1999 Chevy Astro DTC/PO300

Tiny
MTRDUDE
  • MEMBER
  • 1999 CHEVROLET ASTRO
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 366,000 MILES
VIN #1GCDM19W7XB149698

Getting trouble code #'s PO121/305/420/1870/420 pending. The DTC giving me freeze frame info is PO300 (random multiple cylinder misfire detected). I have an Actron generic scanner and can read the codes and freeze frame data but don't have any diagnostic capabilities and need some suggestions based on the FF data below.
THROTTLE POSITION) 1.9
ENGINE RPM) 858
LOAD VALUE) 2.7
MAP SENSOR) 33
AIR FLOW RATE) 5.34
COOLANT TEMP) 194
SHORT TERM FUEL TRIM 1) 14.0
LTFT1) 25.0
STFT2) 0.0
LTFT2) 13.2
STFT3) -57.5
LTFT3) 56.2
STFT4) 57.0
LTFT4) 17.1
VEHICLE SPEED) 7
FUEL SYSTEM 1) CLOSED
FUEL SYSTEM 2) CLOSED
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Wednesday, August 19th, 2009 AT 5:52 AM

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Tiny
BMRFIXIT
  • EXPERT
Start by checking fuel pressure and check for tune up
coil is a common failure check it too

Cylinder # 5 is misfiring
TPS sensor may have a problem and need to be checked
catalyst at max

DTC P0300: ENGINE MISFIRE DETECTED (4.3L "L", "M", "S" & "T" SERIES)

Misfire is detected using Camshaft Position (CMP) and Crankshaft Position (CKP) sensors. When VCM senses CKP deceleration not associated with normal engine speed reduction, CMP is used to determine misfiring cylinder. VCM determines misfires on each cylinder, evaluates a random misfire, and sets DTC. Conditions for setting DTC:
No CKP, IAC, MAF, TP or VSS sensor DTCs set.
Rough road not detected.
Engine speed 300-5600 RPM.
ECT at normal operating temperature.
System voltage 9-16 volts.
Positive or negative throttle position change is less than 2.9 percent for 100 msec.
A misfire is detected.
Diagnostic Procedures
Perform On-Board Diagnostic (OBD) system check. After performing OBD system check, go to next step.
Review FAILURE RECORDS data.
If other DTCs are stored, diagnose affected DTCs.
If no other DTCs are present, go to next step.
Perform CKP System Variation Learn Procedure.
After performing CKP learn procedure, go to next step.
Start and allow engine to idle.
Using scan tool, monitor MAP sensor voltage.
If voltage reading is greater than 4 volts, go to DTC P0108 for diagnosis. If voltage reading is not greater than 4 volts, go to next step.
Turn ignition off, then turn ignition on, with engine off. Duplicate conditions required to set DTC. Using scan tool, read DTC PRESENT THIS IGNITION CYCLE. If the scan tool displays DTC P0300, PRESENT THIS IGN, go to next step. If the scan tool does not display DTC P0300, PRESENT THIS IGN, go to step 11.
Using scan tool, review misfire index. If misfire index is increasing for more than one cylinder.
Check spark plug, wire and injector
If misfire index is not increasing for more than one cylinder, go to next step.
Install a spark tester on No. 1 spark plug wire. Disconnect fuel injector harness at intake manifold. Crank engine and check for spark at tester. Repeat procedure for each spark plug wire. If spark is adequate on all wires, go to next step. If spark is not adequate, diagnose ignition system.

Remove and check spark plugs for wear, excessive gap, cracks or fouling. If spark plugs are okay, go to next step. If spark plugs are not okay, go to step 12.
Perform cylinder compression test. If engine mechanical problem is found, repair as necessary. After repairs, go to step 14. If no mechanical problem is found, go to next step.
Perform injector circuit test. See appropriate BASIC DIAGNOSTIC PROCEDURES article. If fuel system is okay, go to next step. If fuel system is not okay, go to step 13.
DTC is intermittent. Check if additional DTCs are present. Diagnose affected DTCs. If no additional DTCs are present, see DIAGNOSTIC AIDS.
Replace spark plugs. After replacing spark plugs, go to step 14.
Repair as necessary. After repairs, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start engine and allow it to reach operating temperature. Using scan tool, select DTC, SPECIFIC function and enter this DTC. Operate vehicle within conditions required to set DTC. If scan tool indicates that this DTC RAN AND PASSED, go to next step. If scan tool does not indicate that this DTC RAN AND PASSED, repeat step 2.
Using scan tool, select Read and Record INFO, REVIEW INFO function. Check if any undiagnosed DTCs are displayed. Diagnose affected DTCs. If no additional DTCs are displayed, system is okay.
Diagnostic Aids
A misfire could be caused by excessive vibration from sources other than engine. Check following items for possible cause of misfire: tire/wheel out of balance/round, uneven brake rotor or drum surface, or a rough road condition. Check plug wires for proper installation and operation. Check fuel level, condition and quality
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Wednesday, August 19th, 2009 AT 6:21 AM

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