Q: I have a 2004 Honda Pilot with 92,000 miles. Over the past year or so, I hear a momentary (1 to 2 seconds) whirring/rumbling/vibration noise that appears to come from the front of the car. It only occurs between 35 and 50 mph and happens with the A/C on or off. I have checked every piece of plastic air dam to make sure everything is secure but still get the noise. You never know when it will occur, rough road, smooth road or just randomly. All the CV boots are intact. I took it to the dealership and took them on a 15-minute test drive but could not get it to make the noise ... then got it on the drive home.
A: Honda has a whole list of possible causes. Checking them in my ALLDATA automotive database, I find several service bulletins addressing wind noise. Honda has a very interesting suggestion for trying to duplicate the noise — aim an electric leaf blower at the vehicle. If your vehicle is fitted with an accessory hood deflector, a missing or damaged rubber gasket or out of adjustment mounting bracket may be the cause. And check the rubber inserts for the roof rack crossbars to make sure they completely seal the attachment points at the end of the crossbars.
As far as possible mechanical issues are concerned, Honda says that a hissing-like sound between 30 and 50 mph, often sounding like wind noise, may be coming from the driveshaft center support bearing. They suggest that removing the driveshaft for a test drive may help confirm if this is the problem. If it is, the driveshaft needs replacing.
Q: I have a 2005 Chevy Trailblazer. While sitting at a stoplight the RPM slows way down to the point that it is going to kill on me. Then all of a sudden it will rev up to where it should be and seems fine. This also happens while driving in slow-moving traffic. Any ideas what it could be?
A: Sagging idle speeds while stopped are often caused by excess fuel being delivered to the engine. A ruptured diaphragm in an underhood-mounted fuel pressure regulator can allow engine vacuum, which regulates the regulator, to draw raw fuel into the engine. In your vehicle, the fuel pressure regulator is a spring-balanced diaphragm unit mounted in the fuel pickup assembly in the fuel tank.
Start by having a shop or dealership scan the ECM for fault codes. If none are found, have the shop safely connect a fuel pressure gauge to the fuel pressure test fitting under the vehicle near the fuel filter. Monitor fuel pressure with the key in theON position but the engine not running — it should be 50 to 57 psi. After turning off the key, the fuel pressure should not drop more than 5 psi in one minute. If the fuel pressure is low or drops quickly, the fuel pressure regulator or a leaky or low electrical resistance — significantly less than 12 ohms — fuel injector might be injecting too much fuel per open cycle.
At road speed this excess fuel may not create a symptom, but might well reduce fuel mileage. At idle and low engine speeds, however, this excess fuel can significantly influence idle speed and stability. Oxygen sensor feedback in "closed loop" may allow the computer to reduce fuel injector open time to compensate, but may not have enough range of adjustment to completely cover the excess fuel.
Motoring note: Here's a fun question to ponder ... do engines kill? Or do they die? I frequently hear from readers that the "engine killed on me" in describing a driveability problem. And I always wonder, "What did it kill?"
I've had engines die on me many, many times — including several on-track complete engine failures — but none of them ever killed anything! Comments?
Happy holidays, buckle up and drive safely.