Stalling, Surging, Hesitation
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Senior Member
Joined: Jun 2020
Posts: 106
Likes: 6
Wow! Frustrating, but very interesting. Some "thinking out loud," for what it's worth, as I read through your posts:
- There are a couple clues that would give me some near term direction. She runs fine when the air temp sensor is unplugged, but neither the old nor new air temp sensor, when plugged in, runs as well. Thoughts: I believe that when the sensor is unplugged, the computer uses default values. So the values it's receiving with the sensors plugged in are likely extreme values that it tries to compensate for by adjusting idle with more or less fuel. Since neither the old nor new sensor fixed the issue, I would look at the sensor wiring to see that it isn't corroded with age and sending/receiving skewed signals. Time to break out the voltmeter.
- similarly, when you crank up, it runs fine until it gets warmed up, then starts to surge. At initial startup, the engine is in closed loop, and runs off of default values. Once warmed up, it takes inputs from the sensors and dynamically adjusts idle. Input from your sensors makes it surge, bog, etc., and in general use too much fuel. I would focus on the sensor inputs, beginning with the coolant temp sensor for which there was an error code. With that code, the computer thinks the coolant temperature is either very hot or very cold, and adjusts fuel accordingly. Check coolant temp sensor functionality and wiring integrity with voltmeter.
Other codes:
- I'm assuming you did your tests before replacing the components you list as having been changed out? It may be time to clear the codes and run another series of tests to make sure the replaced components are functioning properly, and addressed the codes.
- did you thoroughly clean the throttle body ?
I recently bought a 93 F150 5.0 with everything wrong with it except it would crank and idle, but that was with some "rigging" by the PO. Little by little, as I repaired/replaced sensor wires, and replaced sensors that did not function properly, she ran better and better.
- There are a couple clues that would give me some near term direction. She runs fine when the air temp sensor is unplugged, but neither the old nor new air temp sensor, when plugged in, runs as well. Thoughts: I believe that when the sensor is unplugged, the computer uses default values. So the values it's receiving with the sensors plugged in are likely extreme values that it tries to compensate for by adjusting idle with more or less fuel. Since neither the old nor new sensor fixed the issue, I would look at the sensor wiring to see that it isn't corroded with age and sending/receiving skewed signals. Time to break out the voltmeter.
- similarly, when you crank up, it runs fine until it gets warmed up, then starts to surge. At initial startup, the engine is in closed loop, and runs off of default values. Once warmed up, it takes inputs from the sensors and dynamically adjusts idle. Input from your sensors makes it surge, bog, etc., and in general use too much fuel. I would focus on the sensor inputs, beginning with the coolant temp sensor for which there was an error code. With that code, the computer thinks the coolant temperature is either very hot or very cold, and adjusts fuel accordingly. Check coolant temp sensor functionality and wiring integrity with voltmeter.
Other codes:
- I'm assuming you did your tests before replacing the components you list as having been changed out? It may be time to clear the codes and run another series of tests to make sure the replaced components are functioning properly, and addressed the codes.
- did you thoroughly clean the throttle body ?
I recently bought a 93 F150 5.0 with everything wrong with it except it would crank and idle, but that was with some "rigging" by the PO. Little by little, as I repaired/replaced sensor wires, and replaced sensors that did not function properly, she ran better and better.