Fuel System - Driveability Concerns

SOURCE: Subaru Tech Tips

TITLE: Driveability Concerns

APPLIES TO: All H6 models

SERVICE TIP:

If you get an H6 vehicle in the shop with a driveability concern, i.e. hesitation, please make certain the owner is using a premium grade fuel, 91 octane or higher, in the vehicle.

With the recent increase in fuel prices, there may be some people who have dropped down a notch or two in octane ratings to save a few pennies. While this is understandable, these vehicles were designed to operate properly on a Premium grade fuel. If the owner says they are using a premium grade fuel, ask them if they tend to buy just ONE brand. If so, suggest they try another brand to see if the concern goes away. Different companies blend their fuels differently.

Understand also that it will take a few tanks of the different brand of fuel for the Engine Control Module (ECM) to "re-learn" its operating parameters on this different fuel.

If you are able to duplicate the owner's concern, we suggest you perform a "Clear Memory" function of the ECM and then road test the vehicle again. If the concern has gone away, then the most likely cause of the problem is the fuel being used in the vehicle at that time.

Another factor to take into consideration is the use of oxygenated or reformulated fuels, know as State Winter Oxygenated Gasoline. Oxygenates are fuel additives (alcohols and ethers) that contain oxygen which can boost gasoline's octane quality, enhance combustion, and reduce exhaust emissions. The term oxygenated gasoline most commonly refers to the wintertime program that reduces emissions of carbon monoxide (CO) from motor vehicles. Although required by the federal Clean Air Act, winter oxygenated gasoline programs are implemented by the states. For more information on state fuel programs go to: www.epa.gov/otaq/regs/fuels/oxy-area.pdf.