ISM MISFIRE @ 1500 RPM

[Rawze]

(04-21-2021 )tree98 Wrote:  ... Maybe pressure test the head to rule out a valve/head problem.

Maybe back off all the rockers/valves so that the valves are all closed and pressurize the intake manifold to about 20 psi? .... check for compression leaks at the valves?.. and then do the exhaust manifold side?

I have found many mysterious combustion and fuel mileage problems by simply doing this, finding out that the valve seats are worn out/leaky in older engines or engines with used head on them.