© www.1600i.de
created by Phil Ade 31.12.2007

1600i Fuel System Diagnosis


Precheck List:-


The following tools are required to test the fuel pumpís delivery:-



Preferred Tool

Suitable Alternative Tool

Glass measuring jug in ml


Remote control VAG 1348/3A with the VAG 1348/3-2 adapter cable.

ECU connector box.

Fuel injection pressure test kit, eg:-

-         VAG 1318 and VAG 1318/10, VAG1318/11, VAG 1318/1 hoses

-         Sealey VSE 210

-         Sealey VSE 211 (with a modified car pump tyre connector drilled out to 9.5mm or 3/8Ē).

Modified car tyre pump where the following bits are used:-


-         Tyre connector (drilled out to 9.5mm or 3/8Ē)

-         Pressure gauge

-         Clothes peg or hose clamp

-         Fuel hose (after the pressure gauge).



Manfred had suggested to me about using a modified tyre valve connector to fuel injection (VW Digijet) test port and it works a treat.


Caution:When drilling out the tyre valve connector, make sure that the following are observed:-


-         Tyre valve connector level unlatched

-         Donít drill into the tyre valve connector too far down !!!


Hereís what Manfredís modified tyre pump valve connector looks like.†† The drilled out one is on the left hand side of the photo below:-




Testing the fuel pump delivery:-


First of all connect a suitable fuel pressure test kit to the fuel injection test port of the 1600i engine bay.This is shown in the following photo below:-







Hereís what the entire setup looks like on my car:-




Note:When testing the fuel pump delivery, make sure that the safety valve on the pressure gauge is open !!!
The previous photo is of my Sealey VSE211 fuel injection test set with the modified tyre valve hose installed.However if you donít have a fuel injection pressure test set, there is a much cheaper method of making your own test set (Manfred came up with the idea).Hereís what Manfredís home made fuel injection pressure test set looks like:-





The clothes peg is used as a safety valve for measuring fuel pressure and is released to measure the fuel pumpís delivery rate.The pressure gauge its self (and the hoses) all came from a car tyre pump and the whole lot only cost him 5.60 Euros (instead of £70 + £3.99 for my Sealey VSE211 + car pump).


This is what Manfredís fuel pressure test set looks like when itís installed on one of his (original) 1600i beetle (the green syringe was used to test the fuel pressure regulator).




There are two methods of testing the fuel pumpís delivery which will be covered below:-



Using the VAG 1348/3A Remote Control (or equivalent):-


To test the fuel pump, remove relay 80 (fuel pump relay) from itís socket.See my photo on the 1600i website for further details (under Electronics, 1600i Engine Bay).


Itís also possible to make up a simple lead with a push button switch box to do exactly the same job.All you will need is the following:-


-         Male spade connector (for the fuel pump relay socket)

-         Female spade connector (to connect to the positive live part of the fuse box)

-         Push to make push button switch.

-         A high current 12V relay.This must have a rating of at least 10 Amps !!These are available from Maplin for about £5.

-         Approximately 5 metres of cable (any old mains flex will do).

-         A small piece of stripboard (if the relay is a PCB one).

-         A small ABS plastic box


Hereís what the circuit would look like:-



Battery plus











††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† ††††† Push to make

Relay 80, pin 4

††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† ††††† Pushbutton switch





Now connect the VAG 1348/3A (or equivalent) remote control and the VAG 1348/3-2 adapter cable from battery positive to pin 4 of the fuel pump relayís socket.Do not switch on the ignition !!!


Operate remote control for exactly 10 seconds.

Using an ECU connector box (Manfredís method):-


This method is different to the one above.To test the fuel pump in this case, do the following:-


-         Disconnect the battery earth

-         Remove the 25 pin plug from the ECU

-         Connect the ECU test boxís lead to the ECU lead

-         Reconnect the battery earth

-         Switch on ignition

-         Short out pins 6 and 13 on the ECU test box to make the fuel pump run for exactly 10 seconds.


Hereís what Manfredís ECU test box looks like:-





The amount of fuel delivered in both cases must be 350ml.If thatís not the case then the following will need to be checked.


-         Fuel pump relay (relay 80) Ė Operation and condition of solder joints.Replace it if necessary.

-         Fuel filter.Replace if necessary.

-         Fuel hoses Ė check for leaks and damage.Also check the fuel lines for blockages.

-         Fuel pump.Replace if necessary.


Fuel Pressure Test:-


To check the fuel pressure of the fuel injection system, do the following:-


-         If a remote control box was connected, disconnect it and re-install the fuel pump relay back into itís socket.

-         If an ECU test box was used, disconnect it and reconnect the ECUís plug back into the ECU its self.


Now close the fuel pressure release valve lever (or put the clothes peg back onto the drain hose of the home made fuel pressure test kit) and start the engine.


Initially the fuel pressure when the engine is cold will be at about 3.0 bar and should drop to about 2.5 bar as the engine warms up.


Here is what the fuel pressure looks like on my car when the engine has warmed up:-




Now disconnect the vacuum hose to the fuel pressure regulator from the inlet manifold end.†† The pressure should now rise to 3.0 bar:-


Now switch off the engine.The fuel pressure should now slowly drop and should be at least 2.0 bar 10 minutes later:-





Now reconnect the vacuum hose back onto the inlet manifold.


If the fuel pressure doesnít drop at all or the fuel pressure drops below 2.0 bar then the fuel pressure regulator must be replaced.


Note: On the Sealey fuel injection pressure test sets 100 kPa = 1 bar.