Am I on the right track here? Bad ECT sensor?

So my 92 Ranger with a 4.0 OHV w/ a 5 speed has developed a curious new issue. The truck has been parked for several months and was recently brought out of hibernation.

The issue I'm having is what I believe to be a bad ECT sensor. The truck starts fine, idles a bit high, temp gauge rises into normal area. If I give the truck light throttle, it sputters and dies. If I goose the throttle to about 1/2 it revs quickly without a hiccup, but runs extremely rich, and bellows black smoke.

Driving produces the same result, if I get hard on the throttle, it accelerates normally, but if I try to maintain a speed at light throttle and accelerate slowly, it hiccups and bucks and jerks until I push past it.

From my small amount of understanding on this, if the ECT sensor is bad, it's telling the computer the engine is dead cold, and overfueling for normal operating temps. This would somewhat make sense in that any throttle input would deliver too much fuel for the air being consumed and stall the motor. However opening the throttle body quick enough allows enough air to continue to run.

If someone could let me know if this sounds like I'm way off base or not that'd be excellent. I realize an ECT sensor is a cheap part, I'm just not a fan of replacing parts willy nilly to find the solution. Thanks TRS!!!

Do you have a CEL(check engine light)?

Reason I ask is because the computer has a timer of sorts for the ECT temp sensor, when you start the engine and the ECT sensor shows more than 2volts(cold) then timer starts, if ECT voltage isn't dropping(temp going up) within a few minutes then computer will set a code and turn on the CEL.
There could be a glitch in the system so ECT is not off the table as the problem.

More common failure of ECT is when it shows warm, 1volt or less all the time, computer thinks engine was just restarted, so engine struggles to run cold but then after warming up runs fine.
Computer doesn't turn on CEL because it just thinks you drive alot, lol, never letting the engine cool off.

ECT can be tested with volt or ohm meter, 5volts goes in on 1 wire and less than 5 volts comes out on the other, 3 volts cold engine and .5volts fully warmed up.
Or low OHMs cold, high OHMs warm

Cold idle should be 1,100rpm
Then slowly drop to about 700 within 5-8 minutes
That would mean ECT sensor is working, as the cold idle is based solely on ECT voltage, higher volts = higher idle, as ECT voltage drops so does the idle

Computer should open IAC(idle air control) valve all the way each time you start the engine, so idle should go up to 1,500rpm then drop to 1,100 or 700 depending on engine temp(ECT).
IAC valve could be sticking a bit after sitting for so long.

I would check the Fuel pressure regulator(FPR) on the fuel rail.
It is on the passenger side top front of lower intake, it has the Fuel Return line attached and a Vacuum Hose, if the diaphragm in the FPR leaks, raw fuel is sucked into the intake via that vacuum line, so remove that vacuum hose and check it for fuel, replace FPR if fuel is found in that hose.

Could also be sticking injectors, not closing tightly so dripping fuel, fuel can get "gummy" after sitting, run a can of Seafoam in the tank and see if that helps.

While it doesn't read like a MAF issue it is always a good idea to clean MAF sensor once a year on the 4.0l engines, MAF data is what computer bases 14:1 air:fuel ratio on, MAF issues usually show as Lean issue not rich.


If you decide to replace the ECT sensor, make sure they give you the SENSOR, not the SENDER.
The temp gauge in the dash uses a ONE wire sender, and it is often called ECT(engine coolant temp) sender, parts guys can get that wrong.
You want the TWO wire ECT sensor.