Pontiac grand prix p0300 code

Ok, so I had a code before that told me that my injector #3 had a miss fire. I drove around with it like that for a while and just replaced the #3 injetor yesterday. I'm now smelling gas and blowing smoke when I accelerate. My OBDII scanner now say's P0300 multiple/random miss fire. Any suggestions on what to do, what to look for, and or try? :confused:


P.S. My car is a 2000 Pontiac Grand Prix GTP (Supercharged).

Most common cause for PO 0300 is plug wires worn out and arcing to ground

But would that explain the smoke out of my tail pipes and the smell of gasoline?

But would that explain the smoke out of my tail pipes and the smell of gasoline?

Yes, unburnt fuel in the cyclinder.

If you were not smelling gas before, recheck your work....you had to pull that fuel rail...check that you don't have a fuel leak, especially where the fuel rail connects to the fuel lines.....

What color is the smoke? White? Black?

If you were not smelling gas before, recheck your work....you had to pull that fuel rail...check that you don't have a fuel leak, especially where the fuel rail connects to the fuel lines.....

What color is the smoke? White? Black?


I'm going to check my work but for the smoke I really didn't pay attention to the color. Since it was just a little bit of smoke I really couldn't tell. Are the different color of smoke going to tell me something?

OK, so I've gone back and double checked my work. I couldn't find a gas leak, I also cleaned my IAC sensor, MAF sensor, an the TPS sensor. Now my obdII scanner is reading a P0303 #3 misfire and not the P0300 multiple misfire. Oh and the smoke is white that's coming out of my tailpipes. I looked at my spark plug wires and they look good and are only about a year old. Should I start by changing my spark plug or plug wire? Any ideas on what to do now?

Have you checked for spark from 6/3 coil?

Have you checked for injector pulse on the Number 3 harness with a noid light?

Are you losing any coolant?

I don't know how to check for a spark or how to check for an injector pulse and no I'm not losing any coolant. How do you check for the spark and check for a pulse? Sorry but I'm still learning a lot on how to work on cars in general.

I guess it's the original condition.http://denver.ukmerritt.com/03.jpg

You check for spark with a spark tester......basically you remove the ignition wire from the #3 plug, attach the spark tester to the wire and ground it, and then you start the car and look for spark from the tester......then do the same to the companion cylinder, #6.....

You will need to buy a "noid" light.....remove the harness to #3 injector, and attach the noid light to the harness....start the car, and you should see a flashing light.....no light or a steady light is a problem....

If both are ok, then the next thing you want to do is buy a can of carb cleaner.....with the car running, spray the carb cleaner along the joint of the upper plenum and top of lower intake.....if you spray in the joint and the idle changes, you have a vacuum leak......I have seen the gasket in this joint crack/break, causing the vac leak.....

If that is ok, then you are going to have to do a compression test......you will need to buy a compression tester......

Or, instead of buying all those testers, bring it to a GM shop, which should be able to diagnose it in less than an hour....the longer you drive this thing with a misfire, the greater the chance of harming your catalytic converter, which is not cheap....

By the way, did you change the injector yourself? An why did you do it?