Question about Mitsubishi Galant

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Timing belt broke bent valves got a remaned head,installed head new belt also found broken balance belt replaced it also. engine wouldnt start checked belt timing all marks were perfect pulled #1 plug checked for tdc perfect checked for ign good spark checked fuel pressure 70lbs checked injectors with a node lite ok.still no start only fire once or twice per revolution. changed crank sensor.still no good changed the cam sensor distributor with a new one. now it will start not good and run but it wont rev up and the exhaust manifold turns red and it sounds like the engine is running retarded. disconnected the exhaust at the manifold to see if it was a plugged system all clear .help! whats wrong ?

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  • davec779 Mar 16, 2011

    its a1998 gallant 4.2 i have a snapon scanner and i got a throttle posiyion sensor code we installed a new one no change scanned no codes we also changed the ecm with a good used one no change no codes. the engine sounds like its really retarded ether from ign or valve timing. when the throttle is opened it will gain rpms up to 2200 but it is very slow and sounds like it is under a big load. im stumped please help!



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Hi!!This occurs when the ignition timing and fuel mixture are changed causing an excessive amount of heat. If the engine is running on a VERY lean or rich mixture, the temp will be so high to make the exhaust manifold glow red,. which would damage the catalytic converter making things worst.
You did not provide the vehicle's year and model, but, you should have DTCs stored in the PCM memory. Scan the computer for Trouble Codes and you'll find out if the mixture is in the lean or rich side and you can make the necessary adjustments. AutoZone, Checkers and similar auto parts stores let you borrow DTC Scanners.
Good Luck!! A HELPFUL - 4 THUMBS - rating for this solution would be greatly appreciated. Thank you for using FixYa.

Posted on Mar 16, 2011

  • Rene J Solis Mar 16, 2011

    The most important information for measuring engine fuel requirements comes from the Manifold Absolute Pressure (MAP) sensor. Using the pressure and temperature data, the PCM calculates the intake air mass. It is connected to the engine intake manifold and takes readings of the absolute pressure.

    Atmospheric pressure is measured both when the engine is started and when driving fully loaded, then the pressure sensor information is adjusted accordingly.

    The Oxygen (O2) sensor is a device which produces an electrical voltage when exposed to the oxygen present in the exhaust gases. The sensor is mounted in the exhaust system, usually in the manifold or a boss located on the down pipe before the catalyst. The oxygen sensors used on some models are electrically heated internally for faster switching when the engine is started cold. The oxygen sensor produces a voltage within 0 and 1 volt. When there is a large amount of oxygen present (lean mixture), the sensor produces a low voltage (less than 0.4v). When there is a lesser amount present (rich mixture) it produces a higher voltage (0.6-1.0v). The stoichiometric or correct fuel to air ratio will read between 0.4 and 0.6v. By monitoring the oxygen content and converting it to electrical voltage, the sensor acts as a rich-lean switch. The voltage is transmitted to the PCM.

    Some models have two sensors, one before the catalyst and one after. This is done for a catalyst efficiency monitor that is a part of the OBD-II engine controls. The one before the catalyst measures the exhaust emissions right out of the engine, and sends the signal to the PCM about the state of the mixture as previously talked about. The second sensor reports the difference in the emissions after the exhaust gases have gone through the catalyst. This sensor reports to the PCM the amount of emissions reduction the catalyst is performing.

    The oxygen sensor will not work until a predetermined temperature is reached, until this time the PCM is running in what as known as OPEN LOOP operation. OPEN LOOP means that the PCM has not yet begun to correct the air-to-fuel ratio by reading the oxygen sensor. After the engine comes to operating temperature, the PCM will monitor the oxygen sensor and correct the air/fuel ratio from the sensor's readings. This is what is known as CLOSED LOOP operation.

    A Heated Oxygen Sensor (HO2S) has a heating element that keeps the sensor at proper operating temperature during all operating modes. Maintaining correct sensor temperature at all times allows the system to enter into CLOSED LOOP operation sooner.

    In CLOSED LOOP operation, the PCM monitors the sensor input (along with other inputs) and adjusts the injector pulse width accordingly. During OPEN LOOP operation, the PCM ignores the sensor input and adjusts the injector pulse to a preprogrammed value based on other inputs.

    The Intake Air Temperature (IAT) sensor determines the air temperature entering the intake manifold. Resistance changes in response to the ambient air temperature. The sensor has a negative temperature coefficient. As the temperature of the sensor rises the resistance across the sensor decreases. This provides a signal to the PCM indicating the temperature of the incoming air charge. This sensor helps the PCM to determine spark timing and air/fuel ratio. Information from this sensor is added to the pressure sensor information to calculate the air mass being sent to the cylinders. The IAT receives a 5-volt reference signal and the signal return is based upon the change in the measured resistance due to temperature.

    The Engine Coolant Temperature (ECT) sensor resistance changes in response to engine coolant temperature. The sensor resistance decreases as the coolant temperature increases, and increases as the coolant temperature decreases. This provides a reference signal to the PCM, which indicates engine coolant temperature. The signal sent to the PCM by the ECT sensor helps the PCM to determine spark advance, EGR flow rate, air/fuel ratio, and engine temperature. The ECT is a two wire sensor, a 5-volt reference signal is sent to the sensor and the signal return is based upon the change in the measured resistance due to temperature.

    The Mass Air Flow (MAF) sensor directly measures the mass of air being drawn into the engine. The sensor output is used to calculate injector pulse width. The MAF sensor is what is referred to as a "hot-wire sensor". The sensor uses a thin platinum wire filament, wound on a ceramic bobbin and coated with glass, that is heated to 417°F (200°C) above the ambient air temperature and subjected to the intake airflow stream. A "cold-wire" is used inside the MAF sensor to determine the ambient air temperature.

    Battery voltage, a reference signal, and a ground signal from the PCM are supplied to the MAF sensor. The sensor returns a signal proportionate to the current flow required to keep the "hot-wire" at the required temperature. The increased airflow across the "hot-wire" acts as a cooling fan, lowering the resistance and requiring more current to maintain the temperature of the wire. The increased current is measured by the voltage in the circuit, as current increases, voltage increases. As the airflow increases the signal return voltage of a normally operating MAF sensor will increase.

    Check the above named sensors, make sure all the vacuum hoses are connected and on the right place. I am puzzled about not getting any codes, make sure all the sensors, wiring and fuses are OK. Keep me posted



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