Alright I have the infamous po300 code and I read most of the threads and I cleaned the maf,throttle body, change plugs and wires and drop in a can of seafoam....The next step is the injectors....and I read on here talking about the cats going bad is there a way to tell if the cats are bad other than smell Its just killing me everytime I save up the money for my heads something else comes up and if I have to replace the cats Im buying a complete exhaust

 

Usually when the cats are bad enough to cause a misfire, the engine won't rev above 4k and will start to break up. You can check for a restriction in the exhaust with a vacuum gauge hooked up to a port on the intake. At idle the engine should have over 17 mmhg (that number will vary depending on if the cam is stock or not, larger cams with more overlap will have a lower number, while the stock cam will idle around 21 in park or neutral). When you rev the engine it should drop to 0, then quickly jump up to over 21 when you snap the throttle shut. If the gauge sticks or slowly rises after snapping the throttle shut, there is a restriction in the exhaust.

 

Ill see what I can do ,First Ill get some 8.1L injectors...

 

I just noticed the cam in your sig, sometimes larger cams can cause false misfire codes, although I'm assuming that Wheatley tuned for that and softened up the misfire monitors...

 

Well everything was fine until this winter...

 

Ill talk to my brother and ask him he has the same cam I drove his Avy and never seen a code or I might give Wheatley a call....

 

Yea, probably not cam/tuning related then...

 

Has the problem happened with more than one tank of gas? (trying to rule out bad gas...)

 

Yes I thought that was it to I was using Phillips66 I went to Shell and its tuned for 93 Oct...