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Truck Trend Garage: Expert Advice July/August Edition

Find out the answers to some commonly asked questions from the experts at Truck Trend.

Alex Steele
Jul 1, 2008
Downsizing For Better Mpg
Q:I have a 2001 Ford Expedition Eddie Bauer V-8 4x4 and am wondering what optimal gas mileage should be. I'm getting about 11.9 mpg, and of course would like to get better. Can you offer any advice?
Photo 2/5   |   need Better Mpgs
A:You didn't mention which V-8 is in your Eddie Bauer trim, so I'll give you the EPA fuel economy statistics for both. The 4.6-liter's original numbers were 14 mpg city/18 highway/16 combined, but dropped a point or two when converted to the new, more accurate fuel-economy testing procedure that went into effect with the 2008 model year. It's now 13 city/17 hwy/14 combined. The 5.4-liter V-8 started at 12/17/14 mpg and was updated to a more realistic 11/15/13 mpg. If you have the bigger engine and do mostly city driving, these new figures certainly make sense. I wouldn't suggest investing money on upscale performance parts in an attempt to boost fuel economy. Even if it helped a little, the parts will most likely never pay for themselves with the gas money saved, although I may retract that statement if fuel costs rise much further and performance parts don't. Focus on the basics. Keep a clean air filter in front of your engine's intake at all times; buy more than one at time when you're at the parts store. Always keep your tires filled to the correct air pressures and check them biweekly. Don't carry unnecessary cargo weight. But the best way to save fuel relies on driving habits: Accelerate and brake gradually, keeping highway speeds at 60 mph or below. Make it a project to see if you can beat the EPA estimates. Like a lot of folks are doing, you may want to downsize to a crossover if the cost of fuel is outweighing the utility space and security of a full-size SUV.
Photo 3/5   |   ford F250 Improper
F-250 Improper Downshifts
Q: I own a four-wheel-drive 2004 Ford F-250 with the 6.0-liter diesel and five-speed automatic transmission. I recently installed an aftermarket four-inch exhaust, AEM intake, and Triple Dog Power Pup Downloader. The average fuel mileage was 15 mpg, and I hoped the changes would improve that and give a significant performance increase. The power and performance gains were great, but fuel mileage never really changed. What I noticed immediately, because of the louder intake and exhaust noise, was that the transmission always shifts from fifth back into fourth gear when I take my foot completely off the accelerator, regardless of speed or whether going uphill or downhill. I've tried it at up to 90 mph and it still shifts back down to fourth when I completely take my foot off the accelerator. I thought the new chip was the problem and took it back to the dealer who removed the chip and put my truck back to factory settings, but the problem was still there. I took it to Ford and they reset everything to factory settings. It still does it. The dealer tell me nothing's wrong. Can you shed some light on the subject? Do all 6.0-liter Power Stroke automatics shift like mine, and if so, why? If not, why can't my dealer correct the problem?
A: Here's some trivia on the specific transmission bolted to your Power Stroke. Ford calls it a 5R110W, or TorqShift. It's considered a five-speed automatic based on the Ford's previous 4R100 unit. The 5R110W made its debut in 2003 model-year F-Series trucks and Excursions packing the 6.0-liter diesel. The cool part is it actually has six forward gears, but only uses five of them during any given shift cycle. When cold it shifts first, second, third, fourth, skips fifth, and goes directly into sixth gear. This takes advantage of the higher rpm in fourth instead of fifth, and delivers a quick warmup to reduce emissions and increase fuel economy. In warm mode, the 5R110W gear pattern is 1, 2, 3, skip 4, 5, 6. This pattern takes advantage of the engine's torque curve for better driveability and assists fuel economy by keeping engine speeds lower in fifth gear as opposed to fourth. (This has nothing to do with your question. I'm getting to that.) Be sure your TorqShift is actually downshifting into fourth gear when you take your foot off the gas--technically fifth if it's warm. It shouldn't downshift at all during the highway driving conditions you've described. The best way to determine exactly what gear you're in is for you and/or a technician to drive with a scan tool and read the display showing what gear is actually engaged and when. You may be hearing, feeling, and seeing an increase in rpm due to normal disengagement of the lockup torque converter, not an actual downshift to a lower gear. The torque converter hydraulically connects the engine's crankshaft to the input shaft of the transmission. So let's consider the lockup torque converter as a two-speed transmission in its own right. While cruising with the torque converter engaged, engine rpm is lower because the torque converter is locking the crankshaft to the transmission input shaft, just as if it's in Drive (or second gear). When the clutch within the lockup converter disengages, just like downshifting, the torque converter is now providing gear reduction hydraulically (first gear), therefore increasing engine rpm. The lockup converter will normally disengage when you let your foot off the gas to provide a little extra torque when you reaccelerate, and then go back into lockup shortly thereafter. Standard operation of the lockup torque converter may have become more noticeable due to a louder tone from the high-performance exhaust and/or intake ductwork.
