I just changed all the plugs and plug wires on my '96 LT1 and now I am getting two SES codes. P0300 (misfire detected) and P0304 (misfire detected on cyclinder 4). To troubleshoot the problem I put the original plug and plugwire back on cyclinder 4 and I still get the same codes. I double checked my wiring on the rest of the cyclinders and all looks good. I should also note that I changed to NGK TR6 plugs with .035 gap (going to run a SC as soon as I get this problem figured out). What are the chances that the opti took a crap at the same time I changed plugs? Anyone else ever have this happen to them?

 

I had a bad misfire problem...traced it back to the plugs I had put in...after I changed a bunch of crap...showed up on #4 or something changed the plug...came back on #6...i had some autolite...put the factory delcos back in and it ran fine...these cars are super picky about plugs...unbelievable...was a PITA for like 2 months...

 

well I put the original plug back into cyclinder 4 and it still says I have a misfire on cyclinder 4, so now I suspect it's not an electrical problem, but rather a fuel problem. I did add an inline fuel pump just before I changed the plugs and wires so maybe I got some dirt in the line and it's plugging the injector. I took the fuel rail off tonight and I swapped #4 injector with the one on the other side of the rail. If the problem follows the injector I will no for sure it was dirt.

On a side note, when I was changing plugs I noticed that there was oil all over the starter and on the bottom of the oil pan so I guess my intake manifold seal is leaking again . So I'm going to pull the mainfold and fix the leak before I reinstall the fuel rail. The last time the mainfold seal was leaking it was still under warranty, so this will be my first time pulling the manifold. Wish me luck.

I was a little curious how the computer knows which cyclinder is misfiring. Anybody know how that works?

 

Misfires are detected by the crank sensor.