Old harley
New member
I bought this boat about six months ago. It just doesn't want to go above 3400-3800 rpm. I've had 22p prop 19 p prop, 17 p prop, it planes in about 3 seconds with the 17 p prop but just struggles to get above 3400 rpm. I have verified compression, verified correct spark plug wires in correct firing order, had a fuel pressure gauge on the fuel rail and it is at 43psi all the time. I don't have a reader but using the forumn used a test light and have no codes. I followed procedures shorting the AB to time the boat and it is at 8 degrees and advances to 32 . But when I checked timing on the lake it starts to retard timing after 2000 rpm. When I hit 3200 rpm I am only 21 degrees advanced. I have unplugged the knock sensors no change. I replaced map and throttle sensors no change. I am wondering if it could be the ignition control module. Not sure how to test it. I get automotive parts cheap but the timing curve is different on the automotive ignition control module versus the mercruiser part from what I understand. Following another thread from someone with a similar problem they said clip the white wire in the group of four coming out of the distributor. This would prevent the ecm from retarding timing and go off of the ignition control module for timing. That didn't ,make a difference other than triggering an alarm. So what do I do now. Oh and new spark plugs.