

in case those are any additional clues to the issue.


Many thanks!

The WUR is the Warm Io Regulator mounted on the front of the block with two fuel lines.
Sounds just like your fuel pump relay has failed then. Some prime the pump, some do not, it doesn't really matter. They have a safety feature, they have to see the ignition tacho pulses to keep the pump running.
They do fail by overheating due to the pump wearing out and drawing too much current. Poor crusty pump wiring connections can cause this as well.

Well, I found out what it was. It was something very silly!
 The boot for the air flow sensor was loose and taking in un-metered air.  Tightened up the boot and it fired up and ran reasonably well, with some surging!

I tried tuning it based on this guide :-

https://img1.wsimg.com/blobby/go/b55bc70e-923b-4ddc-9f6f-90e4df0ddf7f/downloads/K-Jetronic%20-%20Measuring%20Duty%20Cycle%2C%20Adjusting%20A.pdf?ver=1616194998871


but my duty cycle readout is always 50.9..  doesn`t matter how much I change the mixture screw.
I tuned it by ear/engine shaking in the end and it seems ok, not perfect, but pretty ok.   not sure why the duty readout doesn`t seem to change though…

Not sure what you are doing with a duty cycle or what it's all about as UK cars did not have a lambda prob/oxygen sensor in the exhaust unless it's the very last year of production (1992) as they had to have cats fitting for emissions.
The website in your link is for a US website and they did have tighter controls on emissions so had a different set to uk cars.

To set my mixture I have to stick in an CO sensor in the exhaust pipe had adjust the mixture to 1.5% to 2% CO but this is best done at a garage that does MOTs as they have the proper equipment

Ahhh, ok!  that would explain it then! I do have the same port with the blue and white, and brown wire near the cold start injector,  the engine is a replacement one, not absolutely sure what  year the engine is, but there is definitely no O2 sensors in the exhaust system.  Didn`t realise all that stuff was for a sensor equipped car.. I thought it was something else in the K-jet system which I`m totally unfamiliar with.   

Thanks very much for clearing that up!  solves my conundrum! 

Mark