1998 and up Rangers use 60-70psi fuel pressure on a Returnless setup
Earlier used 30-40psi return setup
IAC valve is a learned control, it can vary from engine to engine and manual and auto trans
Computer has pre-set "target" idle RPMs, based on engine temp data from ECT sensor.
On cold engine, 65degF, "target" RPM might be 1,100rpm
Computer learns where the IAC Valve needs to be moved to to set each target RPM and remembers that, but as engine mechanics change it constantly "reLearns" that setting.
If you install a new IAC Valve you may notice the idle RPMs wander a bit for a few days/drive cycles, that's the computer reLearning the correct settings for the new IAC Valve.
If you switch MAF data to gm/sec(grams per second) at warm idle you should see engine displacement, i.e. 2.3, 3.0, 4.0, 5.0, ect.......
But that is based on 600-650 idle RPMs
MAF measures air flow into engine so obviously the higher the RPMs the more air will be pulled in, so the higher the gm/sec
MAP data is only used at startup, key on, it is for elevation, higher elevation means thinner air so less fuel can be added.
MAF sensor also compensates for this, thinner air shows up in MAF sensor data because it doesn't "cool the wire" as much as thicker air.
On older pre-MAF sensor computers the MAP sensor was primary sensor for air/fuel mix, now it is just used to set elevation on startup.
TPS spec. is under 1volt closed above 4.5volts WOT, this is also a learned sensor.
ECT sensor is an analog variable resistor, it is sent 5volts from computer, it's Return voltage tells computer the coolant/engine temp.
65degF should show about 3volts on Return wire
200degF, .5volt, operating temp should be 190-200degf
So warmer coolant = lower voltage
Where the ECT sensor is located in the cooling system will also be a factor in what temp is seen, on or very near upper radiator hose will be the hottest part of cooling system after engine warms up.
Thermostat is usually 190-195degF, this means when coolant in engine gets to 190degF the wax in the thermostat melts and it starts to open, this lets hot coolant flow out of the upper radiator hose and into the radiator, forcing cooler coolant from radiator into engine via the lower hose, when this cooler coolant gets to thermostat and it is under 185degF then thermostat will close again, this goes on until a constant temp is reached, it can vary by engine load but should be stable at about 195-200degF during normal driving.
IAT(intake air temp) sensor uses same table of temps to voltage but obviously doesn't get as hot, lol, generally it will have between 2v and 4volts
IAT is part of MAF sensor.
EGR system is only used when engine is under a load, it lowers NOx emissions.
NOx emissions spike when cylinders get hot, cylinders get hot when engine is under load.
Engines can/will ping/knock on regular gas as cylinders heat up, so EGR system has the added benefit of reducing pinging/knocking under load.
Newer EGR system use a DPFE sensor to tell if EGR valve is opening and how far.
DPFE(differential pressure feedback) sensor uses 2 hoses to the exhaust manifold, one close to EGR valve and one farther away, as EGR valve opens there will be a pressure difference between the 2 hoses, the computer has a "lookup" table for this difference so it can tailor the exhaust flow into the intake for the engine load.
Because EGR system can get build up inside, using a pressure differential to calculate exhaust flow can compensate for changes over the years.
Warmed up engine RPM is based on a few things, manual or automatic trans have different "target" idles.
When you put an automatic in gear the idle will increase on IAC valve % but might remain the same on Tach
When AC is turned on idle RPM will increase
Computers have REV Limiters when speedometer is a 0MPH and/or automatic is in PARK/NEUTRAL, at about 3,000rpm the fuel/spark will start to be cut off
Spark timing is not adjustable with distributorless systems
10deg BTDC is common baseline.
18-20deg at idle, but it can vary quite a bit for emissions reasons from engine to engine.
Last edited by RonD; 04-16-2016 at 02:55 PM.