LX Forums Forum banner
1 - 4 of 4 Posts

· Registered
Joined
·
208 Posts
Discussion Starter · #1 ·
Hello, I'm looking for some help in diagnosing my misfire issue. The last few months I have been getting a misfire on cylinder #7 (code P0307) only. It started out that If I started it cold there would be no misfire code until I stopped and then restarted the car. Shortly after that It would throw the code but I would not really notice that it would run any different. If I listen at the tail pipe I could defiantly hear an irregular thump thump tone in the exhaust on the #7 cylinder side. But this has grown steadily worse since then and now I actually have more of an aggressive thump thump and it throws the code all the time. I have run a compression test and I get 185lbs on #7 and the cylinder next to #7 . I have swapped out plugs, coil and injectors from the surrounding cylinders trying to get the code to move to a different cylinder but still throws the code for cylinder #7 . When driving it runs out smooth with no hesitation and seems not to have lost any power. Idle is a bit rougher then it was before this started but only a little. On deceleration it now pops quite a bit which it didn't do when this code first showed up. I have run a vacuum test on it and the needle is steady at 21 in. at idle showing no wavering like it has a misfire or valve problem. I also ran a bore scope inside cylinder #7 and things look good but I don't have a mirror attachment so I couldn't look at the valves….plan to get one though and do just that. Plug color in cylinder #7 is also good and the same color as the other plugs.

Next things I plan to do is pull the valve cover and inspect the springs, push rods and rockers. Oh and this motor has quite a few mods, 410 stroker, Kooks headers, Magnason supercharger (10lbs boost), ported heads, cam, nitrous, 87mm throttle body…etc. Looking for any suggestions or past experiences with a similar problem.

Thanks
 

· Registered
Joined
·
2 Posts
Hello, I'm looking for some help in diagnosing my misfire issue. The last few months I have been getting a misfire on cylinder #7 (code P0307) only. It started out that If I started it cold there would be no misfire code until I stopped and then restarted the car. Shortly after that It would throw the code but I would not really notice that it would run any different. If I listen at the tail pipe I could defiantly hear an irregular thump thump tone in the exhaust on the #7 cylinder side. But this has grown steadily worse since then and now I actually have more of an aggressive thump thump and it throws the code all the time. I have run a compression test and I get 185lbs on #7 and the cylinder next to #7 . I have swapped out plugs, coil and injectors from the surrounding cylinders trying to get the code to move to a different cylinder but still throws the code for cylinder #7 . When driving it runs out smooth with no hesitation and seems not to have lost any power. Idle is a bit rougher then it was before this started but only a little. On deceleration it now pops quite a bit which it didn't do when this code first showed up. I have run a vacuum test on it and the needle is steady at 21 in. at idle showing no wavering like it has a misfire or valve problem. I also ran a bore scope inside cylinder #7 and things look good but I don't have a mirror attachment so I couldn't look at the valves….plan to get one though and do just that. Plug color in cylinder #7 is also good and the same color as the other plugs. Next things I plan to do is pull the valve cover and inspect the springs, push rods and rockers. Oh and this motor has quite a few mods, 410 stroker, Kooks headers, Magnason supercharger (10lbs boost), ported heads, cam, nitrous, 87mm throttle body…etc. Looking for any suggestions or past experiences with a similar problem. Thanks
Did you figure out your misfire issue? I'm having the same exact problem but with cylinder #8. I have a fully built 428 stroker (gen3) with a Vortech supercharger (13lbs of boost) on E85
 
1 - 4 of 4 Posts
Top