How will the engine NORMALLY act when an ECT goes bad?

 

well first of all what year and what motor? I have a 1991 ford f-150 with the inline six. I have a sensor for the temp gauge on the passenger side of the motor below the manfold on the side of motor. and on the top of the motor where the thermostat housing is there is another sensor for the water temperature that i do belive is for the motor. i dont know if this can help you.

 

You won't notice a thing, but it will suck gas like there's no tomorrow.

 

CrossF150 is correct (Actually, AndyM is too).

There are two sensors, one on or around the coolant neck on the block, and another on the side of the engine sticking in the crossover port.

The former is what the EEC and the cluster use to measure actual temperature. The one on the side of the intake tells the EEC that the thermostat opened - so it knows to try and go into closed loop.

If *either* is bad or dysfunctional, you're gas mileage will be horrible, just for different reasons

 

I thought the EEC used the two wire one exclusively (I know it did on the older stuff, not sure about OBD-II stuff)

 

The one on the coolant tree is the ECT (Engine Coolant Temperature) sensor and the one on the intake is the ACT (Air Charge Temperature) or IAT (Intake Air Temperature) Both are approximately the same resistance. The ECT serves to notify the ECM when coolant temperature is high enough to switch to closed loop and monitor the O2 sensors for controlling fuel mix. The ACT or IAT is to monitor intake air temperature. While not as accurate as Mass Air Flow measuring, colder air is denser, warmer air less dense. This signal is pretty much ignored until the engine is up to temp as well. When cold, the ECM pretty much ignores all the sensors, and just runs from pre-programmed fuel models in the EEPROM, based on RPM and Throttle position. After up to operating temperature, then it figures out what the mix should be based on MAP (Manifold Air Pressure), Engine Coolant Temperature, Air Charge Temperature, and Oxygen content in the exhaust.

The single wire sending unit in the intake manifold water jacket is for the idiot light or gauge (if equipped). I'm not real sure if the sending unit varies, because on my old T-Bird, the light is controlled by the ECM. But, grounding the single wire will make the light come on, and has NO effect on the operation of the engine, open wire, or shorted to ground. This dates back to the earliest gauges, and I guess Ford decided to keep it separate from the actual sensors for engine management. My guesses are that the ACT is much more sensitive and accurate than the single wire sending unit.

Hope this helps.

 

The reason for the two wire sensors is to isolate noise and keep it out of the sensor circuit. The second wire is a dedicated ground used only by the computer sensors which keeps noise from other electrical devices from altering the signal. The computer doesn't really ignore the sensors on cold start up, rather based on the temperature value they are reading, the computer goes into cold start mode, where fuel is trimmed rich based on air temp and engine temp. The percent trim gradually decreases as the engine and air temp increase. The computer uses MAP to figure engine load whether the engine is cold or hot or anywhere in between, although at full throttle, the computer is programmed for certain fueling based on rpm only (though still trimmed by temperatures).

 

Interesting. My 93 F350 has two multi-wire coolant temp sensors, one in the neck and one on the side of the intake. If I remove either of them, a check engine light comes on, and if I remove the connector to the one in the neck, the gauge doesn't work any longer and the EEC has no clue of temperature.

I'm pretty sure my crewcab isn't unique.

 

That's the first I've heard of that to be honest. Everything I've seen has one two-wire sensor and the single wire sender for the gauge.

 

You sure this isn't one of your modifications?

None of my trucks are like that, either. One sender has a one wire connector that only goes to the gauge. The EEC doesn't know or care a thing about it. The other is the ECT that goes to the EEC.

 

Nope, what I quoted was there when I started integrating the t-bird digital cluster, and I traced all the wiring. On my truck, both temp sensors can be swapped in location and wiring, no problem - connectors are identical.

See, the EEC provides a 5v reference voltage to both sensors on my truck, which was a problem because the t-bird cluster does the same. So what I ended up doing was adding a third sensor in the upper radiator hose with an adapter I made to splice the cut I made.

 

If the engine was warm it may not start is the most common problem that you hear about.
The ETC sensor is the most important sensor you have.

The ETC sensor has two wires on it and goes to the EEC only. It has nothing to do with the Temperature Gauge.

It is one of only two sensors used during Start and Crank, the other is the RPM.

It is the main sensor used for fuel management during the full range of operating temperatures.

What problem are you having with your 88?

For more information go to:


http://fordfuelinjection.com/?p=2

 

I just looked at 1993 T-Bird with Electronic Cluster and it also uses just a one-wire sender.

 

ECT may be used to set a target a/f ratio, but it is hardley the main sensor used to determine fueling requirements for the engine.

 

You might be thinking about the HEGO sensor but the EEC does not even look at it until Warm Idle. The TPS is not looked at until Cold Drive-Away.
If it is not the ECT sensor what do think is your main sensor.
If just about all of the rest of the sensors go bad the EEC will use the last known value and run with that but it can not guess what the ECT is suppose to be and you will not get an error code if it is bad.
Most of the time you can not even start the engine if it is bad and you do not get any codes, just 111 or 11.