Loss of power in rpm range

[Chap260sig]

Hey guys need a little help. I have a1998 mercruiser 7.4 liter 454 with a bravo 3. Engine serial number is 0L085239. I had an issue with a sensor making an alarm go off. I believe I have since fixed that issue, so I took the boat for a test drive and it wouldnt get up past 2700 rpms. It wouldn't get out of it's own way and I couldn't get it to plane off. In nuetral it will go up to 4000 rpms no problem as soon as it has a load 2700 is the max. It idles fine and drives at 5 mph fine and doesnt seem to be missing or sputtering. I don't even know where to start with this. I have put a new fuel pump in a couple years ago, i have the cool fuel system, also believe the regulator was replaced. I had some water in the fuel so put some dry gas in and replaced the water fuel separator yesterday. I also just replaced the starboard side manifold and riser. Doing the port side at end of season. Any help or ideas will be greatly appreciated.

 

[KJM]

does the prop turn freely with the drive in neutral? if not , maybe something wrong with the prop or prop shaft? replacing the manifold seems like a bit of a coincidence and i'm always suspicious of that, but if it idles good and revs good on hose, maybe not. people more knowlgeable (and better spellers) than me here (there are many) will no doubt have better ideas!

 

[Chap260sig]

Thank you and I haven't checked it on hose cause it's in the water. Long story short I put it in in May had an issue with an alarm going off wasn't sure what it was I thought it was the manifold and riser on the starboard side oveeheating so I replaced them. I didn't actually replace it until last week lol, got everything working again and I just got to taking it out for a ride yesterday and that's when I realized rhe issue with rrpm. When I put it in on the way from the boat ramp to my dock even with the alarm going off the boat ran great

 

[achris]

You have an MPI engine.

From the Merc serial number look up site....

0L085239 MERCRUISER 7.4L BRAVO MPI

So you need to get the computer software hooked up and see what's going on with the engine. It may be something the diagnostics can report, it may not be, but without that information, we're all just guessing in the dark....

You also haven't mentioned (in either thread, and I've closed the other one, https://forums.iboats.com/forum/eng...s-outdrives/10642761-diagnosing-audible-alarm), what fixed the alarm problem.

Chris........

 

[Chap260sig]

Sorry new to this forum thing lol. Thanx for the help. Sorry, It was a bad connection on the temp sensor I believe. I cleaned it and haven't had anymore alarm. Would water in the gas cause this problem by loss of power

 

[achris]

.... Would water in the gas cause this problem by loss of power

Err, yes...

With the temp sensor. Did you clean and re-plug it, or just unplug it? And here's where the software would be invaluable. It will give a live readout of the reported temp. It would tell us if this was causing the ECU to limit revs...

Chris........

 

[Chap260sig]

I cleaned it and replugged it. I also have a quick question. Do u think growth on the bottom of the boat and possibly outdrive could be a cause of this???. I know it sounds stupid but the boat ran great in May when I put it in aside from the alarm going off I didn't go near the boat all summer for various reasons and really in the last 2 weeks just got around to looking at it so it's sat for 3 months without moving. Just wondering

 

[achris]

It doesn't take much growth on the boat to slow it down. Friend put his in and it did 39 knots at 4800rpm. 7 weeks later it would only do 32 knots and barely made 4000rpm.

Chris....

 

[Chap260sig]

Ok so took the boat to shallow water today threw anchor got out and checked the out drive and alot of barnacles on props. I cleaned 99.9% of it off. I also checked the plug wires while I was out basically just making sure they were on good. On the way back I was able to get the boat up to 3700-3800 rpms but still felt like the engine was being held back from full power.