Starting in 1996, automotive manufacturers began equipping all new cars with
a new federally-mandated emissions diagnostic system called On-Board
Diagnostics, or ODB-II. An earlier version, called OBD-I is
implemented on 198X-95 BMWs, but is not as advanced or easy to tap into as
OBD-II. For more information on reading Fuel Injection fault codes on
the OBD-I system, see the
Article, Reading Fuel Injection Fault Codes. The OBD-II system was
developed primarily to help combat emissions problems by quickly and easily
identifying failed components of the fuel injection system.
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
software has several different screens that allow you to monitor the system
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.
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 youre 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. Its 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.