Q I have a 2000 Nissan Frontier pickup truck with the 3.3-liter engine. It has about 65,000 miles on it, and I'm getting poor gas mileage. The vehicle is rated for 19 miles per gallon on the highway, but I can't seem to get more than 16 mpg on the highway.
My son-in-law speculates that the knock sensor thinks the engine is running too lean and sends a message to the fuel injection system to richen the fuel mixture. The vehicle also is hard to start in the morning and I can sometimes smell gasoline. I tried higher-octane gas but still no mileage improvement. Do you agree?
A Your son-in-law has described the function of the knock sensor correctly, but I don't think that's the problem. An open or shorted knock sensor would be identified by a P0325 fault code, and the sensor can be checked for proper resistance out-of-circuit with a simple ohmmeter. I'd be more inclined to check for a leaking fuel pressure regulator, faulty temperature sensor or even a failed canister control valve.
Q I have a 2005 Acura MDX with 82,000 miles. It makes an unusual noise when turning or going over cobblestone pavement. The noise seems to come from the front of the car and now the back. It sounds like a basketball dribbling -- something bouncing. I suspect it has something to do with the tires or suspension. We recently had all of the motor mounts replaced and just had the tires inspected and rotated but still hear the bouncing sound.
A If a careful inspection of suspension and steering components -- specifically the shocks/struts and stabilizer links -- doesn't identify the problem, check your service records to see if the differential lubricant was changed at 15,000, 30,000 and 60,000 miles as recommended by Acura. The noise may be a ratcheting or juddering from the rear differential due to contaminated fluid, as outlined in Acura bulletin 04-023.
Q I have a 2007 Ford Expedition with 65,000 miles on it. When I brake for a slow corner and then step on the throttle, it hesitates. Instinctively, I give it more throttle, the hesitation ends and the truck leaps forward faster than I intended. At other times in stop-and-go traffic, it feels like the hesitation just before the transmission downshifts as you start up a hill. My mechanic thinks it could be a mechanical linkage problem that will be expensive to find. Do you have any suggestions?
A Because the engine and transmission are electronically controlled, I'd be more inclined to think software rather than hardware. I think you're experiencing a tip-in hesitation as you re-apply throttle. My Alldata automotive database pulled up Ford bulletin 07-8-11 that suggests updating the software programming in the powertrain (PCM) and transmission (TCM) control modules to address this problem.
Motoring note If you're into cars, the summer car-show season is in full swing. From local car shows in shopping mall parking lots to the Big Daddy of them all, "Back to the '50s" at the State Fairgrounds later this month, many of the coolest and best-looking muscle cars and street rods will be on display.
