I have a '99 F150 4.6. I want to change the engine coolant temperature sensor because I'm getting poor gas mileage. I looked at the Chilton's manual and it shows it on the engine block behind the altenator but I looked at my engine and I can't find it. Has anyone else changed this sensor? Where is it located? Any help is appreciated.

 

How do you know that it is the ECT sensor causing your malady?

 

Actually I don't know for sure the ECT sensor is faulty, but I've tested or replaced almost everything else I can think of. The spark plugs might be likely culprit but they are only have 30-40k miles on them and are a pain to change. Since my truck seems to run fine and the ECT has alot to do with the fuel mixture and it only costs $20, I thought I'd try changing it and see if I get any improvement.

 

Actually I don't know for sure the ECT sensor is faulty, but I've tested or replaced almost everything else I can think of. The spark plugs might be likely culprit but they are only have 30-40k miles on them and are a pain to change. Since my truck seems to run fine and the ECT has alot to do with the fuel mixture and it only costs $20, I thought I'd try changing it and see if I get any improvement.

 

Your flying around in the dark! What do you consider poor fuel mileage on a relitive basis.
We have yet to hear about some number you consider unacceptable.
The ECT does indeed have an effect as does the IAT, Ox sensors and other items, driving habits, tire pressure and even gas quality.

 

I have a 99 f150 4.6 also. Gas ain't cheap. Try dumping a can bg 44k in the tank at the next fill up. It's about 20 bucks. Cleans all fuel system components it flows thru including injectors.

 

Most of the V8 F150's dont use ect sensor they use the cylender head temp sensor which is on the drivers side head under the intake manifold it can be reached by removing the alternator and accessing it from the opening. I think that you will be wasting youre time changing it unless you are throwing a code. A new 192 thermastat may be of more help than the sensor. the best things to improve gas milage are front oxygen sensors good air and fuel filters proper tires size and air pressure, no aerodynamic loosing accessories, mud flaps, visors, bug shields etc each one can cause a loss of 1 MPG You will never see high mailage as these trucks are very heavy but I can get 18.4 highway and 15 local with my 4.6 2wd supercrew and thats driving at normal + highway speeds in Western PA a lot of ups and downs. The biggest differance I saw was changing front O2 sensors, in both performance and fuel milage.

 

I appreciate all the input. I used to get 18-19 mpg, after all the mods. I drive the same distance to/from work everyday and noticed a sudden drop in mileage, like 14-15. I have done everything already suggested and more. I changed both front 02 sensors, filled tires to max pressure, new fuel filter, sea foamed it twice through brake booster, put in a new EGT, removed and cleaned throttle body (EGR ports were totally clogged), changed IAT, put in fuel injector cleaner, new air filter, new MAF (it threw a code) and probably a few more things I can't remember. I noticed a good improvement after changing the 02's, after installing EGR and after cleaning the TB. Each time though the mpg improvement only lasted a few days until the computer could learn to make the air/fuel mix rich again (I'm guessing here) and therefore consume more fuel. I'm running out of ideas and with gas prices so high it's killing me! I know something is wrong, it uses alot of gas just going across town. Will a scan tool like an Actron tell me if I'm running too rich?

 

I have never gotten over 15 mpg, bone stock or with my mods - 14.7 tops.
I drive city streets 90% - I'm original owner - never a code - good maintenance, etc.
The more you mod, the heavier your right foot gets anyhow.

 

Check your fuel psi, should be around 30 to 40 psi. Low fuel psi can lead to lean conditions.


I am fighting mine now as I had a code P0118 (second one in 3 months)
As you said above this could be a problem regarding a lean condition.
I replaced it this morning and now I am getting a P0305. Enigne backfires through intake ect ect lots of Pinging. Trying to find a coil to use as a test subject. I checked the plugs/wires ect. All seem to be in excellent condition.

However upon a test drive with a fuel psi gage taped to the window I have found my max fuel psi is 30 psi and idles at 20 psi. Considerable drop from a 30 at idle and a max of 60. So best I can figure I need a fuel pump with filter replacement and a coil pack.

I only get 13.5 mpg but I have larger tires and a body lift so I am not expecting VW style results

Good luck.

ps... BTW
The sensor you seek is on the right side (Passanger side) right behind the alt. cable bracket. I removed the throttle linkage just to make it easy to replace.
The part number for the sensor from Napa is "TS4047"

The other sensor you see just in front of it is the gauge sensor for your cluster pak.

Again Good luck.

 

Very good point about fuel pressure too high or too low will make the computer compensate and affect the milage. After replacing parts have you dissconected battery for a while to let the computer loose it's memory and all it's bad habbits? Also the delta pfe sensor that controls the egr flow can do a lot of crazy things to the computer and many times if not completly failed will not set a code.

 

To emonster,
With fuel pressure varying that much you have no fuel regulation.
The pump pressure does not vary with engine speed unless there is a very bad problem with the alternator output varying the voltage to the truckand the pump.
You need a regulator.

 

It sounds like a good idea to check the fuel pressure. I did test the dpfe sensor following instructions from another post, it seems fine. I believe Chucks BP is correct that I have the cylinder head sensor. The chiltons manual shows the ECT exactly as emonster described but mine's not there. It looks like its underneath the manifold, behind the alternator like Chucks said.

 

how many miles on the engine? when was the last time you swapped out the plugs? Or wires (as a last resort, lots of ching and labor intensive). Weak spark in one or more cylinders could create a rich condition and affect new o2 sensors. If you have mandatory emissions where you're at, compare the last check when you were getting 18mpg to a new one. Any good shop can do it.

 

@ BlueGrass,

My Fuel PSI is about 10psi different from idle to road speed (app 60 to 65 mph)

I idle at 20 to 22 psi and at speed I am 28 to 30 psi Steady app a 10 psi difference.

Am I wrong to assume the regulator is good ? Now I am confused, I thought I had a pump going south on me not a regulator.

Can some one give me real world fuel psiI readings ?
Example,
@ Idle
@ Road speed

I dont have a mini vac handy so I cant check max amount, I can only do road test.

1997, F150 4x4 4.6l

Also sorry didnt mean to hi jack the thread.