problem with fuel injection

Hi

I am having trouble with the fuel injection system on my 89 cabby 1.8gti. I have tried the injector test which is posted on this site, and I am having no luck. I Had all of the injectors resting in the each individual bottles, and when I turn the fuel pump on ( I can here it running) the valves are not opening at all, even when the air flap is raised. When I removed all of the injectors, and just placed the leads in the bottles and repeated the test, there was an equal amount of fuel coming out and was slowing or speeding up when the air flap was raised or dropped, so I know there is fuel getting to where it needs to go and the metering head is behaving they way it should. I have also tried disconnecting all fuel lines/ filters etc, and blowing an air line through to clear any blockages, this did not make any difference. I have also tried attaching all of the injectors to an air line to see what pressure they open at, all open at 4.5 bar which is correct isn?t it?

From this I can only think it is something to do with the fuel pressure out of the pump, I wouldn?t think it?s a faulty pump as I have not long had it. Is there any way of altering the fuel pressure to allow the injectors to open?

Many thanks
Andy

I thought the injectors need to open at more liek 3 bar than 4.5 bar. So it sounds like your injectors are faulty, but then I'm not sure you can test using a compressor to get the point they open??? Fuel and air are completely different, ones a liquid and one's a gas and these behave differently.

You could do a system and control pressure check, its possible your fuel pump is weak or your system pressure is too low, which would also mean the injectors don't open.

Right, I have now gone back and tested the fuel pump, by taking it off the car and connecting it to a 50 metre coil of pipe, and attaching a pressure gage to the end. By the time the liquid reached the end of the 50 metre coil, the pressure gage was reading 150psi, which exceeds the required amount to open the injectors. After this, I connected one of the injectors to a piece of pipe leading down to the pump, and tried pumping water through to see if this would open the injector, it worked perfectly. This has led me to believe there is a significant drop in pressure in the metering head. Is there a way of increasing the pressure on the metering head to the injectors?

thanks

mk1andy said

Right, I have now gone back and tested the fuel pump, by taking it off the car and connecting it to a 50 metre coil of pipe, and attaching a pressure gage to the end. By the time the liquid reached the end of the 50 metre coil, the pressure gage was reading 150psi, which exceeds the required amount to open the injectors. After this, I connected one of the injectors to a piece of pipe leading down to the pump, and tried pumping water through to see if this would open the injector, it worked perfectly. This has led me to believe there is a significant drop in pressure in the metering head. Is there a way of increasing the pressure on the metering head to the injectors?

thanks

There IS a significant drop in the metering head - by design!

Basically, you need to measure the system pressure and the control pressures, to know if its in spec or not. System pressure can be varied by adding/removing shims to a valve. All in the Haynes…

Hi mate just a quick test try adjusting the fuel air mixture screw on the metering head worth a try if you havent already!!!!!!!!! :scratch:

Hi - like paul_c says the only way to diagnose the gti system is with a fuel pressure test.  I sell test kits at www.golfmk1.co.uk.

I'd suspect the pump - I had a car in a few months back that would run (just) but when doing the injector test had the same fault as yours.  System pressure was just down on spec.

Fitted a new pump and all was dandy.  Subsequent checks showed the WUR was fauly too - cleaned out with an air hose and all was good.

The point being the system pressure tests showed all of the faults.

Cheers

Rich