Expert Advice July/ August Edition

Getting the Good Gas
Q: I recently bought a 2006 Jeep Grand Cherokee, and the base where I'm stationed in Yokosuka, Japan, only has 93-octane gasoline. The Jeep owner's manual recommends 87- or 89-grade gasoline for optimum performance. Will 93 grade hurt the engine?

A: Higher-than-recommended-octane fuel typically gives two results: a small or negligible gain in power and/or fuel economy, and a significant waste of cash at the pump. I don't know of any official studies, but I've heard talk about higher octane than necessary producing extra carbon buildup within the combustion chamber--that takes up space, raises compression, and may cause the engine to really need a higher-octane fuel. Again, there's no proof. Don't worry. Use the 93 octane and add a gas treatment periodically to keep the combustion chamber clean--just in case.

Ford Diesel Troubleshooting
Q: My 2003 Ford F-250 turbodiesel won't start in the morning unless I hold a gas-soaked rag over the air duct. Once I do that, it starts with a bad knocking noise for about five minutes and is okay for the rest of the day.

A: The more ignitable gasoline vapor from the rag (just like starting fluid) is treating the symptom, not the cold-start problem. The induced startup is followed by some nasty knocking as the high-compression diesel engine wolfs down the wrong fuel for breakfast. Don't mess with this one. Get it to a qualified independent diesel technician, or better yet, a local Ford service department. Diesel problems can be even more difficult to identify than those of their gasoline-powered counterparts. A technician will plug in a scan tool to check for related trouble codes, while analyzing pertinent data. Depending on what's found, there may be a long list of areas to cover after that. The 2003 model-year 6.0-liter Power Strokes had a number of driveability issues that may include a hard- or no-start condition while cold. Fuel pressure, fuel contamination, and fuel-injector problems are high on the list, along with glow plugs not working correctly. Unlike a gasoline engine that uses a spark to ignite the air/fuel mixture within the combustion chamber, a diesel uses much higher combustion-chamber pressures to initiate the explosion. It just needs warming up by the electrically powered glow plugs that protrude into each cylinder. There's a known problem with poor connections at the glow-plug control module. The fuel-injection control module, or shorted wiring thereof, also can cause trouble. And it's always important to keep the entire system up to date with the latest software calibrations. A good technician will read through all of Ford's TSBs related to the condition. He'll probably even have a few memorized.