1996 Custom Code ?

Hi all. I have a P0300 code showing on a diagnostic computer. Any help?
Thanks....

This is the OBD-II code for a random misfire. Check your ignition system and replace parts as necessary. I would first check the plug wires. If you somehow got alot of water or moisture in the engine compartment (i.e. washing engine or driving through a deep puddle) could also cause this.

If you have the 3.8L engine then I would also check your coolant level. The 3800 Series II engine is notorious for upper intake plenum warpage over time. This is the plastic part on top of the engine (not the cover). The warpage is caused by the hot EGR system. Coincidentially, a water jacket is nearby and leaks antifreeze into the engine when this occurs. This could definitely cause a misfire, especially above 4000 RPM, when the cooling system pressure rises. If your SES light blinks at high RPMs I would highly suspect this. A blinking SES light usually occurs during a detected misfire if it remains continuous. If the misfire is only intermittent, the SES light will not blink and just remain lit until the next key off-on.

Thank you very much for the info! Very informative... I do have the 3800 series engine. I am actually going to be flushing the coolant system on Thursday of this week. In addition, how do I determine the ignition issues? Check plug wires, sp, etc? Coil packs? Have no idea how to do that though...
Anthony



This is the OBD-II code for a random misfire. Check your ignition system and replace parts as necessary. I would first check the plug wires. If you somehow got alot of water or moisture in the engine compartment (i.e. washing engine or driving through a deep puddle) could also cause this.

If you have the 3.8L engine then I would also check your coolant level. The 3800 Series II engine is notorious for upper intake plenum warpage over time. This is the plastic part on top of the engine (not the cover). The warpage is caused by the hot EGR system. Coincidentially, a water jacket is nearby and leaks antifreeze into the engine when this occurs. This could definitely cause a misfire, especially above 4000 RPM, when the cooling system pressure rises. If your SES light blinks at high RPMs I would highly suspect this. A blinking SES light usually occurs during a detected misfire if it remains continuous. If the misfire is only intermittent, the SES light will not blink and just remain lit until the next key off-on.

Your coil packs are fine. If one (of the three) were bad, then you would get a pair of misfire codes; P301 and P304 (for the cylinder 1 & 4 coil pack) , P302 and P305 (for the cylinder 2 & 5 coil pack), or P303 and P306 (for the cylinder 3 & 6 coil pack). I would replace the spark plugs and wires. If you can afford it, buy the AC Delco platinum plugs. They cost around $6 each and they are the best you can buy for this application. A good, inexpensive alternative would be the regular Bosch Platinum plugs at about $2 each. Of course, make sure you gap them to .060". Don't buy the Bosch Platinum +2 or +4 plugs because they don't work well with your ignition system. Bosch wires are good also. If possible though, once again buy the AC Delco Premium wires. If your car has over 100K miles on it or is nearing this then these parts are due for replacement anyways. Replacing these parts is the least expensive option and will probably fix your problem, assuming that a coolant leak is not causing the misfire. I would also replace the PCV valve while you're at it. These are only $3 or so.

Also, if you are getting a coolant flush I would highly recommend putting the common green antifreeze back in. The orange Dexcool (what is in there right now) sludges up really bad long before its scheduled interval of 5 yrs./150K miles. Any good mechanic will tell you the same thing. I wouldn't be surprised to hear that your mechanic was going to put green stuff in anyways. But of course, make sure ALL the Dexcool gets flushed out because mixing the two coolants would be very bad. If you can afford it, changing the thermostat and all of the coolant hoses and could save you from being stranded due to a blown out hose if you have a lot of miles on the vehicle.