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Chicago190
06-22-2008, 01:45 PM
So I had the engine replaced after it spun a bearing 3 weeks ago and am currently breaking it in. I have about 5 hours on it so far this weekend and have noticed 2 issues.

The first is that the engine never goes about 145 degrees, which is a problem I had last year and corrected with a new thermostat. When the dealership replaced the engine they also did a complete 100 hour service so they put in a new thermostat and I assume it is either sticking, defective, or a 143 degree T-stat.

The second problem is that when warmed up, the idle is not steady in neutral. It doesn't register on the tach, but I can hear the RPM going up and down probably 100 RPMs. I'm thinking a vacuum leak somewhere, but don't know obvious places to check on these motors. The boat also smells a little rich at idle.

Otherwise, the boat runs great.

JimN
06-22-2008, 01:58 PM
You'll never hear the RPM go down when there's a vacuum leak, only up. Make sure the MAP sensor tube is clear of fluids and has no cracks or leaks.



If you put a timing light on #1 plug wire, you should see the timing mark jump around. This is due to "spark stabilization" and because Americans like their motor to idle nice and smoothly. Once it's above idle, the IC module just advances/retards the timing as needed.

Don't try to guess at how much the RPM varies. If it's not showing up on the tach, it's not as drastic as you think. If the exhaust smells rich and it has a 143 degree thermostat, that is probably why. A little rich at idle is OK. If it runs rich at high RPM, then you need to look into it.

Chicago190
06-22-2008, 02:11 PM
It doesn't seem to be running rich above idle. Accelerates great and runs perfect at speed. Cruising at 1000-1500 RPMs and it doesn't seem to be smelling rich from the back of the boat. I won't be back up to the boat until the 4th of July weekend, so I'll bring a new thermostat with then.

As for the idle, I guess I was just surprised to hear the engine RPM varying because it had never done that before. I'll try to get a video of it this afternoon.

Chicago190
06-22-2008, 03:49 PM
Found a vacuum hose not seated 100% so I pushed it all the way on and now the boat seems to idle almost perfectly. I also stood on the platform for a few mins. and did not notice the exhaust smell I had before so maybe I was just imagining problems. Hopefully a new thermostat and the boat will be good as new again.

JimN
06-22-2008, 05:23 PM
Where was the vacuum hose- lower rear of the throttle body?

Chicago190
06-22-2008, 05:39 PM
Where was the vacuum hose- lower rear of the throttle body?

Exactly, on the starboard/drivers side.

JimN
06-22-2008, 06:00 PM
Heavy one or skinny? Heavy one would be the PCV and the skinny one goes to the MAP sensor, which I mentioned before and that one is the exception to what I said about a vacuum leak not lowering the RPM. A vacuum leak that only allows more air into the intake will always raise the RPM because it's like opening the throttle plate. When it changes the vacuum being read by the MAP sensor, the RPM will "hunt" because conflicting info is going to the ECM and it's trying to correct for it. Lower vacuum indicates that the throttle is more open, usually. If the TPS indicates <2%, the ECM is in idle mode and if the intake gets more air, the idle speed will increase, which causes the ECM to close the IAC until it's idling at 600RPM.

Chicago190
06-22-2008, 07:13 PM
It was not the PCV valve as I checked that hose first, so it must have been the MAF. I pushed the hose on all the way and revved the engine in neutral and the idle was steady so I think it solved the problem. Will report on the thermostat when I get back to the lake on July 3rd.

Thanks for the help as always Jim.

JimN
06-22-2008, 09:05 PM
If the hose that was loose is a bit sloppy, you can probably cut an inch off of the end, so you have a fresh piece to slide on.

Good to hear you got it.