Do you have a scan tool to plug into the OBD port?
Open loop - computer is delivering fuel according to fuel map without regard to o2 sensor feedback...it thinks the engine isn't at the correct operating temp and will keep pumping fuel to stoke the fires up good and hot...which can actually quench the metal in the engine, preventing it from getting hotter (and killing your mileage in the process. That's why I asked if you had recently serviced your cooling system/checked tstat/water level)
Closed loop - ECT (Engine Coolant Temperature) sensor sends signal to the computer so it can monitor for what engineers have determined as correct operating temperature for that engine. when it hits a pre-set temperature, usually just below where your tstat opens, the computer starts to trim fuel injector pulse duration (fuel delivery) according to what the oxygen sensors tell it as far as air/fuel ratio.
If I were to guess, you've either got a tstat that opens at the wrong temperature, or a bad ECT sensor, or not enough coolant in the system.
your scan tool should tell you fuel system status...open is not good if it has been running for a while, and I'd look at the sensor first - see that it's sending correct temp info to the ECU. If it's closed, look at the oxygen sensor info - it should be sending a varying waveform representing the voltage it generates with values between 01. and 0.9Vdc to the ECU. (how the ECU handles the information -whether relying on the analog signal or digitizing it and sending frequencies to the computer, I couldn't tell you for certain on your truck)
I do have a good scan tool to use. As for the temp gauge I do remember people saying that it was a “dummy” gauge and not actually connected to the sensor. But that was not all of them. Only a certain year range and I can’t remember what that was. The needle does reach operating temp before the heat gets fully warm though. So it should be open loop when cold and closed loop when warm?
Well I got curious and explored an app code reader I have since the scan tool is at work, and discovered it does have live data! This screenshot was taken at idle after a drive. I watched it while driving and the coolant temp was a consistent 85-90° centigrade. It would drop a couple degrees as the revs go up on a “hammer down” run and stay about 90 at normal cruise. Is is normal for the fuel trims to be different from bank to bank? The difference would vary from1-4% depending on engine load
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Most temp gauges on cars in the last 20 or so years probably are dummies....if the even have them!
I can't tell about open/closed loop from that screenshot...If it says closed, something is clearly amiss.
The temp is probably right about where it should be...but your fuel trims indicate almost 10% above "normal" so we need to determine why and where the computer thinks the extra air is coming from that it needs to pump more fuel.
you dont have a re-usable filter on the truck, do you? K&N etc? I don't recall from the pic you posted...or was that on the Mini thread?
ok, scantool: what's the intake air temp readout, and is it close enough to the actual ambient air temp? What about a MAP sensor (sometimes called baro, from barometric) readout? (speed-density fuel delivery system might not be doing math correctly based on sensor inputs...can we lose the EFIE while we sort this out?)
As far as being built, no its stock. I can’t remember how far it’ll let me advance it. 10° maybe? I don’t think it’ll affect figuring out fuel trims. I could be wrong though. Still hadn’t gotten around to trying it again without the EFIE. Maybe tomorrow night I’ll find time. Probably won’t be running the mini much anymore since the latest discovery. It most likely will need a rebuild
I tune mine with an analog Voltmeter -I like to see the needle sweep up and down- so that when I'm at hot idle/closed loop, the EFIE is sending the computer 1VDC peaks, metered between chassis ground and the wire that goes TO the computer. (I don't know how your EFIE connects to the computer, but the electronics are inserted into the circuit between what the sensor actually reads and what you want it to tell the computer). I suspect because your fuel trims are +8 or so, your truck's computer is seeing a waveform like the lower left of the examples on that webpage, when it should be seeing one like the upper right. It might be something as simple as you having the wires reversed on the terminals.
It would be interesting to see what the changes are to the o2 signal to the computer with stock timing as well as the modified timing.
Something tells me you're going to get a reading like the upper right diagram on that web page, and you might run into difficulties with the computer trimming fuel delivery back