Smoking out the rough idle and stalling of Expedition

I have a 2001 Ford Expedition with the 5.4-liter V8 and 103,000 miles. At 98,000 miles it developed a rough idle and began stalling at stop signs.

My local mechanic noticed low fuel pressure and replaced the fuel filter and fuel pump. It ran good but then the "Check engine" light came on and the rough idle and stalling returned. The mechanic could not find anything wrong but a scan found codes P0171 and P0174. Another mechanic came up with the same codes and checked for vacuum leaks but could not find any. I have continued to drive the vehicle and the "Check engine" light is still on. Any suggestions?

My Alldata automotive database confirmed that the P0171 and P0174 codes indicate a lean fuel/air condition from both cylinder banks. Since technicians have checked for but not found the problem, I'd suggest a "smoke" test to help identify any vacuum leaks. This simple test involves introducing a non-toxic smoke into the crankcase under low pressure and then watching for any smoke escaping from the engine, induction system or vacuum lines.

Also, a ruptured diaphragm in the fuel pressure regulator, located on the fuel rail downstream of the fuel injectors, could cause low fuel pressure as well as fuel leakage directly into the intake manifold. If there's
liquid fuel in the vacuum line at the regulator, the diaphragm is ruptured. Rough idle and stalling at stops are often symptoms of a failed fuel pressure regulator.

I own a 2008 2.4-liter four-cylinder Toyota Camry with 98,000 miles that I service every 5,000 miles. For the past 15,000, miles I have had to add 2 to 2 1⁄2 quarts of engine oil between changes. The service writer at the Toyota dealership tells me that 1 to 1  1⁄2 quarts every 5,000 miles is normal for these aluminum engines. I have not noticed a decrease in engine power or any smoke from the tailpipe. I bought this car new expecting to get 200,000 miles out of it. I think this is a lot of oil for a car to burn.

One quart per 2,000 miles is completely within Toyota's "normal" oil consumption guidelines of one quart per 1,200 miles. Your concern is due to the change in oil consumption. Has oil use continued to increase? Or is it stable at this rate? Unless or until the consumption rate increases to excess, I would not be particularly concerned.

Unless oil use is being caused by a clogged PCV system or "sticky" piston rings, there's no easy "fix." You could try de-carbonizing the rings/grooves to free any sticking rings that could increase the amount of oil reaching the combustion chambers. Remove the spark plugs after shutting down the hot engine and pour an ounce or so of SeaFoam directly into each cylinder. After an hour or overnight, temporarily disable the ignition and fuel injection and crank the engine to expel any liquid in the cylinders. Reinstall the plugs, re-enable the ignition and injection, then start and drive the vehicle for at least 20 minutes.

I use "high-mileage" oil and change it every 3,000 miles on my two high-mileage cars. What kind of oil should I use when topping up the oil between changes during this very cold weather? Would 0W-20 full synthetic be the best bet? What is your opinion on using 0W-20 full synthetic for the regular oil changes during the cold months?

When adding oil between oil changes, use the same brand/viscosity already in the crankcase. Adding a different oil isn't harmful but the additive package and viscosity are likely not the same. I don't think 0W-20 would be a good choice in high-mileage vehicles unless the carmaker suggests it in the service recommendations. For most modern engines a full synthetic 5W-30 would be a good choice in cold temperatures.

Paul Brand, author of "How to Repair Your Car," is an automotive troubleshooter, driving instructor and former race-car driver. Readers may write to him at: Star Tribune, 425 Portland Ave. S., Minneapolis, Minn., 55488 or via email at paulbrand@startribune.com. Please explain the problem in detail and include a daytime phone number.

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