Lost 200rpm on Port

[SeaAyeOwe]

So had a great day out today, but for some reason as I move my throttle levers above 2500 rpm I need more lever advance on my port to maintain synch. Until today both throttle levers were perfectly level at synch right through to wot. No pull one way or another. And both engine stay perfectly in synch when levers are level until I go above 2500 rpm and start to load the engines up.

If I place the levers level now the port is 200 rpm less that stbd. I did not push it to wot today to check if they both got up there. It is not the end of the world and other than this the boat is great - but something has changed.

I did have a lot of work done on my port engine recently when trying to hunt down a fault that turned out to be a distributor, I swapped lots of parts and had to check all my injector plugs.

Diver cleaned my hull and legs last week (no way to know if he did a less good job on my port but overall boat is great compared to two weeks ago).
Brand new plugs an hour ago,
Brand new DIST cap.
Fuel is same as before the problem appeared.
Cool fuel unit filters all changed out.

Any ideas guys?

 

[480ces]

Double check your plug wires. I'd bet you aren't getting ignition on once cylinder.

I had exactly the same issue on 8.1s

 

[knot-sure]

Check your fuel injectors they may be plugged with paint chips out of the fuel pump.

replaced my fuel pump it was clogged with salt buildup, finally after many dollars my marina contacted mer cruiser and they said to clean out fuel rails and send out the fuel injectors.
after losing the summer the boat is finally running right.

good luck

 

[fc3]

Do you really have a problem? Do both engines turn rated RPM at WOT? If so, it should be okay. If not, then you have issues to diagnose.

 

[SeaAyeOwe]

Do you really have a problem? Do both engines turn rated RPM at WOT? If so, it should be okay. If not, then you have issues to diagnose.

I honestly am not sure - I did not run them at wot. As I got to thinking about the issue on my return to my slip I thought about it but it was too late.

The only thing I do know for certain is that there was not an issue the outing before and both engines have always had an rpm synch when the levers were aligned perfectly. I will need to do some more testing when I get the chance and take it to wot to see if I can isolate it. I have a strong suspicion my port engine will now not run to wot.
Dave

 

[SeaAyeOwe]

OK - so yesterday I went to wot. Starboard engine maxed out at 4400, port at 4000.
Carrying full water tanks, 1/3 fuel 3 adults and a sail on th back with a 10ft zodiac on a sea wise davit.
The boat was bottom cleaned in the water with a diver but frankly is due a haul and paint and proper clean so I am not worried about the 4400.
I have physically chacked the plug leads and to my knowledge they all seemed pretty well connected. I will pull the boat soon for some significant maintenance this winter so will leave it until then but I am thinking a plug somewhere is not firing fully or in ave lost an injector pulse because of my pulling them apart when I was fault finding earlier.
I will get a diagnostic on it first to see what it tells me - if anything.