PO300 Code

[Fred Clerici]

I have a 97 Eclipse 2 litre non turbo with manuel transmission. The current engine has almost 100,000 miles on it. My problem is that the check engine light is on and the code indicated is PO300 indicating a random misfire. The engine seems to be running smoothly and has excellent acceleration. I have taken the car to two independent shops and one dealership to solve this problem. So far the cam and crank sending units have been replaced, a replacement ECU has been installed along with factory plugs and wire set. The coil has been checked for proper operation and a full diagnostic has been performed all to no avail. After two driving intervals the light reappears with the same code message. Needless to say this has cost a lot of money and I cannot register the car. Is there anyone out there who can help me with this problem? I am desperate.

 

[PieEyedPiper]

More details.
I'm well-versed in 4g63 P0300, but not 420a. But I'd still be willing to help. It sounds like you've covered the basics, plugs, wires, coils, CAS and CPS.

Is there no physical manifestation while driving, just a code?

What events led up to this?

 

[E-Rock 87]

Missfires are fun! There is alot of factors that can cause a miss.

Is it usually wet when the code comes up?

A coil can test good(ohms and such) but still arc when under load. Water will help you see if it is arcing.

Had anything been replaced changed or modified recently?

 

[TheRock0720]

I had this same issue on my 420a. Turned out to be a bad coil pack. A few days went by after replacing it and the new one failed. Brought to my mechanic because I was fed up, he bought one and put it on and its been running strong 9 months later (knock on wood).

 

[david9291]

I had a similar problem with my Mazda 3, the coil measured fine but would miss fire periodically, a new coil fixed the problem.