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- Aug 5, 2024
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- Location
- California and Texas
- Vehicle Year
- 2002
- Make / Model
- Ford Ranger
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- Automatic
- 2WD / 4WD
- 2WD
tl;dr: Cranking and not starting then finally catching and running insanely rough for a couple of minutes then suddenly smoothing out may well be a coolant temperature sensor (CTS) issue: open circuit or high resistance if the problem is when the engine is hot; low resistance (not sure about a short) when the engine is cold. Differentiating between “sensor” (for the computer) and “sender” (for the dash gauge) by verbiage or details of physical shape may be insufficient to ensure the correct part is obtained. Best bet is to measure the resistance of the device.
Thanks to all the great information on The Ranger Station, i’ve searched and read and already benefitted significantly. Should have posted this (my first post on this site) a year ago, though the delay allows me to confirm that the fix is solid and reliable.
Brief background: my new (as of 2022) Love’s 2002 Ford Ranger with the 3.0L engine, AT, 2WD was poorly maintained and treated by a previous owner and some of her family members over its 233,xxx miles of running. All kinds of problems and all sorts of work done, with more to come.
Hot start problem
Amongst this vehicle’s many issues, a prominent one was being difficult to start when the engine was hot. Family lore was that sometimes the driver had to sit and wait for about 20 min. to let things cool down then try again. One cool December night, even that was insufficient: the truck stranded us 20-some miles from home. Hours of work changing the fuel filter, checking the inertia switch, patching vacuum leaks, etc. did not help. Had to be towed home.
Months of repairing vacuum hoses/lines, performing neglected general maintenance, cleaning electrical connections and more ensued, including a new battery. During the electrical connection cleaning, i discovered that the previous owner thought that it was OK to use epoxy to reattach the electrical connector end of the CTS to its body and that somehow magically the electrical connection continuity would be restored. Well, it wasn’t, which explains OBD-II P0118 Engine Coolant Temperature Sensor Circuit High Input having been set. The open circuit told the control module that the engine was stone cold, hence it started fine when it actually was cold, but not when hot.
Specific failure, for both the hot start and cold start (below) problems:
Cranks and cranks and cranks, but no catch, as though there’s no fuel or spark. After ongoing cranking the engine barely catches and runs super rough: rattling, shaking, almost like the timing was off, at below-standard-idle RPMs (≤200 RPM). Rough enough that i was concerned about engine damage from running that rough. Often it would stall out and die, and often we had to work around that via fluttering the accelerator to keep the engine going. After several minutes of this, all of a sudden the engine would jump to about 1,200 and smooth out then down to the typical 800 RPM for this vehicle.
In hindsight, fairly obvious why letting the engine cool would get it close enough to cold that it could again start. I’m not sure i was even looking at OBD-II codes at that point, given how many very obvious problems (e.g. missing vacuum hoses and the famous 90° elbow with the hole) needed addressing.
Ordered a replacement CTS from Rock Auto and put it in. And then…
Cold start problem
Suddenly the issue wasn’t hot starts, but cold starts. Corresponded with installation of the new sensor, but why? Yes, there was a P0117 code: Engine Coolant Temperature (ECT) Sensor Circuit Low Input.
It took studying live OBD-II data and noticing the following:
Engine coolant temperature 149.0°C
Very far above boiling! The CTS was telling the computer that the engine was on fire, so of course hot starts were no problem, but cold starts were not happening.
Further research made clear that for reasons i cannot fathom, Ford decided it was OK to have two different parts with exactly the same threads and electrical connectors fairly near each other on this engine, with very different resistance with temperature curves. Some sources insist that the sensor is the one connected to the computer and the sender is the one connected to the gauge, and that each device has specific physical details. I found that Rock Auto jumbled them all together on one page, and at least on that site there was no clear distinction between appearance and usage of “sender” vs. “sensor” in the accompanying text.
To ensure you have the correct part, measure its resistance:
At 23°C (74°F) ambient temperature i measured:
332Ω for the sender, connected to the dash gauge (two samples)
28.7kΩ for the sensor, connected to the computer (one sample)
The WVE 1T1117 from Rock Auto measured the same 332Ω as the existing older (likely factory) sender. I went to a local auto parts store with my DMM and got a CarQuest WTC1004, which as stated measured 28.7kΩ. A tolerance of ±10% seems reasonable, so approximately 25kΩ to 32kΩ at 23°C, or lower if the ambient temperature is hotter, or higher if it’s cooler should be all good. What’s not good is an order of magnitude lower, such as when a sender is installed in place of a sensor.
The truck still has issues, but starting isn‘t one of them. Since installing the correct sensor in spring 2023, it starts immediately and smoothly (as smooth as this tired engine runs, anyway) whether hot, cold, or anywhere in between—just like it’s supposed to.
