So Ive been trying to track down this p0300 in my 97z for quite a while. Jus recently I installed a new long block, opti, plugs, wires, icm, coil, and have triple checked everything. Fuel pressure checks out great, and tonite i pulled the fuel rails loose to check for a leaking injector. None were leaking, so I then unplugged the icm and coil and had someone roll the engine over to ensure each injector was firing. But everytime he would go to roll it over it would try to start. This is happening while the engine is hot, and keep in mind everything is completely stock. I was thinking of trying a 160* thermostat and trying to find some colder heat range plugs. Any ideas yall have for helping me fix this misfire would be greatly appreciated.

 

Based on your description, above - You had the injectors/fuel rail out of the intake manifold looking for leaks, and to see if they were firing, and you had the ICM and coil unplugged, and when you turned the key to start, the engine tried to start..... without the injectors, and without the ignition? Is that correct?

 

there was no ignition, the coil and icm were unplugged. the fuel rail was lifted about 2 inches away from the intake manifold so fuel was still getting sprayed in.

 

and also the engine was at running temp

 

What heat range plugs are you running? try 6's

 

6's in which brand? I know some count the higher the number the hotter and vice versa. thanks

 

A simple scanner will tell you exactly which plug is misfiring. If you can't come up with one. Put it together and run it. Let it misfire for a while. Then pull the plugs when they cool. The plugs will tell you which one is misfiring.

You just replaced nearly the entire engine. You can't come off 150 to 200 bucks for a good scanner??????

I got news for you. An LT1 over 10 years old nearly lives on a scanner.

http://www.levineautoparts.com/autoxray-6000.html
Even cheaper is
http://www.levineautoparts.com/cp9180.html

And don't do a multiple posting for the same problem.
https://www.camaroz28.com/forums/sho...d.php?t=743758

 

I have a scanner but, No, I dont care to drop 300 on another one just to read misfire counts. The plugs all look identical everytime.(3rd set in 180 miles) the car runs really good, but throws a p0300 every 40 miles or so. What is the most preffered plug for a completely stock setup?

 

and also this scanner does not show misfire counts, I tried that one at autozone. It gives a lot of real time data but no misfire counts, total or individual cylinder.
http://www.levineautoparts.com/cp9180.html

 

[QUOTE=speedygonzales;6309315]
I got news for you. An LT1 over 10 years old nearly lives on a scanner.


QUOTE]

Man come on now....I wouldn't exactly call that an accurate statement

 

Was it tried in Generic mode? The first unit I pointed out can run in several modes. 2 of those three will show it also.

I make this statement based on scanning countless( can't recall how many) vehicles (using first a standard Snap-on scanner, then a color graphing scanner, then a Solus pro) while at the same time helping people on bulletin boards for years.

You're rolling your eyes based on what?

 

Do you actually have a mnisfire, or are you simply get a spurious P0300?