It has been my understanding based upon much research that the 99-03' 7.3l diesel MANUAL TRANSMISSION engines typically only have one ECT (engine-coolant-temperature) sensor. This sensor is located on the waterpump/thermostat-housing. It is threaded down into the engine from the top.

That is to say; the sensor is on a vertical axis. Just like this --> |

I have found rumors of a SECOND ECT sensor only found on SOME 7.3l MANUAL TRANSMISSION diesels.

The second ECT sensor is very difficult to find, somewhere in the vicinity of the passenger side head, up near the belt tensioner -- some have gone as far to say that the sensor can only be "found" by feel. Very difficult to locate, and almost impossible to get a clear picture of.

I have been trying to diagnose a low-power condition on my 7.3l, and I have located two chaffed wires which the previous owner thought smart to wire-nut together.

Based on my understanding -- an ECT sensor is a thermistor sensor. It works on variable resistance. If the resistance through sensor is LOW, the PCM/ECU believes that the engine is HOT. If the resistance is HIGH, the PCM/ECU believes that the engine is COLD.

Now let's read this.

And finally -- this, as posted on another forum.

I am trying very hard not to make assumptions.

However, the two wires which the previous owner has wire-nutted together correspond to the wire colors of this fabled "second" ECT sensor.

If the two wires are nutted together -- instead of being connected to an actual functioning ECT sensor, the PCM/ECU would receive a "low-resistance" reading from this secondary ECT sensor, therefore believing that engine is above 225*F and overheating. If my assumption is correct, let's again read this...

Has anyone followed my logic this far? If so, what do you think?

This truck is SLOW. I was towing 7tons up a very steep hill the other day, and second gear would not do it. By second gear I mean (2) on the stick shift. I charged the hill in second gear and halfway up the hill I had to rev the engine RPM very high and burn the clutch as I downshifted into (1) 1st gear so I could make it to the top.

I'm new to diesel engines, but I'd expect more power out of 7.3 liters of engine displacement.

Anyone? Thank you for your help.

 

Do you have a way of monitoring EOT=Engine Oil Temperature? That would be more definitive as a way of determining the temperature of the engine.

 

One who knows for sure should soon chime in. I have heard several times that the AE scanning tool reads water temp ONLY on a truck with a manual transmission. With the automatics it give an erroneous number for water temp. I do not know where it senses that water temp.

 

Trucks with manual tranny's have 2 sensors. One goes to the dash gauge, the other feeds to the PCM.

Trucks with autos only have one sensor that goes straight to the dash gauge. Automatic trucks do not have an input to the PCM for the coolant temp.

Any attempt to read coolant temp from a scan tool on an automatic equipped truck only results in erroneous readings.

To accurately diagnose a biased sensor on a manual transmission truck, you need to hook up a scanner and get readings. Start with a truck that has completely cooled off to get a baseline. Your ECT and EOT (Engine Oil Temp) should be very close to each other, and close to ambient temps if the truck has sat overnight. If you find one or the other wildly skewed, then you are on the right path to diagnosing the problem. You can then run the truck until it's fully warmed up and check the readings again.

 

This might help. Ohm the sensor and see if unplugging the mystery wires will register on the meter. If so, follow them to the sensor.

 

Okay, simple question. WHERE is this secondary ECT sensor located?

We all know about the one on the waterpump/thermostat housing.

Now for the second sensor...... where is it?

I have no sensor in TorquePro that pertains to engine coolant temp.

One sensor is listed as "ECT - From TCM" ------------ but that sounds like "traction control module" and the value is constantly at -40*C

It seems very strange that I cannot get a sensor to display coolant temperature in torquePro.

 

1 sensor is on drivers side below thermo housing, other sensor is on top of water pump. Depending on year of truck will determine which pin corresponds to coolant temp for pcm. Mine ended up being tft trans fluid temp because I swapped a manual in. If it is an 02+ you may have a check engine and check gauge on depending on which sensor pig tail is used. You can get the pigtail from ford and add the sensor if you want

 

I have one sensor in the top of the water pump.

