P305 Error Code

[stilts07]

My 2000 Pontiac Firebird 3.8 has been misfiring and throws off p305 on carmd. I changed the spark plug, unsnapped the wire from the coil pack and spark were flying so i know it had electricity. So other thing i know is to think it might be clogged injector. I went to walmart and bought a STP brand all purpose engine cleaner and the check engine light came off for about 10 minutes then it started right back up. How do i find out how to fix this without having to take it to the shop and spend thousands on a minor problem? How much longer should i drive the car like this? PLEASE HELP!

[maxwedge]

Do you have good spark at that plug? Check the resistance of that injector, should be about 11 ohms.

[Tech II]

My 2000 Pontiac Firebird 3.8 has been misfiring and throws off p305 on carmd. I changed the spark plug, unsnapped the wire from the coil pack and spark were flying so i know it had electricity.

Well P0305, means you have a misfire on cylinder #5.....So you changed the plug.....the plug you took out, you are sure it was #5? Was it fouled or wet? The way you check for spark on a cylinder is with a spark tester.....you remove the wire from the plug, attach the spark tester and start the car.....if the tester has a healthy spark, then ok.....one coil fires two plugs....in your case, this is the 5/2 coil.....so, with ignition off, you should remove the tester, reattach the wire to the #5 plug, and then disconnect the ignition wire from the #2 plug, and attach the wire to the tester....start the car and look for a healthy spark.....If you have a healthy spark in both cases, then the coil and wires and plugs are ok.....if you don't have a good spark, it could be a bad coil or wire.....just for ha-ha's, did you remove the ignition wires from the #2 and #5 coil terminals? Was there carbon/corrosion on either terminal? If there was, the wires should be replaced and if the terminals can't be cleaned with light sanding, then the coil should be replaced, also.....more often than not, a misfire on these engines is a bad coil, wire, or plug.....there was TSB out there for a possible carbon tracking problem between the insulator of the plug and the boot of the ignition wire......if that is the case, the plug AND wire should be replaced(do them all, probably needs a tuneup anyway)....



So other thing i know is to think it might be clogged injector. I went to walmart and bought a STP brand all purpose engine cleaner and the check engine light came off for about 10 minutes then it started right back up.

If an injector is bad, those treatments generally don't help.....injector cleaner that you put in the gas tank, is only good for Maintenance purposes....once the injector is clogged, the horse is out of the barn......if this is the case, only using a professional cleaning setup at the fuel rail might work.....the other possibility is the injecor is not plugged, but has a bad coil in it.....a way to check for a bad injector, if you don't have expensive test equipment, is remove the injector from the rail and swap it with another injector, say #3 injector......if the problem moves to cylinder #3, then you know it's the injector...




How do i find out how to fix this without having to take it to the shop and spend thousands on a minor problem? How much longer should i drive the car like this? PLEASE HELP!

Wow, thousands of dollars for a misfire? Must have had some bad experiences.....Like I said the usual cause of a misfire is coil, wire, or plug.....a bad wire can be arcing to ground causing a misfire......if you can easily trace the wires, start the car at night....look under the hood in the dark, and see/hear a spark...concentrate on #2 and #5 wires.....

You do not want to drive a vehicle like this......when the misfire is happening, the CE light will come on.....If the CE light "flashes", that means the misfire is so bad, that the misfire could cause potential damage to the catalytic converter(big bucks)....when you drive with a misfire, unburned fuel is entering that hot cat, and it's like adding fuel to a fire......the heat will rise in the cat and could melt the catalyst, and plug the exhaust system.....

A tuneup, which is what I think your car needs(air filter, fuel filter, pcv, plugs(use A-C Delco only) and wires), should be around $200-$250...

There is one more possibility......if the coil, wires and plugs are ok, and the injector is ok and is firing correctly, then you could have a mechanical problem.....this could be an engine compression problem caused by a bad valve.....

My money is on a tuneup....

[j cAT]

Originally Posted by stilts07

My 2000 Pontiac Firebird 3.8 has been misfiring and throws off p305 on carmd. I changed the spark plug, unsnapped the wire from the coil pack and spark were flying so i know it had electricity. So other thing i know is to think it might be clogged injector. I went to walmart and bought a STP brand all purpose engine cleaner and the check engine light came off for about 10 minutes then it started right back up. How do i find out how to fix this without having to take it to the shop and spend thousands on a minor problem? How much longer should i drive the car like this? PLEASE HELP!

car md is your very basic coder reader. with a diagnostic reader they/you can see the misfires and the amount of them. this is helpful in determining the cause.

most DIY people swap the plug/wire/coil/injector one / each at a time reset computer and retest for the code to change. then you know where the problem is .. if after swapping these items no change then this may be gasket failures. examples are coolant ingestion /vacuum/intake leak/valve spring / burnt valve [from running too lean] ....

your concerns are real this maybe expensive to fix. so be sure you/the repairs know for sure what's wrong before they start replacing parts at your expense...............

just to be sure about the fuel pressure being correct this should also be measured .. if borderline low this may show as this 305 code...so make sure you have proper fuel pressures and the regulator is working correctly and you have no injector fuel leak down .. DO THE FUEL PRESSURE TEST...