8.1's - Port requiring more throttle than stbd

Hey Ray

Hey Ray

Member
Jan 11, 2016
62
San Rafael, CA
Boat Info
1997 330 Express Cruiser
Engines
Twin Horizon 8.1
Last couple of times out my throttles have not delivered equal RPM's, need to give port more throttle. In the past I've always been able to get both engines in sync with one hand on the throttles and moving them evenly. Note: I do have Engine Sync gauge but not the capability to operate both engines with one throttle. There is an Engine Sync switch on the dash but it's connected to some aftermarket cockpit lights. Engines were scanned for codes very recently and nothing registered recently for port, although that was before I started noticing the issue. Thoughts?
 
Are you able to monitor fuel flow individually to confirm the port engine isn't just doing more work (throttle) than the other? Could be that there is nothing wrong with the engines and that you are losing traction in the starboard drive. Could compare engine rpm to speed individually to eliminate it as a possibility.
 
8.1s on a 1997? Repower, I assume?
Do you have smart craft gauges? If so, monitor the fuel flow on each engine. I just went through a bunch of this on a pair of MAG MPI 454s. Fuel starvation (or the beginnings of it) more often than not turn out to be the culprit. Mine issue(s) came down to the factory fuel line from the fuel water separator to the high pressure pump in the cool fuel 2 system being kinked, and collapsing on high demands, and probably a weak fuel pump. I just changed that too while I was in there. I also had a multitude of other things that I had to get out of the way before being able to isolate it to this issue.
If you want a nice long read, it may keep you from doing unnecessary things. Not trying to project my situation on yours, but other experiences can help you think about your particular situation.
http://clubsearay.com/index.php?thr...g-mpi-fall-off-after-2000-rpm-2450-max.92690/
 
Yes repowered Jan 2014, about 220 hours on engines, I've had the boat since 2015. Also had Cool Fuel Modules replaced in both engines two years ago under warranty. I'll give that thread above a read, thanks.
 
8.1s seem to go through plugs and wires on a regular basis. Mine gets both every 2-3 years.

Start off by swapping wire sets between engines. See if you can move the problem from one to the other. Could be a simple matter of weak spark on one or more cylinders.
 
With my 8.1's that's a sign that the plugs are due for replacement. They all look fine, but a couple of them are not firing consistently under load.
 
Not to over-simplify, but I noticed something similar to this late Sunday afternoon. Went over today to have a look, and one of the plug wires was loose. Hooked it back up and should be good to go.
 
If it’s not plugs or wires, then it is probably paint chips in a fuel injector or two. I’d start by pulling the plugs to see if there is one that look different then the rest.
 
While the 8.1s eat plugs and wires I am still amazed at how well they run even when a plugs need to be replaced.

-Kevin
 
Thanks for the tips. Had all the rails and injectors cleaned when I replaced the CF Module so I don't think it's that. Just changed the plugs last fall and haven't put many hours on them but I'll check the wires. And agreed, boat still runs great just a little harder to manage the throttles.
 
Maybe one of the cables stretched and needs adjustment.
 
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