P0306 GMC -intermitant check engine light below 50kph or at idle why?

Question

replaced spark plugs swapped coils p0306 persists

Answer 1

P0306 Misfire number 6 cylinder

When a scan tool is used to detect a misfire , the ECM looks for variation of the crank sensor and with the help of the cam it can identify which cylinder is misfiring. but how it reports is another thing, Your misfire may not be number 6 cylinder, it may be number 2 that is causing the misfire and the ECM identified it as number 6 or the scan tool reports number 6. Inspect the number 2 cylinder sparkplug and swap the coil see if it moves. Chevy products for some reason does not report correctly when it comes to cylinder misfire identification. Also when there is a misfire that is confirmed from a particular cylinder and it misfire at idle and not at higher RPM this is a indication of a mechanical condition. A leak down test is the test that finds it. Here a GMC Envoy with a misfire number 6 cylinder , when tested number 6 cylinder that cylinder passed, A ignition analyzer was used and found nuber 2 cylinder needed more investigation, a leak down performed and the cylinder head removed, there was a hairline crack between the intake and exhaust valve, and it only coded a misfire only at idle .Keep your finger crossed and hope it just a ignition coil problem