Question about 1999 Dodge Durango
IN the absence of any codes being stored there are a few things to check for:-
1) Coolant temperature. When the engine is cold at start up this sensor rads @cold' and this signal causes the CM to extend the injection cycles to enrich the ignition mix. If this sensor fails to detect that the engine reaches running temperature the injection cycles will be longer than necessary and this will drink gas. How to check? Most often the coolant sensor is quite
separate to the temperature sender, so a correct read-out on the dash
board does not necessarily indicate correct sensor function. Using a
voltmeter the resistance across the electrical terminals on the sensor can be
measured. By removing the device from
the car and putting the end of the sensor in a pan of hot water it should be
possible to see an immediate change in resistance, it does not matter so much
that the resistance goes up or down but that there is a discernable change with
change in temperature. Generally high
resistance equates to cold temperatures and vice versa. If there is no resistance
change commensurate with temperature change then the sensor is at fault. If there is simply no resistance measurable
(open circuit) then the sensor is at fault. If the sensor is working correctly
check the connector, the wiring and the wiring insulation for faults and
2) Manifold Absolute Pressure sensor. If the MAP sensor is not performing well, it does not need to actually fail, then the faulty signals again lead to the PCM setting increased injection cycles.How to Check? The device has three electrical pins, one for 5 volts reference, one for 0 volts ground and the third (the middle one generally) is the 'signal' output. Put a voltmeter positive connector on the 'signal' pin of the connected socket (back probe by inserting a bit of wire). Apply suction to the vacuum input, even sucking on it with your mouth, should result in a measurable voltage output. At normal air pressure (open throttle) the voltage seen should be 0 volts. As vacuum is applied the voltage output should change to about 5 volts (throttle closed at idle). If no transition seen the MAP is faulty.
3) Fuel Pressure Regulator. If the diaphragm has cracked then fuel might be added via the vacuum line into the Inlet plenum. How to check? When the engine is at idle, disconnecting the vacuum line to a healthy FPR should result in a temporary surge in engine revs for a few seconds as the immediate loss of vacuum to the FPR causes an immediate build up in fuel pressure. At each injection cycle a little more is injected causing the engine to build up revs. In the next few seconds the gradual ingress of unmetered air into the plenum, also caused by the disconnected vacuum tube, begins to upset the stable idle of the engine. The engine will suffer from rough idle until the vacuum line is reconnected. Most of the injection inputs will be crudely governed by signals received from the MAP sensor and feedback from the oxygen sensor.
Posted on Mar 17, 2011
When was last "healthy" tune up? Plugs, wires, all fluids & filters - especially fuel filter??? I'd start there and run a good fuel system cleaner through it and avoid cheap gas.
Posted on Mar 17, 2011
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Posted on Jan 02, 2017
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