Smoking out the rough idle and stalling of Expedition

  • Article by: PAUL BRAND
  • Updated: January 18, 2014 - 5:26 PM

Q: 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?

A: 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.

Q: 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 2½ quarts of engine oil between changes. The service writer at the Toyota dealership tells me that 1 to 1½ 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.

A: 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.

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