F-250 Improper Downshifts

Question:  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?

Answer: 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.


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