Fuel Injection: Basic Diagnosis & Repairs

The EFI system is a standard system in modern cars.  It is a big advantage in fuel efficiency technology over the old carbeurrator systems.  The EFI system is a series of sensors around the car  which send an ECU (engine control unit) signals which are processed to then control the outputs of the ECU which include fuel injectors and monitored fuel pressure levels. It had replaced the old carburetors in the 1980's and 1990's.

The electronic fuel injection system has plenty of advantages, but needs plenty of things to get this.  It is made up of a bunch of sensors that basically send signals to the ECU (Engine Control Unit), a computer that makes calculations to the signals, and then controls the signal outputs like the fuel injectors.  This means that the ECU can adjust itself to different driving conditions, styles and environments.  (I personally like to think of it as a team, where a group of people in different areas observe the engine and tell the coach what is going on, then the coach tells one of the team members how to work).  Since there are many components around the car,  there is a higher chance that something can go wrong, which can cause the engine to not run at its highest potential.  This basically means that a fault in one of the sensors will cause it to send bad signals to the ECU, which will therefore lead to bad output signals.  

There are many different types of sensors in EFI cars that include air flow sensors, oxygen sensors, temperature sensors, etc.  As a mechanic it is important to be familiar with these sensors as they all look different between different cars.  They generally work the same way so as long as we know how to test them its all right.  

We learnt how to test almost every type of sensor that you'd find in an EFI engine.  We basically used a multi meter to check the voltage or resistance signals, and we change what it is sensing (eg. Throttle position sensor,  we check the resistance of the signal while moving the throttle).  Most of them are easy to check by using a method called "back probing" the terminal at the signal.  This is done by using a pin and stabbing one beside each cable in the terminal.  This generally involves one or two cables (one being positive and one being negative).  The aligator clips on a multimeter/oscilloscope are clipped onto the pins.  We can either change the sensor by moving it (depending on what sensor it is).  Other sensors like temperature sensors are simply done by back probing it and turning the engine on, checking if the sensor changes its output signal.

When it comes to repairing in engine, it is usually easiest to gather up all the symptoms.  Things like smoke, colour of smoke, knocking sounds can be fairly obvious but to be as accurate as possible, we can use an emissions tester (I have written another post on using the emissions tester, here: http://patcat.blogspot.co.nz/2012/06/emission-control-machine.html ).  Once we have gathered up all the symptoms we can diagnose the problem by either narrowing it down to what we can think, or we can get a fault code from the ECU by either bridging terminals or using a scan tool.  We had a top of the line Snap-On scan tool which turned out to be completely useless as the guides weren't very informative, so we used a bridging method that involves bridges two small cables in the diagnosis terminal.  We used the Toyota engine and bridges E1 and TE1, turned the engine ignition on and counted the flashing of the check engine light.  The light works by flashing a number of times, pausing, then flashing a number of times to represent the second digit. (eg.  2 flashes, pause, 4 flashes = fault code: 24).  We then use these codes and refer to a great technology that we called the internet.

Sensors generally can't be repaired and can only be replaced.  A lot of the time when an engine is not running right (especially if its old or has been well used) I tend to suspect an issue with bad spark plugs.  The spark plugs aren't a sensor, but even just one faulty spark plug can cause the whole engine to not run right.  The problem occurs when the spark plug does not ignite a full fuel and air mixture, and as it escapes, the oxygen sensor reads a high content of oxygen, which tells the ECU to "richen" the mixture, which means adding more fuel to the mixture.  This will cause a rich mixture in the engine, and therefore wear out the spark plugs even more. (I actually just changed my spark plugs in my car, as my car needs long lasting 100,000km spark plugs.  I purchased a set under the boss' company name and got them for about $17ea, which is far cheaper than what I quoted under my name up to $51ea at BNT. I noticed a lot more efficiency and power.)

Old spark plugs changed at 112,000kms, past its recommended 100,000kms.  New long lasting iridium spark plugs that should last me another 100,000kms.