More Power for Expeditions
Q: My 1999 Ford Expedition has the 5.4-liter engine and 103,000 miles. It's only used for hunting and fishing, often pulling a trailer. The engine's a bit short on power with even a medium trailer and often downshifts to second gear at 70 mph. Overdrive is almost out of the question. Even reducing speed is of little help. Of course, fuel use is extreme. Would a custom lower-restriction exhaust and a programmable chip help? Is chip programming safe for the engine?
A: I don't know how heavy your "medium" trailer is, but 70 mph in second gear isn't a good place to be, regardless. There are lots of aftermarket exhaust systems, intake ductwork, filters, and control-module programming alternatives, and they all illustrate impressive before and after performance graphs. But installing the products and then adding up the promised horsepower and torque with a calculator rarely agrees with the dynamometer. A 1999 Expedition with over 100,000 miles on the clock used for hunting and fishing may not be the best place to invest in performance parts, which may end up disappointing you. With 260 horsepower pushing a heavy full-size SUV, Ford's 5.4-liter V-8 was no Hercules to begin with. It was revived in 2005 with a 40-horse boost thanks to new three-valve cylinder heads. Have the sport/utility gone over from head to toe. Maybe there's a mechanical issue slowing you down, such as an obstructed catalytic converter, transmission problems, or inadequate fuel delivery. A dirty mass airflow sensor also can produce some strange symptoms.
Bad Suburban Vibrations
Q: My 1998 Chevy Suburban has a vibration that feels like the U-joints are bad. I've had the driveshaft balanced, installed new U-joints, rebuilt the front end, replaced the tires, checked and balanced the wheels, and tried new wheels. Besides having paid a fortune for all these unsuccessful fixes, I've paid a fair amount for wrong diagnoses as well. I bought it used with 70,000 miles. It now has 130,000 and the problem has always been there.
A: Typically, you can narrow the source of a vibration to the driveline if the vibration disappears after shifting the transmission into neutral at speed. Also, that the vibration is most notable during acceleration tends to indicate the driveline. One item you didn't mention, which can produce a driveline vibration, is the ride (trim) height being out of whack. There are specifications for your Suburban requiring measurements taken from exact points at the suspension and frame. This is to determine that the vehicle's suspension is holding the chassis at an optimal height off the ground (front and rear). When the ride height is correct, the suspension and driveline will sit at their most efficient positions. If the height is incorrect, the driveshaft can be situated at excessive angles in relation to the transmission and/or rear axle. This will result in a driveline vibration, or a wobbly feel while giving it gas. Ride height out of specs can be caused by weak or broken springs, misadjusted front torsion bars, or damage from a collision. You also want to be sure the driveline is in a straight line and not knocked out of position from side to side--again, possibly from chassis damage. Additionally, there may be a broken transmission or engine mount, loose crossmember, transmission not bolted securely to the engine, and so forth.