CTS or ECT
greeting from texas, where its warming up enough to use a/c already.
My suv is a Mercedes Benz ML 430, 2000 vintage. v8, 4.3L, gas hog; 15 mpg mixed city/highway. 4800 lb brick parachute. great truck for pulling my boat, but also my daily driver. still, that seems like a lot of gas to run thru a 260 cu in engine.
square one for me was to experiment with coolant temp sensor. i made some measurements, and tried several values, and THINK i can give some general recommendations for decent starting points.
my ECT sensor reads about 1000 ohms with the engine cold, outside temp 65 deg f. I tried everything from 100 to 2200 ohms. sure enough, resistance too low, it wont start! 'pretty low', fans run too much; too high, no improvement.
on my truck you can see whats going on when you turn the ignition key on, but dont start the motor. with the engine cold, what i THINK you want is to see the temp gauge JUST come up off of zero with the swamping resistor in parallel with the ect sensor. for me, 1500 ohms is just right. the fans come on a little sooner with the a/c on, but thats ok with me as the a/c seems to really cool better.
my proposal, start with a parallel resistor whose value is 1.5 times what you measure with a cold engine.
It makes the dash gauge read high, but thats ok with me. i stuck a candy thermometer in the overflow tank and warmed the engine up, with the cap off and it looks like a nice 160 deg F. (the 'benz runs all the water through the overflow tank). so i KNOW when my dash gauge says 90 dec C (D$@#%$ metric GERMANS!), its REALLY 160-170.
so, this mod is good for me. engine acually runs cooler, ac works better, and the ecm wastes a little less gas.
with some other intial guesses on MAP and MAF series resitors, (still experimenting), already gettting 17 mpg. when they are all tweaked, will add the efie.
good luck to all.