The Exhaust Gas Analyzer
If you already possess and use a dwell/tach, compression tester and a timing light, it indicates that you're definitely an "intermediate" or perhaps "advanced." What next? What piece of equipment can you buy that will really help diagnose and tune an engine in a more professional manner?
My suggestion is an exhaust gas analyzer. Granted, experience, "feel" and a good ear will enable most competent mechanics to tune a carburetor (or carburetors) and fuel injection systems to very near optimum performance. But with today's EGR systems, it becomes more difficult. Even "de-smogged," the air-fuel ratio at idle determines whether you're running on the rich side, too lean, or just right.
Too rich a mixture can dilute your oil and eventually "wash" your cylinders, causing premature piston wear, not to mention poor gas mileage, fouled plugs and other expensive problems. Too lean, you run the risk of holing pistons and/or burning valves.
An exhaust gas analyzer won't perform a tune-up for you, but it will give you an indication of how well a job you've done. Halves must be adjusted to the proper clearances and the entire system should be in good condition, with dwell and timing adjusted to specifications. With all these variables checked, you can then analyze the air-fuel ratio and percent CO of your exhaust to determine if carburetor or Fl adjustments (or re-build) are necessary.
Having purchased and built the Heathkit Model C1-1080 Exhaust Gas Analyzer, I can attest to its ease of construction and quality. The price of just under $70 delivered has been saved in a few short months via quicker, more accurate tuning (not to mention peace of mind). If you have a soldering iron and a few basic tools, a couple of hours time will reward you with a very high quality instrument consisting of the meter, sensor, cables and a rugged plastic case with complete instructions.
Owners of air pump-equipped BMWs should disconnect the hose from the air pump at the check valve before attempting to "read" the exhaust, since this extra air will not allow you to determine the actual exhaust gas content alone. The only adverse temporary effect with this hose disconnected will be the sound of the pump and the check valve "gurgling."
Consult your owner's manual, the decal in the engine compartment, or factory shop manual to determine the permissible range of percent carbon monoxide allowed for your particular BMW.
Your chapter may wish to consider the purchase of such an item for use at tech sessions and on a loan basis to members. Perhaps two or three of you may decide to "go in on one" to minimize the expenditure. Once you've had an opportunity to use an exhaust gas analyzer, it's worth will become immediately apparent as an excellent diagnostic tool for more professional tune-ups and for furthering the joy of driving!
Author: Stan Simm