Causes of Excessive Carbon Monoxide

High carbon monoxide levels are caused by anything that can make the air/mixture richer than "ideal". The following examples are typical causes of rich mixtures on fuel injected vehicles:

• Excessive fuel pressure at the injector(s)

• Leaking fuel injector(s)

• Ruptured fuel pressure regulator diaphragm

• Loaded/malfunctioning EVAP system (two speed idle test)

• Crankcase fuel contamination (two speed idle test)

• Plugged PCV valve or hose (two speed idle test)

• Closed loop control system incorrectly shifted rich

• False input signal to ECM

-incorrect indication of load, coolant temp., O2 content, or throttle position

Note: It should be pointed out that due to the reduction ability of the catalytic converter, increases in CO emissions tend to reduce NOx emissions. It is not uncommon to repair a CO emissions failure and, as a result of another sub-system deficiency, have NOx increase sufficiently to fail a loaded-mode transient test.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

Don't pay hundreds of dollars to find out what is wrong with your car. This book is dedicated to helping the do it yourself home and independent technician understand and use OBD-II technology to diagnose and repair their own vehicles.

Get My Free Ebook


Post a comment