Shift Pointers: A 10R140 with a classic drivability complaint - Transmission Digest

Shift Pointers: A 10R140 with a classic drivability complaint

A 2021 F-350 6.7L Super Duty using the 10R140 beast of a transmission recently came into Precision Auto Repair not upshifting when pulling a load only. On light throttle it would upshift, but not as high as tenth gear. Once the throttle was depressed it would downshift and no longer upshift. It displayed similar symptoms to when the wrong tire size is used with vehicles that have highly sensitive curve recognition programs. In these applications (such as a BMW), when wheel speed signals indicate the vehicle is in a turn, it will prevent any shifting. If tire sizes are wrong, it can deceive the computer’s logic system in this way preventing an upshift with medium to heavy throttle. But that is not the case here. This is a 10R140 with a classic drivability complaint.

When Jarrell at Precision Auto Repair received this vehicle, the first thing he did was pull codes. It had only one, P1548 for an Engine Air Filter Restriction. He cleared the code, yet the problem persisted. He decided to inspect the filter and sure enough, it was loaded (see Figure 1).

Figure 1.
Figure 1.

There is a restriction gauge located on the upper housing of the air filter assembly. This device measures the vacuum inside the air filter. The more the air filter is dirty or clogged, the higher the vacuum reading. When the airflow in the intake air system reaches the maximum allowable restriction limit, the air filter restriction gauge indicator moves from the yellow bar to the red bar at the base of the gauge (Figure 2).

Figure 2.
Figure 2.

There have been reports that sometime in 2022, Ford eliminated the use of this gauge, so you may not find it; but if you do, it will need to be reset after the cause of the restriction is resolved. If you are an owner of a Ford Super Duty with this gauge, it is recommended that it be checked every 7,500 miles. If the truck is being used in extremely dusty conditions, this should be checked every 500 miles or two weeks—whichever comes first. The air filter will need to be changed when the restriction gauge reads near the change filter line and the gauge is yellow. Once it is in the red, the engine is suffocating, and classic drivability complaints will be present, affecting fuel economy as well.

Read more columns from our Shift Pointers series here. 

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