Reading OBD-II
Fuel Injection Systems
Wayne R. Dempsey

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     In the past, it was prohibitively expensive to purchase the equipment required to read and process the information from the OBD-II interface.  However, scanning tools and software has come down significantly in price, enabling just about any home mechanic to read, record, and monitor the entire fuel injection system.  There are many scanner tools available today, and quite a few that allow you to monitor the OBD-II interface on a laptop computer, or even a PocketPC.  These scan tools save you time and money by allowing you to diagnose potential problems without repeatedly taking your car to your local mechanic or dealer.  I have heard people gripe and complain about how today's modern cars have become so complex that the average do-it-yourself mechanic can't figure out what's wrong with the car.  I don't buy into that - the OBD-II cars are much easier to diagnose and repair than earlier models primarily because the computer will tell you exactly what is wrong and takes the guesswork out of complicated troubleshooting.

     For my own garage, I chose the laptop-based software from AutoEnginuity, available from Pelican Parts.  The package comes complete with an OBD-II adapter, a serial cable, and software that is installed on your Windows laptop computer.  Installation and setup is very easy and is as simple as plugging in the connector and cable into your BMW's OBD-II port.  The OBD port is located near the driver's foot well, on the lower left side (Figure 1).  Simply flip open the cover, pull off the plastic connector cover, and plug in the adapter.  Run the cable over the steering wheel and plug it into your laptop, which can fit on the passenger's seat (Figure 2).

     The AutoEnginuity software has several different screens that allow you to monitor the system in real-time.  Figure 3 shows the live data screen, which can be customized to show any one of the OBD-II sensors.  You can output oxygen sensor voltages, engine RPM, coolant temperature, ignition timing advance, intake air temperature, or a host of other sensor values.  The software allows you to capture and freeze the data or log it to your local hard drive.

     Figure 4 shows the Dashtop screen, which allows you to monitor various sensors in a analog format.  This is very useful for when you are driving, and you want to quickly glance at the "gauges" to get a quick idea of what their values are.  This screen functions very similar to the sensor screen with the digital readouts.

     The live data graph screen is shown in Figure 5.  This allows you to monitor two sensors side by side, and graph their changes with respect to each other.  This particular screen is very useful for tracking down intermittent failures and can be set to run for extended periods of time while you're attempting to recreate the problem.

     There is a separate screen specifically tailored to monitor your oxygen sensors (Figure 6).  The oxygen sensor (also known as the O2 sensor) is probably the best indicator of your engine's health and performance.  The oxygen sensor changes its value based upon the amount of oxygen present in the exhaust.  This percentage is directly related to the air/fuel mixture that is fed into the engine's intake manifold.  If the mixture is too rich or too lean, the engine will not generate an ideal fuel burn.  This results in increase emissions, and a decrease in power.

     The OnBoard test results screen (Figure 7) shows the results from several diagnostic evaluations of various system modules.  The system monitors the engine in real-time for misfires, fuel compensation, and comprehensive component monitoring.  The results of the tests are shown on the right.

     In addition to the full capabilities of the OBD-II scanning software, the AutoEnginuity package includes a neat tool call SpeedTracer. This utility allows you to estimate various performance characteristics of your BMW by monitoring the sensor output from the OBD-II computer. In real-time, the software acquires the engines RPM, the car's speed in MPH, and the ambient temperature. Mixing that with known characteristics of the car from pre-configured profiles stored within the software, the computer can accurately estimate performance characteristics like horsepower and torque. Using the real-time monitors, the software can measure 1/4 mile times and speeds as well as 0-60 MPH performance. All of the stock OBD-II compliant BMW cars are already pre-profiled in the software.  In addition, you can enter compensation variables into the software (temperature, humidity, altitude), to help correct the horsepower results to ensure accurate and repeatable results.  If you have modified your BMW, you can change the default values specifically to fit your car.

     The SpeedTracer tool is definitely a fun tool to play around with. However, like the big roller dynos, the horsepower figures are somewhat subjective.  Driving ability and habits and may slightly skew results in the software.  As with the traditional dyno, SpeedTracer is best viewed as a comparison and tuning tool.  Although not as precise as a real dyno, you can test your car indefinitely, and use it to determine if you’re gaining any horsepower from minor modifications and tweaks.  As with the big dyno, the results are often dependent on environmental factors, so you should only really compare numbers from same-day runs.  It’s also highly dependent on the characteristics of your driving, including the speed at which you shift through the gears. Another downside, of course is that you need a laptop computer to make the whole system work.