Fuel Pressure Test - Tuesday 4th November 2014

Fuel Pressure Tester
(Petrol)

 We were assigned 2 different engine types for this task, one being SI and the other CI.  The SI was a Volvo S40 and the CI was a Citroen C4.  The methods of testing both differ in terms of which test equipment to fit and where, as the CI fuel system operates at vastly increased pressures to that of a SI system (SI 3-4 Bar and CI approximately 1600 bar and above).  We started by gathering all of the vehicle data for both vehicles relating to expected pressures upon testing.  The test equipment for a SI fuel system is connected to the fuel rail via a Schrader valve, and then the ignition turned one position to activate the fuel pump and bring fuel to the rail under pressure.  The reading is taken from the gauge (and monitored for approximately 30 minutes to observe any leak down) and noted on the job card.  The ignition is then fully activated and the reading from the gauge also noted and compared.  The accelerator is then "blipped" to observe any pressure fluctuations under load.

Connector fitted to
Fuel Rail Schrader Valve

In order to test a CI system a suitable diagnostics scanner (such as a Decscan or Carman) with live data reading facility must be used.  This is connected via the vehicle's EOBD port and the relevant section activated accordingly.  Results were noted and compared to the manufacturer's specifications as before.

Amps Clamp fitted to
Injector Live Feed

Having completed both tests and noted down possible causes of fuel pressure loss we were then asked to undertake an analysis of the Fuel Injector performance on the CI engine.  

This was achieved by connecting a Picoscope and monitoring the Amperage being supplied to the injector and also observing the number of pulses produced in its' operation.  This is displayed in a live data graph format and can then be compared to  a known good example contained within the software package itself.  This task remains incomplete as the data we obtained from all four injectors only produced 2 pulses, whereas the example contained within the software displays 3.  Multiple bursts are introduced as a means of evening out the combustion process and reducing diesel knock.  Further investigation required and will be resumed on Monday morning.

Example of expected pattern
from a Bosch Injector