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I have an Australian model Ford AU Falcon 1999 model. It's an inline 6 cylinder 4ltr petrol engine.
Since purchasing has been running very rich. Identified 2.7 bar fuel pressure regulator was running at 4.8 bar. Replaced fuel pressure regulator and fuel trims have normalised and fuel consumption has decreased as expected.
Still have an odd issue. Coolant temp reads correct on scan tool from ambient until approximately 165 deg F (about 5 mins of operating at idle). Scan tool will then show an immediate drop to approx. 10 deg F and fluctuate about 5 dergress either side of this figure. The system stays in closed loop and seems to run ok. The vehicle has one coolant temp sensor and the instrument cluster displays correct temp on the analogue dial and live data on scan tool shows what I believe to be an accurate engine temp on the scan tool consistent with the cluster. Given it has one coolant sensor I am at a loss as to how the ECU live data is showing such a wildly false figure.
Subsequent ignition off and on cycles continue to show this 10 deg F temperature at the ECU but cluster is correct until the vehicle completely cools down for which both ECU and cluster will display accurate temps until about that 5 minute mark and ECU temp will drop again.
Since replacing fuel pressure reg it is now entering closed loop fuel injection for which coolant temperature should be one of the inputs dictating whether the system will enter closed loop operation. I did notice after about 15 minutes of driving with the low coolant temp data the system dropped out of closed loop and into open loop operation but still seemed to drive fine.
Any ideas on this one guys?
(also getting a Knock sensor circuit error, I have just replaced the knock sensor and do not know yet if that has solved the P0325 Knock Sensor #1 - Circuit Malfunction.)
I would suggest the instrument cluster is showing a substituted value, on most of the instrument clusters I see the readings for temperature and pressures are not much to do with the actual readings but are designed not to alarm the driver unless something is really wrong. i know of models a very famous German manuafacturing group that a have temperture gauges that remain centred on "N" from 75c to 115c
I from your description I would suspect a break in the wire running to the sensor or a deffective sensor All the automotive coolant temperature sensors I have encountered are what is called NTC Thermistors. At low temperatures these NTC Thermistor have a high resistance which drops rapidly as temperature rises. A comon Ford type may have 6,000 ohms ressistance at freezing point, 2,500ohms at 68f and 300 ohms at 170f.
The correct way to test this circuit is to start by checking the refrernce voltage and ground and the themperature sensor with the sensor both plugged and unplugged .
The simplest way with limited tools and expeience to track the fault down is carefully examine the wiring to the sensor and the plug and gently tug at the wiring looking for breaks. Then test the car from cold if no change. Try subsituting a resistor of around 500 ohms for the temperature sensor and see what happens, this should be enough to tell you if the fault is in the sensor, wiring or ECU.
Because the fault is temperature dependant the most likely suspect is the temperature sensor itself.
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