****
This topic has been covered in the topic Need help with wiring for ECU temp sensor, and this message in the topic 2001 Ranger 3.0v6 is hard starting mostly when cold. Somehow i did not see those over a year ago when searching, and neither mentions specific resistance values for both sensor and sender, which i found very difficult to find online. This issue gave several people so many problems for so long, i thought it would be worth trying to give back to the community by making this much more specific post on this one possible failure mode that can cause this particular flavor of hard starting.
Thanks to all the great information on The Ranger Station, i’ve searched and read and already benefitted significantly. Should have posted this (my first post on this site) a year ago, though the delay allows me to confirm that the fix is solid and reliable.
Brief background: my new (as of 2022) Love’s 2002 Ford Ranger with the 3.0L engine, AT, 2WD was poorly maintained and treated by a previous owner and some of her family members over its 233,xxx miles of running. All kinds of problems and all sorts of work done, with more to come.
Hot start problem
Amongst this vehicle’s many issues, a prominent one was being difficult to start when the engine was hot. Family lore was that sometimes the driver had to sit and wait for about 20 min. to let things cool down then try again. One cool December night, even that was insufficient: the truck stranded us 20-some miles from home. Hours of work changing the fuel filter, checking the inertia switch, patching vacuum leaks, etc. did not help. Had to be towed home.
Months of repairing vacuum hoses/lines, performing neglected general maintenance, cleaning electrical connections and more ensued, including a new battery. During the electrical connection cleaning, i discovered that the previous owner thought that it was OK to use epoxy to reattach the electrical connector end of the CTS to its body and that somehow magically the electrical connection continuity would be restored. Well, it wasn’t, which explains OBD-II P0118 Engine Coolant Temperature Sensor Circuit High Input having been set. The open circuit told the control module that the engine was stone cold, hence it started fine when it actually was cold, but not when hot.
Specific failure, for both the hot start and cold start (below) problems:
Cranks and cranks and cranks, but no catch, as though there’s no fuel or spark. After ongoing cranking the engine barely catches and runs super rough: rattling, shaking, almost like the timing was off, at below-standard-idle RPMs (≤200 RPM). Rough enough that i was concerned about engine damage from running that rough. Often it would stall out and die, and often we had to work around that via fluttering the accelerator to keep the engine going. After several minutes of this, all of a sudden the engine would jump to about 1,200 and smooth out then down to the typical 800 RPM for this vehicle.
In hindsight, fairly obvious why letting the engine cool would get it close enough to cold that it could again start. I’m not sure i was even looking at OBD-II codes at that point, given how many very obvious problems (e.g. missing vacuum hoses and the famous 90° elbow with the hole) needed addressing.
Ordered a replacement CTS from Rock Auto and put it in. And then…
Cold start problem
Suddenly the issue wasn’t hot starts, but cold starts. Corresponded with installation of the new sensor, but why? Yes, there was a P0117 code: Engine Coolant Temperature (ECT) Sensor Circuit Low Input.
It took studying live OBD-II data and noticing the following:
Engine coolant temperature 149.0°C
Very far above boiling! The CTS was telling the computer that the engine was on fire, so of course hot starts were no problem, but cold starts were not happening.
Further research made clear that for reasons i cannot fathom, Ford decided it was OK to have two different parts with exactly the same threads and electrical connectors fairly near each other on this engine, with very different resistance with temperature curves. Some sources insist that the sensor is the one connected to the computer and the sender is the one connected to the gauge, and that each device has specific physical details. I found that Rock Auto jumbled them all together on one page, and at least on that site there was no clear distinction between appearance and usage of “sender” vs. “sensor” in the accompanying text.
To ensure you have the correct part, measure its resistance:
At 23°C (74°F) ambient temperature i measured:
332Ω for the sender, connected to the dash gauge (two samples)
28.7kΩ for the sensor, connected to the computer (one sample)
The WVE 1T1117 from Rock Auto measured the same 332Ω as the existing older (likely factory) sender. I went to a local auto parts store with my DMM and got a CarQuest WTC1004, which as stated measured 28.7kΩ. A tolerance of ±10% seems reasonable, so approximately 25kΩ to 32kΩ at 23°C, or lower if the ambient temperature is hotter, or higher if it’s cooler should be all good. What’s not good is an order of magnitude lower, such as when a sender is installed in place of a sensor.
The truck still has issues, but starting isn‘t one of them. Since installing the correct sensor in spring 2023, it starts immediately and smoothly (as smooth as this tired engine runs, anyway) whether hot, cold, or anywhere in between—just like it’s supposed to.
****
This topic has been covered in the topic Need help with wiring for ECU temp sensor, and this message in the topic 2001 Ranger 3.0v6 is hard starting mostly when cold. Somehow i did not see those over a year ago when searching, and neither mentions specific resistance values for both sensor and sender, which i found very difficult to find online. This issue gave several people so many problems for so long, i thought it would be worth trying to give back to the community by making this much more specific post on this one possible failure mode that can cause this particular flavor of hard starting.
