a good tune up may fix this problem.....new plugs,wires,rotor and distributer cap...do it all at the same time
I have already replaced the plugs, cap, rotor and plug wires (all at the same time) and the problems remain. Also replaced fuel filter at the same time.
Even if plugs, wires, cap and rotor were faulty, the symptoms would not go away while under full throttle or while driving up hill. So the suggestion of tune up with cap, rotor, wires and plugs doesn't help me.
let ne send you a chart to break down the problem...a egr valve could cause this at low rpm's
CIRCUIT DESCRIPTION The Crankshaft Position (CKP) sensor is the primary input to determine if misfire is occurring. Engine misfire is detected by monitoring crankshaft speed variations between cylinders. If a crankshaft deceleration occurs during a combustion or power stroke, the control module will compare this change in crankshaft speed to the previous cylinder. If the crankshaft speed change is more than a maximum allowable speed, the misfire is detected. Misfire may occur in a specific cylinder or in all cylinders randomly.When an engine is misfiring, brief decelerations in crankshaft rotational speed will be detected by the CKP. The control module determines which cylinder has misfired based upon the Camshaft Position (CMP) sensor input. Misfire data is stored for each cylinder in separate accumulators. After 100 combustion events, the misfire totals are compared to a calibrated maximum number. If the misfire is excessive, this Diagnostic Trouble Code (DTC) will set.CONDITIONS FOR RUNNING THE DTC IMPORTANT: If start-up ECT is below -7°C (20°F) , misfire detection is delayed until ECT is more than 21°C (70°F) . If start-up ECT is more than -7°C (20°F) , misfire detection begins after a 5 second delay.
CONDITIONS FOR SETTING THE DTC The VCM detects a deceleration in the crankshaft speed characteristic of either an emission type misfire or a catalyst damaging type misfire.ACTION TAKEN WHEN THE DTC SETS If the VCM determines that the engine misfire is significant enough to have a negative impact on emissions, the VCM turns ON the Malfunction Indicator Lamp (MIL) after the misfire has been detected on 2 non-consecutive trips under the same operating conditions. If the misfire is severe enough that catalytic converter damage could result, the MIL flashes while the misfire is present.CONDITIONS FOR CLEARING THE MIL OR DTC
DIAGNOSTIC AIDS The Misfire Index counts the number of misfires. The scan tool can monitor the Misfire Index. There is a current and history misfire counter for each cylinder. Use the current misfire counter in order to determine which cylinder is misfiring or use the history misfire counter for misfires that are not currently present. Many different condition could cause an intermittent misfire.Check for the following conditions:
An intermittent may be caused by any of the following conditions:
Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Diagrams.If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Diagrams.
i will opt out
I have an intermittent problem with my 2000 Chevy Astro with the 4.3 Vortec V6. Sometimes it runs fine, sometimes there is a bad stumble at cruise speed. Goes away under full throttle or going up hills. Misfire and stumble resumes on downhill or on level ground. Code scanner reveals code P0300, Random Cylinder Ignition Misfire. Also tends to run very rich at random occasions. What is going on with this, and how do I fix it? What would cause the intermittent random misfire when the engine is under low load?
I have already replaced the distributor cap, rotor, plug wires and spark plugs, as well as the fuel filter but this didn't fix the problem. I need to know specifically what components to look at to try to fix this, as I don't have the money to start replacing components one at a time until the problem goes away.
If I have a fuel delivery issue, why would the OBDII scanner indicate a Code P0300, random cylinder misfire and not indicate a fuel delivery trouble code?
I spent all afternoon checking out various sensors and components according to my Haynes service manual. I checked the coolant temperature sensor, intake air sensor, crankshaft position sensor, MAP sensor, MAF sensor, EGR valve, and camshaft position sensor. Also checked the coil for cracks and found nothing wrong with it. When the engine runs poorly, it acts like a vacuum leak but I can find no vacuum lines or hoses on this engine to check. Everything on this engine (4.3 Vortec V6 with CMFI injection system) seems to be either electrically or electronically operated.
Every thing checked out fine according to the manual except for some erratic readings from the camshaft position sensor. Could a camshaft position sensor cause a code P0300 Random Cylinder Ignition misfire, and be an intermittent problem? Could this cause the engine to run rich also?
A few months back I replaced the distributor cap, rotor, wires, spark plugs and also the fuel filter all at the same time but none of this helped the problem. I'm running out of things to check... What else could I check that could cause intermittent problems with random ignition misfire and random running excessively rich? Are there any TSB's or other known problems on the 2000 AstroVan for problems like this?
I plan to go later and buy a new camshaft position sensor and install it to see if that fixes the problem.
But if I replace the camshaft sensor and that does not fix the problem, what would you suggest would be the next thing to look at that would cause these problems?
Ok. But given that the van seems to run much better under heavy load or under full throttle, would you say that we could rule out bad compression or weak cylinders or primary ignition failure?
Is there a special fuel pressure gauge that I need for checking fuel pressure on a GM?