I have a 96 hevrolet 1/2 ton Z-71 with about 150K miles on it. I have been in the Navy in San Diego for the last 3 years and the truck past their emission test. I just finished serving my duty and headed back to Texas and the CHECK ENGINE LIGHT came on. I had the codes read and they were
300 and 340. I have replaced all the O2 sensors, wires, dist cap, cam sensor, and still have it reading the same codes. The only performance problem is a very slight miss at idle. Driving back the performance and mileage were normal. Please help me diagnose this problem. Please respond to me by e-mail, since I am posting this on a friends computer, using my e-mail address.
Service bulletin: #PI00149D 4.3 L35 LU3 , 5.0 L30 , 5.7 L31 Engines that May Exhibit a MIL With a P0300 Set - DTC hard throttle miss misfire - (Dec 18, 2003)
DTC P0300 Engine Misfire Detected The crankshaft position (CKP) sensor and the camshaft position (CMP) sensor are used in order to detect an engine misfire. The VCM monitors the speed of the crankshaft. The VCM detects a deceleration of the crankshaft that is not associated with a normal engine speed reduction. In order to determine if a misfire occurred, the VCM compares the deceleration information to the engine speed and the engine load. If a misfire event is determined, the VCM compares the crankshaft position to the cam sensor signal in order to determine which cylinder misfired. The VCM stores the information in separate accumulators for each cylinder. Upon completion (or failure) of the test, the VCM evaluates the number of misfires in each accumulator. If the accumulators are somewhat even or if 3 or more cylinders are misfiring, then this determines that a random misfire has occurred. The VCM also utilizes the input from the ABS wheel speed sensor in order to determine if a rough road condition exists which could cause a crankshaft acceleration and deceleration. If a rough road condition exists, the diagnostic will not run. This DTC is a type B DTC.
The following conditions will set the DTC: # 25 cycles have elapsed since Transmission shift (automatic only) # No TP sensor DTCs # No MAF sensor DTCs # No IC sensor DTCs # No VS sensor DTCs # No Crankshaft Position sensor DTCs # Rough road is not detected. # The ECT is between -6.75° C and 95.2° C. for the 5.0L, 5.7L # The ECT is between -6.75° C and 129° C. for the 7.4L # The engine speed between 300 RPM and 5600 RPM for the 5.0L, 5.7L # The engine speed between 300 RPM and 4900 RPM for the 7.4L # The system voltage between 9 volts and 16 volts # The positive throttle position change is less than 4.9% for 100 msec. # The negative throttle position change is less than 2.9% for 100 msec. # A misfire is detected.
DTC P0340 Camshaft Position (CMP) Sensor Circuit The Camshaft Position (CMP) sensor is used to indicate the camshaft position. The VCM uses the CMP sensor in order to determine which cylinder is misfiring. This DTC is also used to check for a properly installed High Voltage switch. This is a type B DTC.
The follow> I have a 96 hevrolet 1/2 ton Z-71 with about 150K miles on it. I have > been in the Navy
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