Beating my head against the wall. Sbc random missfire

[chevy2480]

Check your valve adj on that cylinder might have a valve not fully closeing i betting exhaust so it not getting a full burn if any.

 

[Stealth]

Intake has been port matched and the valves have been checked many times... Leak down is at 5% on that cylinder

 

[565bbchevy]

Why don't you post a video of it when it is misfiring if possible.

 

[Stealth]

Will do, I'm not sure how my phone will react to the noise but its worth a try

 

[Stealth]

I tried to capture the sound a few different ways and when I played it back it all sounds like the Same garbled mess.
I will see if I can get something with a better mic

 

[MD13ailey]

I totally missed the e85 thing. Are u sure your running the right heat range of spark plug? And im going to politely dissagree on the whole opening the gap and making more "heat" that may work fine on an 9:1 motor but in my expierience on bigger compression and msd systems the gap always gets closed up to keep it lit.

one could always email msd tech support at ask what they recommend for heat range and gap. To be sure.

What type of fuel system do u have?

 

[Stealth]

I have had this motor together for a couple years and it just started missing this season. I was thinking about contacting msd.. I have a Holley HP pump 2 inline filters that are clean and a QF Holley 850 double pumper

 

[MD13ailey]

Interesting that is would start now. Are all of your grounds good for the batter, body, and msd box? Its going to end up being something simple and stupid. Maybe cracked porcelain on a plug

 

[Stealth]

Good call on the grounds! I haven't checked those. I did change the plugs

 

[MD13ailey]

I was talking with my dad and he seemed to think u could have a bad valve guide. Running e85 it washes the oil off the valve stem as it come through the intake and out the exhaust ( obviously not as much on the exhaust side to to burnt fuel) but if the valve isnt sitting on the seat correctly u would be losing compression. pressurized the cylinder with air and listen to where its going. could do a compression test as well