On the side of the water pump, below the thermostat housing -- on the driver side -- there is a brass plug threaded into the water pump. It was there when I bought the water pump and installed it.

Is that where my second coolant temperature sensor should be? There is no sensor, just a brass plug in the hole.

Are you saying that I can get the wire pigtail to connect to the two loose wires under my hood and install a sensor there?

 

That is correct, or at least what I did. My truck was an auto but it has all the wiring to emulate a manual. You will need the pigtail. Before tearing things up, i would disconnect the connector at the computer and continuity test the two wires to see where they pin out to so you don't send an incorrect signal by hooking them up. One is Vref that is shared between other sensor Vref supply signals (about 5V). The other wire is your return signal which sends less than 5V back since it is a thermal resistor sensor (simple ohms law). You could always check voltage on the two wires to see which is Vref as well.

 

My picture was the engine side of the 42-pin connector over the driver-side valve cover. It takes a 10 mm socket to spin the connector bolt out (the bolt is not loose, it will not fall out). Once the plug is off, you will see the part in the picture. I looked at every Superduty wiring diagram for the 7.3L, and the ECT was pin 18 for every year of that combination vehicle/engine. This is much quicker and easier than pulling the PCM and decoding the pins there.

 

Fixed it or ya.

My google-fu is strong today so I plucked the pic below from the ether. I'm thinking location B10 matches your description. If feeling around is inconclusive, snake your cell phone down there and take a video, maybe find it that way. Doubt you'll get a straight look at it. Since one description specifies "engine" and the other does not I'd assume that B10 goes to the PCM and B214 to the dash. Plus B214 is the typical AT location and those only go to the dash. Found the pic HERE.

 

what david posted. Hoping my google-fu is strong this morning , because there IS a pic from a member(other forum) that posted a pic of THIS SAID ect....give me a few.

EDIT...found it

http://www.powerstroke.org/forum/99-...-sensor-2.html

 

^^^^^ found it. edited my post

 

Corksil, I follow your logic, except for the thermistor. They can have either positive or negative coefficients, meaning resistance can rise with increasing temp (positive), or decrease with increasing temp (negative).

The second ECT sensor on our manual trucks feeds the same PCM input as the transmission temp sensor for auto trucks (pin 37 IIRC).

Some people have reported that they can get valid readings from AutoEnginuity, reading the PID for ECT. Other people cannot. I'm one of the people that gets a bad reading from AE. It could be the version of AE that I'm using, or it could be that I have an '02 truck.

Having the ECT sensor wires shorted together ain't good. I'm not sure if the PCM would assume a faulty sensor and use a default parameter, or if it would "defuel." The second ECT sensor is relatively cheap - the local Ford dealer had one for $15. Make sure the guy behind the counter specifically matches the part number to the one for manual transmission trucks - it's a different sensor than the one that feeds the dummy gauge in the dash.

Your issue could possibly be from this sensor, or could be from any number of other things. Has the truck run like this since you bought it? Those wires have been shorted ever since you bought it, so if this is a new decrease in performance, it's not from that sensor.

Is your oil fresh, and proper diesel oil? Clean air filter? Getting a scan tool of some sort and monitoring ICP, ICP DC, FIPW, and RPM while driving would be the first test. Also, check the MAP (psi), EBP (psi), and BARO (psi if you can, volts if not). Those three readings should all be within .1 or .2 psi of each other. If one of those is screwy, your fueling would be affected.

 

I tested my spare ECT sensor. It is negative coefficient, meaning resistance decreases as temp increases. A short (wire nut) would equate to a very high temp. But, the PCM may have a check in place for that sensor, and may be using some kind of default program if it hasn't seen a change in ECT readings. I know that the PCM has a check for the EOT sensor, and will assume an oil temp for startup, and an oil temp for running, if "bad" readings are coming from the EOT. I'm not sure if it does the same for ECT.