Low RPM at Highway Speeds and Accelerator Pedal Fully Depressed
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Professional
Joined: Aug 2022
Posts: 212
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From: CA
TLDR: Somehow, after replacing the o2 sensors, not only are the codes gone, but now my issue of no acceleration at WOT and highway speeds is solved.
I received my warranty o2 sensors and tested the existing o2 sensors (heater resistance, 1/1 and 1/2 were both at 4.5 ohms) and the wires at the harness from the PCM (voltage, with key set to on, ignition off, on 1/1 was 4.23 and 4.34 on 1/2, both had continuity to ground on the ground wire and no continuity to ground, or the other wires in the bundle). To my knowledge the resistance on the existing o2 sensors is too low, but the new sensors tested at 4.3 ohms. I decided to just pop them in since the existing ones were already unplugged and for all I know, potentially fouled from 200 miles of poor running on an unknowingly crappy aftermarket MAP sensor. The existing ones looked almost brand new but I still decided to swap them just to see. When removing 1/1, it seemed as if the sensor was quite loose as it only required one hard yank to loosen whereas 1/2 was much more difficult. The tranny shop I took it to seemingly remove the o2 sensors (and maybe the cats?) when they put the tranny in as there is colored paint on the connectors and the sensors that correlate to one another. After firing her up with the new sensors the codes didn't reappear, and the left bank successfully went to closed loop but the right bank failed to ever do so, at idle, roadway, and highway speeds. My guess is either the old sensors were somehow in fact bunk, or, 1/1 was too loose and there was perhaps a small exhaust leak from that location? Currently the transmission seems to having some delayed shifts, especially when significant throttle is applied, and the governor pressure PSI is still below target so the shop has some more work to do. Otherwise the engine runs like a charm.. I guess?
Huge thank you to everyone who helped me out on this multi-month gremlin hunt; if you're reading this in the future, the advice from me would be "ALWAYS buy OEM sensors for these trucks." I somehow passed smog, didn't throw any odd codes or obvious askew data, yet replacing an aftermarket sensor with an OEM product revealed three codes that, when rectified, completely solved my engine issues and finally made this truck safe to drive on the highway. Now to build the camper
I received my warranty o2 sensors and tested the existing o2 sensors (heater resistance, 1/1 and 1/2 were both at 4.5 ohms) and the wires at the harness from the PCM (voltage, with key set to on, ignition off, on 1/1 was 4.23 and 4.34 on 1/2, both had continuity to ground on the ground wire and no continuity to ground, or the other wires in the bundle). To my knowledge the resistance on the existing o2 sensors is too low, but the new sensors tested at 4.3 ohms. I decided to just pop them in since the existing ones were already unplugged and for all I know, potentially fouled from 200 miles of poor running on an unknowingly crappy aftermarket MAP sensor. The existing ones looked almost brand new but I still decided to swap them just to see. When removing 1/1, it seemed as if the sensor was quite loose as it only required one hard yank to loosen whereas 1/2 was much more difficult. The tranny shop I took it to seemingly remove the o2 sensors (and maybe the cats?) when they put the tranny in as there is colored paint on the connectors and the sensors that correlate to one another. After firing her up with the new sensors the codes didn't reappear, and the left bank successfully went to closed loop but the right bank failed to ever do so, at idle, roadway, and highway speeds. My guess is either the old sensors were somehow in fact bunk, or, 1/1 was too loose and there was perhaps a small exhaust leak from that location? Currently the transmission seems to having some delayed shifts, especially when significant throttle is applied, and the governor pressure PSI is still below target so the shop has some more work to do. Otherwise the engine runs like a charm.. I guess?
Huge thank you to everyone who helped me out on this multi-month gremlin hunt; if you're reading this in the future, the advice from me would be "ALWAYS buy OEM sensors for these trucks." I somehow passed smog, didn't throw any odd codes or obvious askew data, yet replacing an aftermarket sensor with an OEM product revealed three codes that, when rectified, completely solved my engine issues and finally made this truck safe to drive on the highway. Now to build the camper