GM Tech Tip: Black Smoke And Rough Idle On Cold Start -

GM Tech Tip: Black Smoke And Rough Idle On Cold Start

Working on a 2009-2014 GM vehicle? Here's what to do about black smoke and rough idle on a cold start.

Models:

  • 2009-2014 Buick Enclave and Lacrosse
  • 2013-2014 Cadillac ATS, XTS
  • 2008-2014 Cadillac CTS, SRX
  • 2008-2011 Cadillac STS
  • 2010-2014 Chevrolet Camaro
  • 2009-2014 Chevrolet Equinox
  • 2012-2014 Chevrolet Impala
  • 2009-2014 Chevrolet Traverse
  • 2009-2014 GMC Acadia
  • 2010-2014 GMC Terrain
  • Note: With 3.0L LF1, LFW and 3.6L LLT, LFX, LF3 engines only.

Condition:
The driver will complain that during a cold start black smoke will come from the exhaust and the engine will have a rough idle and minimal misfires.

Cause:
With the introduction of direct fuel injection systems, GM has revised the cold start control system to reduce cold start emissions. Quicker catalytic converter heating helps meet the ever-changing emission requirements and improve fuel economy.

A dual-pulse injection strategy is utilized during engine cold start to reduce the time required to bring the catalytic converter up to operating temperature. This split injection strategy lasts for about 60 seconds on cold start. This process will cause the customer to see increased black smoke, soot, rough idle or minimal misfires during cold start and should be considered normal.

To verify that the dual-pulse injection is causing the roughness or misfires with no codes set, you should watch injector pulse width with the scan tool during the concern. Dual pulse injector pulse width will be nearly double that of normal idle.

If the pulse width on the injectors drops by about 50% and the engine then smooths out, this is considered normal operation and no repairs should be attempted. The use of TOP TIER fuels lessens the rough idle condition effects during dual pulse injection by reducing the amount of carbon on valvetrain components and a more complete combustion leading to cleaner burn.

This cold start strategy is enabled upon startup after the engine has soaked for sufficient time such that the catalytic converter requires rapid reactivation.

Follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

You May Also Like

Turbocharger Topics

Turbochargers have made a comeback – and it’s been quick.

Smaller engines, greater diagnostic opportunities.

Turbochargers are not a new technology. In the 1980s and 1990s, many automakers used turbochargers on gasoline engines for performance on limited applications. Many of these vehicles got a bad reputation for reliability and power that came on in one big lump.

Transmissions – CVT

Knowing what the common issues are & understanding the options available to isolate & fix problems are the keys to success.

Fuel Pumps and Cranking

Diagnosing the problem comes down to understanding what causes a loss of fuel pressure.

Wheel Bearing Service Tips

When faced with any noise complaint, take the time to test-drive the car.

Navigating the Intricate Landscape of Coatings and ADAS

With refinish and ADAS, the theme time and time again comes back to: check the OEM repair recommendations.

Other Posts

Proper Paint Prep: Cleaning and Abrading

Nothing is faster or more profitable than doing the job one time.

How Battery Service Continues To Change

Your attention to a battery’s condition will tell you if it needs to be replaced – and with what.

Catalytic Converter Replacement Rules

The conditions under which the catalytic converter was installed is of great importance to the part manufacturer.

ADAS False Activation Evolution

The logic behind most ADAS warnings or corrections is to examine the plausibility of the situation.