Jeep GC Pulls To Right
Q: I bought my 2003 Jeep Grand Cherokee used with a warranty. It's pulling to the right at various speeds. I've had it in the shop and they say they can't find anything wrong. The tires look good, but could they be the problem?
Photo 4/5   |   jeep Pulls To The Right
A: Did they tell you it's not pulling, or it is pulling and they can't figure out why? There's a big difference. Believe it or not, drivers have been known to complain about alignment problems that don't exist. This is often because they're driving on a highway with a significant road crown (higher in the middle for drainage purposes); vehicles tend to drift to whichever side of the crown you're driving on. That's why a technician will either find a flat roadway or ride the center of the crown when road testing a car or truck for alignment problems. Even if the tires look fine, there could be an internal defect causing the vehicle to drift to one side, which is easy to diagnose by simply rotating the tires. If the pull is gone, either replace the tire or leave it where you rotated it to. If there's a legitimate alignment problem, verified by setting up the vehicle and taking measurements on an alignment machine, there may be extra work involved on your particular Jeep. Camber, caster, and toe are the three basic alignment angles which are adjustable on a lot of front suspensions. However, the camber and caster angles that have a direct effect on a vehicle tracking straight are fixed (non-adjustable) on 2001-2004 Grand Cherokees. And there have been cases where the cause of an alignment pull is the camber and/or caster angles being out of specification. But Jeep was kind enough to come out with special-offset upper ball joints that allow up to 1.5 degrees of camber and caster adjustment. If your Jeep is really pulling and the alignment angles are confirmed to be out of specification, install the modified ball joints and complete the wheel alignment. It may get expensive, but it's the only way to go.
Photo 5/5   |   dirty Sensors
Dirty Sensors, Dirty Engine
Q: I own a 2001 Jeep Wrangler I-6. I haven't had many problems with it until last year. The "check engine" light came on and the dealership confirmed it was the oxygen sensor. The techs told me it wasn't serious and wouldn't leave me stranded, but about two weeks ago the "check engine" light started blinking. The engine vibrated, seemed to misfire, and was slow to respond when I accelerated hard. The strange thing about this is it only happens sporadically. I changed the spark plugs and boots last weekend. My friend ran a diagnostic on the engine and came up with an oxygen-sensor error and a sporadic misfire on #2 and #6, but it misfired again this week. I've been told it's possibly an electrical problem, fuel injector, or a distributor cap or sensor.
A: The dealership confirmed a failed oxygen sensor, but you didn't replace it? Now the engine's running bad, the "check engine" light comes on, and you're asking why? Replace the sensor. A bad oxygen sensor can get to a point where it sends a false, high oxygen content signal to the computer. The computer, based on the incorrect data, will send large amounts of fuel through the injectors to richen the air/fuel mixture. This excess fuel can foul the spark plugs, cause a misfire, and make your engine run poorly. If the problem is still there following replacement of the failed oxygen sensor, then items like the ignition coils (no distributor on this one), fuel injectors, etc. need to be evaluated. Keep in mind that this engine has had issues with excessive carbon buildup on the exhaust valves, which may cause oddball multicylinder misfire conditions. This carbon buildup will require a compression test and partial cylinder-head disassembly and inspection to confirm the problem.
Drops On The Driveway
Q: My 2002 4Runner Limited V-6, which has 130,000 miles on it, leaves small drops that look like transmission fluid on my driveway. There's fluid on the bolts that hold the transmission to the engine but I'm unsure where the leak originates. What are your thoughts?
A: Best-case scenario, assuming you have an automatic and it is transmission fluid you're looking at, would be a leak from the transmission's pan gasket. Replacement is simple, inexpensive, and part of a recommended service anyway. Next up would be a leak from the front pump seal. That's where the torque converter fits into the front of the transmission. This more involved repair requires removal of the transmission and could lead elsewhere. Sometimes the bushing in the front pump, which supports the torque converter, wears out. The initial symptom is a leak from the pump seal because the converter is no longer being held perfectly straight while it rotates. A less common leak in the same area is the front pump gasket. The worst case would be a crack or porosity in the transmission case, which can get expensive. As always, we recommend proper testing before coming to a conclusion. In this case, that involves the addition of a transmission-fluid dye followed by a careful inspection with an ultraviolet light. This is a great way to spot a small leak without any major cleaning or disassembly, and you may be able to purchase an inexpensive leak test kit at a local auto-parts store.
Need Better MPG
Q:My 2004 F-150 with the 4.6-liter engine and 3.73:1 gears lost mpg when I changed tire size from 235/70R17 to 265/70R17 Fusion LT tires, hoping a taller tire would reduce rpm and give me better highway mpg. I was dead wrong. It went from 20 mpg down to 15. I bought a Predator computer programmer by Diablosport to adjust for tire size and correct the speedometer and shift points, and I used the 87-octane setting. I'm open to your suggestions. Would a 3.55:1 gear help?
