2008 8.1 MerCruiser won't fire on cylinders 2/3/5/6. What could cause this. Other cylinders fire and engine will get up to about 3000 rpm. Its on a 340 Sea Ray with V-drives.
Hi, welcome to iboats... Are you getting any fault codes or warning horn sounds at all?
Has the engine been scanned by a marine scan tool?
You could have coil issues, fuse blown issues, plug wires going to ground creating a hidden sparks under valve cover components for a few example thoughts.....Or possibly have multiple internal PCM coil driver failures which if the case they can sometimes be repaired vs buying a new PCM as that is sort of a common issue too as noted in the following link, https://whipplesuperchargers.com/index.php?dispatch=products.view&product_id=73
With it being 2,3,5,6 I cannot see an individual splice in either the coil or injector harness
Suggest using the below wiring diagrams and match up and also ring out the connections. Being a 2008 the wiring below my not be exact as yours. If this is the case then note the wire differences.
The wire differences could be the clue that maybe one splice (like a ground) could be what the issue is
You didn’t post a serial number, so can’t be sure.
Check for spark and use a noid light to check the injectors.
Could be a batch fire PCM
might want to swap the bad motors PCM to the good motor. Don’t put the good motors PCM on the bad motor.
A vacuum leak will cause a similar problem. Try putting your thumbs over the crankcase hoses from the valve covers. There should be no vacuum. If there is then the intake manifold is drawing air from the underside from a crack or a leaking gasket.
