When cruising at 60-65 mph on the highway and hitting a steep incline, I press the accelerator to try to maintain or increase speed, but the RPMs stay locked. For about 5 to 10 seconds, the truck doesn’t respond to the additional pressure on the pedal. During this time, I notice the fuel pressure drops slightly from the usual 60-62 psi to around 55-57 psi, and the EGTs rise, but there’s no increase in RPMs.
If I press the pedal down much faster and further (almost WOT), the RPMs spike, the engine roars, but the speed either barely increases or stays the same going up the incline. It seems like the transmission is not downshifting correctly, and I suspect the torque converter might be the issue. I found a video online where someone else suspected a faulty torque converter causing a similar lockup.
What I usually do is ease off the accelerator to force the transmission to downshift, then press the pedal again to gain speed.
This is a new 4R100 transmission with no more than 10k miles on it. Transmission temperatures stay below 180°F, even when towing heavy loads up steep Colorado inclines on a hot day.
Could the issue be related to the exhaust back pressure valve? It sounds similar to what mine would do on cold days. If you let off the pedal and then press it again, do you get a response?
Someone else mentioned that recently. I need to test it with FORScan to confirm if it’s a real issue. I usually hear when the valve is closed or mostly closed, and I haven’t noticed anything unusual in that regard.
Have you tried turning off overdrive before tackling the steep incline to disengage the torque converter lockup? This will cause it to downshift into third gear, providing the power you need. Trying to maintain speed in overdrive on a steep grade can quickly damage a 4R100, regardless of any modifications.
Your exhaust gas temperatures rise because the truck is adding more fuel as you press the throttle.
The lack of acceleration might be typical of a stock 7.3, which often struggles to accelerate at highway speeds in its stock form. Consider trying a Hydra with a mid-power tune; it should improve throttle response significantly.
You can engage overdrive off on the fly in many vehicles, including while driving up a steep incline. It’s typically done by pressing a button or flipping a switch, but you should check your vehicle’s manual to confirm how it’s done for your specific model.
It’s good to hear that the Hydra tuner and the KC balanced assembly have improved your throttle response. Given your concerns about potential damage to the 4R100 transmission, it might be worth having it inspected by a professional. They can check for any signs of wear or stress that might have resulted from running with overdrive engaged on steep inclines.