Sorry my error, it is a two wire sensor on this one but the other wire just goes to ground.

 

I drove my truck around for a week with the ECT broken completely off. Never had an issue starting it or driving it. I did get absolutely horrible gas mileage, though. I didn't check the codes, I kinda knew it was bad.

I always thought the ECT was there primarily to tell the PCM when to go into closed loop.

From that point on, it relies on the HEGO, the TPS, and the MAP sensor, to a lesser degree, to determine how much fuel to inject - doesn't it?

Somebody edumacate me if I'm wrong.

 

That's the way I recall the E/F-series speed density working.

 

If the ECT is broken completely off you would have 0 Voltage and the EEC would think the engine is cold, it would start fine and would never look at or use the HEGO sensor. Your engine would always run in Open Loop.

I have helped about ten posters on here that there engines would not start while warm, they had to let it set for about 30 minutes to an hour to restart and in every time it turned out to be the ECT sensor was bad.

I guess if they unplugged the ECT sensor it would have started right up and ran with black smoke.

 

The MAP sensor is the driving force behind speed density fuel management. Speed Density remember? Speed is engine rpm, density is determined by MAP, manifold absolute pressure. The main fuel map/table is trimmed using multipliers for ECT and ACT. The ECT plays a bigger role in starting because engine temp has a lot to do with fuel requirements due to the temperature of the combustion chamber walls which makes the fuel more likely to condense, but the ECT is still not the main sensor the computer uses for fueling requirements. A colder engine takes more fuel, and takes gradually less and less as the engine warms. TPS is used for accel/decel enrich/enlean and is used at WOT to signal the computer to go into the RPM based fueling strategy for max power (open loop), and to signal closed throttle for overrun fuel cut and idle. The O2 sensor signal allows the computer to develop both short and long term trims based on the lean/rich signal.

 

Looking through the Sensors in use there are only two sensors that are used in every Strategy, they are the RPM and ECT. The only reason I said the ECT was the main sensor is that I normally do not think of the RPM sensor as being a sensor. So I guess the RPM is just as important as the ECT, but all the rest are somewhere down the line. The MAF or MAP and TPS sensor is not even used until Cold Drive-Away and the O2 is not used until Warm Idle and is not used in Full Throttle or Deceleration.
I would think that number three in importance behind the RPM and ETC would be the ACT Sensor and then the MAF or MAP and TPS.

 

The MAP sensor is the number one sensor. Every other sensor is just used to fine tune the injector pulse widths to supply the required/optimal amount of fuel. It isn't a Speed Temperature system, it is Speed Density. The computer starts using the O2 sensor feedback once the engine is warm for all operating conditions except WOT and decel, like you said. The O2 sensor is actually one of the last things, if not the last thing the computer uses to adjust the air fuel mixture. The O2 sensor can be used to correct small discrepancies between the aim AF mixture and the actual AF mixture, but does not play a large role in determining the amount of fuel to inject. If the engine was operated at the same conditions under which Ford did the calibration on the computer, it would operate spot on without any O2 sensor feedback.

If you are using fordfuelinjection.com for the strategy information, I recommend getting a second reference, because it isn't as accurate as some other sources I've found.

Engine temperature has nothing to do with engine load at all, so it would be impractical to use it as a main sensor for fuel requirements across the rpm and throttle (load) range.

Ford Fuel Injection and Electronic Engine Control by Charles D. Probst is an excellent reference for how these trucks (and other Ford vehicles) EFI systems work.

 

To EPNCSU2006

It sounds like we are talking about two different things, I am trying to get the engine started and running and you are talking about adjusting Fuel/Air Ratio after it has warmed up and running at speed.

Do not forget we are in grenas Thread and grena was asking about the ETC sensor and not all this other stuff.

Basically as you said above, the ETC has two wires and only goes to the EEC. The Temperature Sensor has one wire and only goes to the gauge.

I entered into this Thread to support you with where the wires go and not to get into an argument.

 

Right, I'm just saying that the ECT, while it plays a big role in cold start up, is not as important as you are claiming.

I wanted the correct information to get out there as well.

 

To SubFord:

To answer your question as to what problem I have with my 1988 Ford...

I have a surging idle.

It will start up and have the normal high idle of about 1100 and hold it for a few seconds. Then it will almost die (400-500 rpm), then shoot up to 1000-1100 rpm and repeat this cycle.

I was wondering if there was ANY chance that the ECT could have anything to do with this...

If not, what direction would you recommend that I go to address this?

 

I do not think the ETC would cause this.
You may have one of three things wrong.
1. Dirty or bad IAC.
2. Bad TPS.
3. EGR valve not closing.

One poster even said he fixed it by changing the plugs, plug wires, rotor, and cap.

 

Yes, very unlikely to be the ECT. If you haven't given it a tuneup, changed all the filters, and pulled the codes already, I would start there. It could also be just a dirty throttle body, which you can fix with a brush and some carb, throttle body, or brake parts cleaner.

 

Andym,

No codes.

Al the tune-up parts and filters are new. In fact, everything is new and clean other than the computor, wiring harness, vacuum harness etc.

 

Let me back track then, I do not see how but I have heard roomers that the ECT sensor can do this.

All so I have hear that Ford has some replacement part to fix this in older FI engines but have been unable to track this one down.

 

I think the Ford part that you are thinking of is what some people around here call the "Holy Grail."

It's more or less a way to adjust idle speed without raising the voltage @ the TPS.

It mounts between the IAC and the throttle body.

I have not tried one yet.

I have heard mixed success stories.

As for the ECT, I just unplugged it and plugged in a known good one and let it sit in the open air then started the motor. Nothing changed...