A: In theory, increasing tire diameter, with all else being equal, should increase highway fuel economy. The change in final-drive ratio will reduce engine rpm at a given vehicle speed and load. At the same time, the change in ratio may hamper city mpg by increasing engine load at lower speeds. That extra oomph from smaller-diameter tires increases efficiency in stop-and-go driving. Gain a little here, lose a little there. The first number you see in a tire size (235-265) is the tire's width in millimeters, and the second number (70) is the aspect ratio--meaning the sidewall height is 70 percent of the tire's width (235-265 mm). Your upsize from 235/70R17 to 265/70R17 increased tire diameter about 1.6 inches and tire width about 1.2 inches. Increase in width adds to the tires' area of road contact, which increases friction and decreases fuel economy. Installation of tires with a coarser tread pattern also ups the ante for friction and fuel use. There are a lot of variables to consider: There may be inaccuracies in your highway mpg calculations and/or the additional width/mass/new tread pattern had an effect on any highway mpg gains from the taller tires. Installation of an aftermarket programmer to update powertrain control module software with the new tire size was the right way to go, but I wouldn't suggest spending money on new rear axle gears unless you do strictly highway driving. I'm talking nonstop 18wheeler-type highway miles. The engineers who build these trucks do their best to find a happy medium in performance and fuel economy with the appropriate specifications in gear ratios and tire sizes, while leaving a few options to fine-tune vehicles to a driver's particular parameters. That's why it's often a good idea to keep changes (tire size, axle ratio) limited to those that were available from the factory--unless, of course, you're doing hardcore off-road or performance modifications.
Choosing Your Transfer Case
Q: I'm planning to purchase a new 2008 Dakota 4x4 in the next couple months and have a question about transfer-case selection. One choice is an electronic part-time shift-on-the-fly system, and the other is an electronic shift-on-the-fly AWD system with manual lock and low range. Could you please explain the differences between the two systems including the pros and cons?
A: The NV233HD is the 2008 Dakota's standard part-time transfer case. The full-time NV244HD transfer case is available in TRX/TRX4, Sport, and Laramie trims with the 4.7-liter V-8 attached. Both units are electronically controlled by a selector switch on the instrument panel and both can be shifted while the truck is in motion (on the fly). Both units' gear selections include neutral plus 4WD High Lock and 4WD Low Lock, to be used only during limited traction or off-road conditions. The practical difference between the two units is the two-wheel-drive gear selection of the NV233HD transfer case replaced by the NV244HD's Full-Time 4WD High. Full-time means you're powering all four wheels but can drive on normal road surfaces and/or loose terrain without breaking anything. Part-time lock describes the front and rear driveshafts being locked together and turning in unison. This is great for traction on loose ground where the wheels can break free easily, but can bind the drivetrain and cause damage when the tires stick to a normal road surface. A full-time transfer case adds a computer-controlled differential between the front and rear driveshafts, allowing the front and rear wheels to rotate at different speeds. It works the same way as a rear axle differential, which enables the left and right rear wheels to rotate at different speeds while making a turn. The full-time transfer case offers the convenience and added traction of an all-wheel-drive system along with 4WD high and low lock selections for getting down and dirty.
Troubleshooting Electronics
Q: My 2003 Durango's front and rear windshield wipers and the power windows stopped working. Everything else works, including the radio, lights, heater, A/C, turn signals, etc. I checked the fuses and they're all good. A friend suggested it could be the ignition switch.
A: The ignition switch is a good guess, but you have to go through the motions first. Looking at the schematic, I see a common power supply to both circuits. It all starts at the Power Distribution Center, a black box with a cover located under the hood on the left side, near the master cylinder. If you remove the cover you'll find fuse #17. It's a big 50amp fuse. Hopefully, you have a 12volt test light handy. Connect the clip end of the test light to a good ground (anything metal bolted to the engine or chassis) and touch the pointy end to either side of the fuse. If it lights up on both sides, the fuse is good. If it only lights on one side, the fuse is bad. If it doesn't light at all, either you didn't ground the test light well or there's a break in a major circuit coming from the battery. Fuse #17 feeds power to the ignition switch. When the ignition switch is turned to the run or accessory position, power is sent to fuse #5 (20amp) to help power the wipers, and circuit breaker #28 (25amp) to run the power windows. You'll find this fuse and that circuit breaker in the fuse block on the left side of the instrument panel. It's facing the driver's door and has an access panel. Do the same procedure with the test light on the breaker and the fuse while the ignition switch is in the run position. If both have no power at all, it's a good chance the problem is the ignition switch. But you really have to access the switch at the base of the steering column to confirm the power coming in from the fuse under the hood, but not going out to the wipers and windows. It could be a poor connection somewhere in between.

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