Hi guys

Got a Volvo Penta GXI-F 5.7 here. It's got a misfire happening at idle. Not terribly violent, but it seems to misfire once every 10-30 seconds. Once the engine warms up it happens less, but still happens. Engine feels smooth and then gives a shake, you can feel it with hands on the exhaust manifolds, but it's actually more noticeable when sitting up in the bow. Any thoughts on the fix? Currently no scan tool so no codes, but from the looks of things a code doesn't get thrown with misfires any way like in a car. Thanks

edit: should add the misfire feels and sounds the same every time it happens. Unnoticeable at speed and I don’t feel any performance difference on plane.

Matt

spark plugs, wires every done?

Don't assume it's not throwing a code. I highly suggest getting the engine read, somehow, somewhere. If that isn't practical at this point in time, definitely check the cap and rotor; they tend to get the little carbon 'whiskers' which can cause what you describe.

Common causes of misfires in the 5.7 aka Chevy small block. This is more the gm core vs Volvo’s add ons

plugs- look for indicators of issues and when changed?, wires check for resistance and continuity (had one misfire once where the wire wore down and the spark raked to block causing a misfire), distributor (rusty, dusty, wore out).

next look at compression testing. You can end up having the beginning of a rebuild- valve seat leaks, rings leaking compression, cam shaft lobe wearing out.