Expert Advice, October 2002 edition

Questions and answers from the Truck Trend Garage

Alex SteeleOct 23, 2002
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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.
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2002 GMC Sierra 2500HD transmission inquisition
Q: I have an 2002 GMC Sierra 2500HD pickup Duramax diesel and the Allison five-speed automatic transmission. I have three questions: (1) Based on the articles in your magazines and the brochures from GM, it appears the Grade Braking function in the Allison is only supposed to work in the Tow/Haul mode. On a recent trip in the mountains driving in the normal mode, the transmission downshifted on several occasions while descending on long downhill grades at 60-65 mph after the brakes were applied. Has this been changed in the newer models to work in the normal mode as well as the Tow/Haul mode? (2) It appears that, when accelerating, the torque converter locks up after the transmission has shifted to fifth gear in the normal mode and locks up when it shifts to second in the Tow/Haul mode. Is this correct? (3) Is the transmission locked out of fifth gear when in the Tow/Haul mode?
A: We contacted Allison Transmission and went over the details of the functionality of the Allison 1000 series transmission currently used on Chevy & GMC HD truck applications. The answer to your first question is "no," nothing has been changed and the Grade Braking is available only in Tow/Haul mode. However, the system's control modules look at such data as rpm, vehicle speed, and brake-pedal position to determine if you're traveling on a significant decline. It'll then automatically downshift and supply engine braking to slow the truck, a process done manually on most other automatic transmissions. But there was a glitch when GM installed the five-speed Allison 1000 as an option replacing the four-speed Hydra-Matic 4L80-E Transmissions. It stayed with the four-speed-shift quadrants along with the original Transmission Position Sensor and indicators that display only four forward gears D-3-2-1. This prevents you from manually putting the transmission into fourth gear to provide engine braking. To alleviate that problem, engineers enabled the automatic 5-4 downshift in the normal mode under certain conditions. They're working on providing another method for manual fourth-gear engagement on future models. Next question: The Lock-Up Torque Converter, which locks the engine directly to the transmission when certain conditions are met, will be applied in normal mode once the transmission is in fourth gear (not fifth) and the engine loads and vehicle speed are within certain parameters. When in the Tow/Haul mode, which provides beneficial shift quality when towing or hauling significant loads, the torque converter will be able to lock up in, as low as, second gear. This also helps with shift quality while keeping transmission oil temperature down. Last, fifth gear is fully functional in the Tow/Haul mode, but it may require higher speeds before engagement.
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Reading 1997 1500 Dodge Ram trouble codes
Q: I have a 1997 1500 Dodge Ram with the 5.9L engine. It cranks for a long time (6-10 sec) before it starts. It starts up fine unless it sits for five minutes or more. The check-engine light comes on and goes off every once in a while. The codes are 12, 21, and 55. I've replaced the fuel pump, spark plugs and wires, camshaft position sensor, and the battery.
A: It's easy pulling up the trouble codes without a scanner on your Dodge Ram. Cycle the ignition key On - Off - On - Off - On within 5 sec, and the codes will start flashing from the instrument panel. The extended crank and the trouble-codes may or may not be two separate issues, but the codes are certainly the best place to start. We looked at the Dodge trouble code charts and found that the Powertrain Control Module has lost direct battery input within the past 50 times the ignition was turned on. This code will not illuminate the check-engine light and may have been set when you replaced your battery. Code 55 flashes to inform you that all the stored trouble codes in the PCM's memory have been displayed. The code 21 is the actual problem to look into concerning the oxygen-sensor circuits. Your truck uses an upstream and a downstream O2 sensor. This means one is mounted in the exhaust system before and after the catalytic converter in order to determine if the Cat is doing its job. Chances are that one of the O2s has failed, but it's going to require an experienced technician with the proper scan tool and the appropriate service information to make a without-a-doubt diagnosis. The cause can be either a sensor or a problem elsewhere in the oxygen sensor to PCM circuitry. Again, the hard-start condition is often fuel-pressure related and may have a different cause altogether.
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2001 Nissan Frontier 4x4 needs supercharged diagnosis
Q: I own an 2001 Nissan Frontier 4x4 with the supercharger and 50,000 miles on it. I brought it to the dealer for an oil change, and while driving to work I heard a clanking sound coming from the engine. I opened the hood and noticed the antifreeze overflow was bone-dry, so I brought it back to the dealer; the mechanic said the noise was from the supercharger, and when it warms up it will go away. Even when the truck is warmed up I still hear the noise when stopped at a light. Is this common for a supercharger or is the dealer pulling my leg?
A: The Frontier pickup with the supercharged 3.3L V-6 has been out for only a few years in a small volume of production, so all reliability issues involving the supercharger may have not yet come to the surface. I've asked several members of various Nissan service departments what sorts of complaints they've received involving the forced-induction Nissan, and there seem to have been very few at this time. It's true that some superchargers will normally emit a rattling type noise at idle. But the new Frontier SC I road tested when they first came out was fairly quiet, aside from the normal supercharger whine on acceleration. The Nissan 3.3L engines have an inherent lifter clatter on cold startup that disappears once oil pressure reaches the hydraulic valve lifters; this should be considered normal. I mention this in case it's part of the noise you're getting on startup. The technician changing your oil shouldn't have let you go with an empty coolant reservoir. Your best bet is to take it back to the service department in order to reevaluate the noise and perhaps compare to another supercharged Frontier. At this point, a noticeable noise at idle when hot does warrant further investigation.
Excess 1997 Ford Ranger Drip
Q: My 1997 Ford Ranger has been having a problem in high-humidity weather: Condensation is dripping on the passenger-side floor when the A/C is on. I brought it to my mechanic, and he thought the evaporator drain must be clogged. He said that he blew compressed air through it and it should be clear, but I still have the problem and the condensation is also dripping out under the truck just like it's supposed to.
A: Ford has come out with a Technical Service Bulletin pertaining to this problem and there is a fix for this misrouted condensation condition. As we know, a large amount of water condenses from the humid air as it passes through the cold evaporator core part of the A/C system within the dash. The water then drips off the evaporator and into the bottom of the plastic evaporator housing. From there, it makes its way to the street via the evaporator drain tube that passes through the firewall. The problem in some 1997-1998 Rangers, Explorers, and Mountaineers, along with the 1999 Super Duty trucks, is a leakage of moisture-rich air around, and not through, the evaporator core. This air delivers condensation further into the heater plenum and duct work, which is not designed to drain off the condensed liquid. That's why water ends up on your passenger's feet. The recommended repair is a decent size job that involves the removal of the evaporator and a detailed positioning of a new evaporator seal. This is to make certain that all incoming air must pass through the cooling fins of the evaporator core while leaving no pathway for air to bypass the core and reach the heater plenum. The Ford dealer can help you out, and it may be expensive if you don't have an extended warranty.
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.

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