Disconnected fuel injector creates leaner condition than disconnected spark plug on that cylinder.
Total fuel trim ~ +24% (2000 Lexus RX300 with a wideband O2 sensor)
Total fuel trim ~ +20% (2004 Dodge Neon with a narrow band O2 sensor)
Disconnected spark plug in one cylinder creates less lean condition than disconnected fuel injector.
Total fuel trim ~ +8% (2000 Lexus RX300 with a wideband O2 sensor)
Total fuel trim ~ +7%-8% (2004 Dodge Neon with a narrow band O2 sensor)
Rev the engine to 1500 to 2000 RPM and hold it steady for half a minute or so. If the fuel trim readings do not change much, the lean fuel condition is more likely due to a fuel delivery problem  than a vacuum leak.
Rule of Thumb. With fuel related misfire,  STFT goes more than 15 percent positive, often into the mid 20 percent range or more and the downstream O2 voltage below 350mV (lean).
At WOT front O2 has to show above 900mV to indicate a good fuel supply to the injectors. Below 100mV can indicate fuel supply problem as well as bad MAF.
Bad fuel supply would have good VE and lean front O2 sensors.
Excessive Fuel Flow
Fuel pressure regulator stuck closed
Leaky fuel injector
Excessive fuel pressure
Bad pressure regulator
Restricted fuel return line
Raptured fuel pressure regulator diaphragm
Leaking EVAP Purge solenoid
PCV leak (fuel or oil vapors) ???
Weak Fuel Flow
Wrong / bad fuel (e.g. E85 instead of E89)
Fuel pump (weak or non-operational)
Restricted fuel filter
Leaky fuel pressure regulator
Injector flow (sticking or not opening)
Fuel Composition
High ethanol/alcohol content?
GM. If live data shows âalcohol contentâ around 27%, try to do âFuel composition resetâ using Tech2. It should be close to 1%.
Fuel Pump Testing
Fuel Pressure Gauge (low pressure side)
 Connect fuel pressure gauge. Look at the  fuel pressure specs and compare it.
 When starting the car, pressure should build up to specs values quickly.
 With open throttle, fuel pressure should increase (like 10psi). If it deceases, fuel system has a problem, i.e. bad fuel pump. If car has pressure regulator with vacuum line, take off vacuum line to simulate wide open throttle.
 After releasing the throttle, pressure will drop lower than it was at idle, and then quickly stabilize back to specs. Its due to high vacuum at decel event.
Downstream O2 Sensor
As the fuel volume drops off and the system goes lean the downstream sensors will go lean as well. Because both banks will be similarly affected you can rule out a single cylinder concern as the cause of the lean running condition.
High Pressure Fuel Pump Testing
Use oscilloscope and fuel rail pressure sensor. If you know how many plunger does the fuel pump have, and the speed at which it turns, you can see if one pumping is missing (IATN).
Fuel Injector Testing
Balance Test
Connect a fuel gauge or pressure transducer.
Pressurize the fuel system.
Make sure that the fuel pressure stays steady.
Operate each injector by a scanner or manually and record a pressure drop.
Ideally, each such injectorâs test should show the same pressure drop.
A variation of 2psi or more is a cause for concern.
Waveform Analysis
Oscilloscope connection
Black lead â chassis ground;
Red lead â injectors pulse ground.
Current
As a rule of thumb, injectors draw around 950mA
Shorted injectors will have a steep rising ramp
Lower than normal current ramp
Bad injector
No current ramp
Bad Control Module
Bad connection
Injectorâs Power Feed
On some vehicles, you need to crank the engine to turn injectors relay ON, otherwise it will be OFF.
Injectorâs Ground Level
Look for a little raise in ground voltage at ON time due to raising current
Pulse
On running engine pulse usually within a range of 3-5ms.
During cranking it may be 20ms or higher.
Duty Cycle.
On most vehicles at idle the duty cycle is 2.9% â 3%.
Clean switching (OFF/ON/OFF)
Pintle Activity
Look at current waveform to see pintle opening
Should open at the same place all the time, otherwise may be intermittently sticking
Look at ground side voltage to see a pintle closing
Should have a little notch/hump at the downward slope after EMF spike
Fuel flow (with the help of a pressure transducer hooked to the fuel rail)
