Causes of Excessive Hydrocarbons

As mentioned, high hydrocarbons is most commonly caused by engine misfires. The following list of problems could cause high HC levels on fuel injected vehicles. As with any quick reference, there are other less likely causes that may not be included in the list. Here are some of the more common causes:

• Ignition system failures

-faulty ignition secondary component

-faulty individual primary circuit on distributorless ignition system -weak coil output due to coil or primary circuit problem

• Excessively lean air/fuel mixture

- leaky intake manifold gasket

- worn throttle shaft

• Excessive EGR dilution

- EGR valve stuck open or excessive EGR flow rate

- EGR modulator bleed plugged

• Restricted or plugged fuel injector(s)

• Closed loop control system incorrectly shifted lean

• False input signal to ECM

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

• Exhaust leakage past exhaust valve(s)

- tight valve clearances

- burned valve or seat

• Incorrect spark timing

- incorrect initial timing

- false input signal to ECM

• Excessive combustion blowby

- worn piston rings or cylinder walls

• Insufficient cylinder compression

• Carbon deposits on intake valves

Was this article helpful?

0 0
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