Hello, I picked up my new old 96 Ranger tonight and while all the gauges move two of them are way off.

The temp gauge barely moves off C, the oil gauge stays in the middle (not rev dependent) and ODO is dead.

Are Ranger gauge issues common like mid-00's Chevy's or is it likely the senders? Thanks.

 

Oil pressure gauge is run by a Switch sender, above 5psi switch is ON, so needle goes to 1/3 to 1/2, set by a resistor inside the gauge
So no movement on pressure changes only voltage changes, pressure under 5psi would show 0 pressure on the gauge
Ford did this on all its vehicles back in the late 1980's
So an "idiot light" in gauge form

Temp gauge could be a bad Sender
1996 Ranger will be fuel injected so will have an ECT(engine coolant temp) sensor for the computer AND and ECT SENDER for the dash temp gauge
Sensor is 5volt
Sender is 12volt
so NOT interchangeable

Sender usually has 1 wire, sensor always has 2 wires, they look similar
Auto parts guys will ALWAYS give you a sensor first time around, so spell S E N D E R for them

Locate the Sender, unplug its wire, then use a jumper and GROUND that wire
Turn on the key
Temp gauge should go to HOT, if it does then wire and gauge are OK, replace sender
If it doesn't then its a wire or gauge issue

And it could be the thermostat is stuck open, so engine is NOT heating up, lol, so gauge is correct


1995 and up Rangers have an electric speedometer/odometer setup
The odometer worm gear was plastic and it could fail after 10-15 years or so
How-to on replacing it here: http://www.odometergears.com/documen...eplacement.pdf

 

Thanks again RonD... Good to know it's the normal oil pressure gauge behavior.

I felt the hoses as the engine idled before I took it home and the thermostat does seem to be working but it's on my list for replacement anyway. I got the OBD working again this afternoon and pulled one code p0125... which confirms my suspicions about the temp sensor(s).

I watched a video about the worm gear last night but I'm not going to worry about it (unless the fuel gauge is funky) since the vehicle is already "not actual mileage" and is odometer exempt anyway.

 

p0125 references the ECT SENSOR being too cold

P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control

So it is a thermostat issue most likely

There is no code for Senders, they are not connected to computer

ECT sensor needs to see upper engine coolant get above 180deg or so, and stay above that, or you will get that code

When engine is cooler, computer runs in OPEN Loop which is like Choke mode so poor MPG, computer allows about 8 minutes for engine to warm up.

If there is an ECT sensor problem then you would see
P0115 Engine Coolant Temperature Circuit Malfunction
P0116 Engine Coolant Temperature Circuit Range/Performance Problem

So P0125 means temp is really lower than it should be and dash gauge confirms that


After cold start put hand on upper rad hose, if its getting warmer then thermostat is stuck open
Upper hose should stay cold for at least 5 to 8 minutes as engine gets up to 190-195degF, thermostats rating, then it will heat up quickly as thermostat opens a bit

 

Update...

Live reader stated coolent temp was -27F (was actually 65F ambient)

Replaced both Temp sensor and Temp sender


Old temp sensor pins read 991KOhm (open)
Temp sensor power wire reads 4.65 Volts
Temp sensor ground wire reads 0.00 ohms
New Temp sensor pins read 37.1KOhm (correct)
Engine temperature now +337F (engine is cold)
Temp sensor unplugged is -40F

Why am I seeing 337F?

 

Reads like there is a short to ground, computer is seeing 0 ohms to ground so 0volts which is max temp

Data table here: https://www.freeautomechanic.com/images/ect3.gif

Yes the sensor should show about 38k at 65degF

Then sensor should drop to about 3k when coolant is at 190degF

Computer uses voltage, 5 volts out, if it gets back 3volts then computer knows engine is cold, 70degF, as voltage it gets back goes down it knows coolant is warming up, under 1 volt is warmed up

 

Chart doesn't make sense, my understanding of an ECT and thermocouples in general, is that the resistance gets lower as the temperature gets hotter. The computer should see more voltage passing through the sensor when the engine temperature gets higher. That corresponds with -40 being shown when the circuit is open and 337 being when shorted to ground... Computer will now think the vehicle is overheated all the time instead of always being in cold start mode, which is what I think it was doing when it was having a hard warm start.

If there was a short to ground on the power/sense wire, then I should not be seeing 5 volts at the power pin and changing temp sensors would make no difference... if there's a short to ground on the ground pin it wouldn't matter since it goes straight to a common ground anyway.

 

Nope, electrically it doesn't make sense does it, lol, all that time we spent learning this stuff to find out it CAN work the other way

So it IS the way it works, it uses what is called a Pull Up resistor circuit(or Pull Down, don't remember which) which causes it to act that way and converts it to digital instead of an analog signal so computer can use it

So voltage goes down with resistance, what a world

But its also that the grey/red wire is the signal return wire, computers common ground reference, used on all the sensors, same grey/red wire at every sensor
The voltage comes from the OTHER wire at the sensor, so it measuring GROUND resistance at the computer connection for each sensor

So 0volts or 0 ohms = very high temp

 

So what have I got here... Correct voltage coming in, proper resistance for the temperature in the sensor, and 0 ohm resistance on the ground wire... Where is the fault? It can't be between pin 38 turn the sensor because I get 5 volt... could be between the sensor and the ground but that would not matter... and it can't be pin 91 because I get readings from all the other sensors and a vehicle runs. I'm stumped.

 

Plot thickens...

I was getting some weird Ohm readings (~3 ohm climbing to 144 ohm in 1 sec) between the ground pin / engine block, and battery (-) ONLY when the key was on and with key off I got < 1 Ohm

Using a jumper cable to add new ground path did not change the weird readings.

I connected a 10K ohm resistor to the 5V terminal of the temp sensor plug and grounded it direct to the battery and got 129F which is correct per your chart.

Now I'm super stumped... I think I can fix the temp reading... but WTF is up with the block/battery resistance readings? Is the key on power flow affecting them?

If that is the case then maybe I have an open ground somewhere else and it's back-feeding through the temp sensor and blew out the old one...

EDIT: important part bolded... weird ohm readings with key on are normal if the battery is still connected, ohm meters don't like stray current... duh. It's been too long since electronics class.

 

ECT's "ground" wire, grey/red wire, is a reference ground inside computer so won't be the same as engine ground, and can change as computer boots up, key on
It is used for the sensors only so computer's digital references for analog voltage is accurate

Battery negative, engine and firewall(computer) grounds should be 0 ohms

 

Ok, i figured out your chart... It's based on probing a working sensor with power flowing. The voltage DROP across the sensor corresponds with the voltage listed on the chart.

 

So I am barking up the wrong tree probing this sensor with the engine not running... wait until the manifold is fixed and the truck is running... got it.

 

Bought another temp sensor, this time it worked perfectly. Must have had a fault in the first new one

The hard restart is gone and the live data shows proper temperature regulation.

Gauges are all correct and I even want to fix the ODO now.

 

Good work

Thank for posting the update

Yes, I remember when "New" meant "tested and works"

Now it just means "no one has touched it, so you test it for us and we will replace it if it doesn't work"