2000 Toyota Tacoma pickup with noise at speed
Q: I own a 2000 Toyota Tacoma pickup truck (2.7L) with 32,000 miles. For the last 12 months, I've been hearing a squealing noise coming from somewhere in the rear. I drive 25 miles each way to and from work and travel at mostly highway speeds, about 60 mph. The noise is irregular in tone and seems to occur when I'm going downhill and take my foot off the gas pedal. When I step on the gas again, the noise disappears. It appears to come in phases: Some months and weeks, I'll hear it every day, then it'll go away for several weeks or even months. It happens in any weather or temperature. However, it starts when I've driven at highway speeds for 10-15 minutes. I never hear it when I drive around town. I've taken it back to the dealer four times, but they've been unable to locate the source. Right now, I'm in a period when the noise has gone away, but I know it'll come back again when I least expect it to.
A: Initially, it sounds like the squeal you're describing may have been a gear whine from the rear-axle assembly while coasting downhill. That would explain the noise coming and going as you take your foot off and on the gas. The only trouble with this theory is that noisy ring and pinion gears don't go away by themselves. It's possible the noise is more noticeable after you've driven for a significant period of time and created a situation where the oil in the rear-axle assembly reaches a certain temperature, which allows the noise to become more pronounced. The next time you hear the squeal, take note of the surrounding conditions. What speed you're traveling, what gear the transmission is in, accelerating or decelerating, engine rpm, how long and how many miles you've been driving, up or downhill, and, most important, where you are. I've seen on more than one occasion where terrible noises occur in only one particular location. It may have nothing to do with the vehicle itself but just an obnoxious sound transmitted from the tires on an oddball road surface. Your Tacoma's noise can be originating from a number of other areas that require a qualified technician to hear it before diagnosing the problem accurately. So, take notes, and stop by the dealer to take a tech for a ride the next time around.
2001 Silverado 2500 4x4 wants more power
Q: I own an 2001 Silverado 2500 4x4 with extended cab and 3.73:1 rearend. It's rated at 300 hp and 360 lb-ft of torque. While my truck has great power and performance, I note other GM models have this engine with higher power ratings (Sierra C3: 325 hp; Yukon Denali: 320 hp; and Escalade: 345 hp). Can you identify what GM has done to increase the power for these versions of the Vortec 6000 engine? I tow a 29-ft fifth-wheel trailer weighing 7700 lb, and while my truck seems to handle the job well, I wonder if there are some simple and relatively inexpensive things I can do to increase its power?
A: All the vehicles you've mentioned, with the exception of the Cadillac Escalade, utilize the Vortec 6000 LQ4 V-8 engine. The Caddy SUV is actually fitted with the Vortec HO 6000, option code LQ9, and uses a higher compression ratio, via a piston upgrade, which brings it up from the LQ4s 9.4:1 to a 10.0:1 ratio. This explains the significantly higher power rating of 345 hp at 5000 rpm. The Vortec LQ4 engines in the other 1/2-ton GM light-duty trucks, such as the Sierra and the Yukon, only have a slight horsepower variance. The plus or minus five horsepower is due to the different exhaust systems and air intake configurations in each model. Now here comes the tricky part. Your Silverado 2500 is considered a heavy-duty truck due to vehicle weight and therefore falls under certain federal regulations, one of them being the Transportation Equipment Noise Emission Controls. There was a problem with the Chevy and GMC 3/4- and 1-ton trucks equipped with the 6.0L V-8 engine producing excessive noise. Your truck's LQ4 engine actually had its potential horsepower downgraded. It now peaks at 300 hp at 4400 rpm because it was too noisy and would have failed the test pushing more horsepower at a higher rpm. According to the General Motors Engineering Communications Department, there were also driveability concerns involved with the decision, and the downgrade was accomplished through various means including the programming of the powertrain control module. One of the experts in GM performance reprogramming is Fastchip. You can log-on at www.fastchip.com or give them a call at 918/446-3019 for further details. You can pick up the K&N Generation II Fuel Injection Performance Kit to aid intake airflow for a few more horses. I also suggest not putting any money toward exhaust modifications on the 2500 series. The factory setup appears to have a good flow, and aftermarket performance systems are showing little or no advance in power.