No Power over 3000 R.P.M on 7.4 M.P.I.

N

Nauti 97

Active Member
Oct 27, 2010
207
Lake Michigan
Boat Info
2000 380 Sundancer
2020 Highfield 340 dinghy with 25 HP Suzuki
Engines
7.4L Horizon engines
I have A 1997 370 Sundancer,
my problem is that when I took the boat out this weekend it was running fine, after being on the hook for several hrs. the boat started and ran fine until I throttled up, then the Starboard engine wouldnt go above 3000 RPM. when i got to the dock and put in neutral iI was able to rev it up fine. What is the issue? any thoughts?
Chuck
 
Crab pot? Check the shaft under the boat?
 
Is there anything wrapped around the prop or shaft? Crab pot line, plastic bag, lake grass? Crab pot line is what we see here a lot in the bay
 
Have not checked for something wrapped around the shaft yet.
that will happen this weekend. We don't have Lake MichiganLake Michigan
 
They're like boating in a mine field here! Also may wanna check the transmission fluid
 
Had the same issue on my 5.7l mag horizons. Changed out the plugs and everything was fixed. The only symptoms I had prior to it not revving one day was a rough idle when I fired it up this spring. The first few trips out I never had any issues. I am wondering if 3 seasons of fogging the motors during winterizing fouled it, as I wouldn't expect a fuel injected motor to gas foul plugs. I also read here that a "jingling/ringing" noise in your transmissions can signal 1-2 cylinders misfiring.

Troy
 
Water glide,
thanks for that info.
i changed the plugs in winter of 2011, only have about 100 hrs since.
i had no misfiring or rough running or rough idle. It just would not go above 3000 RPM. I have had no problems with it at all until this last weekend. I have put about 20 hrs on this yr already.
i am going to change out the fuel/water separator this weekend. Also going to check for a loose plug wire. I hope these small changes will solve it.
 
I had the same problem with my 1998 370DA several years ago. It ran fine up to about 3000 but would start to misfire if I tried to push it any further. Turned out to be a bad spark plug. Never would have guessed it because it ran so well up to 3k but that's what it was. I would assume that plug wires could cause the same problem also. Good luck, Mark
 
Thank you Mark,
i did not change wires when I changed plugs so I may need to do that.
my question is though, I could notice nothing different in the sound or the way the engine ran. Just no power above 3000. If it is misfiring will it not spit and sputter a little?
 
One of my 454s would not go above 2000 turned out to be fuel pump. I rarely run above 2000 that time I tried and the engine starved and stopped. I was in 5 Knot current at the time going against it. Not fun. Do not think you have fuel pump problem but if all else does not solve your problem check the pressure it puts out and see if it is correct.
 
I did not check the pressure at the fuel pump yet but I will.
the engine at 3000 did not quit or mis or spit and sputter still sounded fine, it just wouldn't rev up. What are the chances that it is Bad Gas? I had just added 75 gals the day before.
the gas is non ethanol 92 octane, the same as I always buy.
 
cjcray said:
Thank you Mark,
i did not change wires when I changed plugs so I may need to do that.
my question is though, I could notice nothing different in the sound or the way the engine ran. Just no power above 3000. If it is misfiring will it not spit and sputter a little?
Click to expand...

Just to clarify, when you say no power above 3000 I'm assuming you mean that it won't go beyond about 3000. When these fuel injected computer controlled engines start to misfire it's not as noticable as an old school engine because the fuel delivery and timing is adjusted on the fly to try to compensate so they still run fairly smooth sometimes depending on the problem.
 
Mark,
You hit it right on with the way it is running. I will look into the plugs and wires this week end.
I hope this is the problem, not a very hard (or expensive) repair.

Thank you very much!!
I really appreciate it!

Chuck
 
Mark,
Is there anyway to figure out which plug or wire is bad? Or am I best off to just replace all of them.
where can I purchase wires for Marine 7.4 M.P.I.?
 
It may be difficult to pinpoint which one it is since it only happens at high RPM when everything is being stressed. In my opinion it's not worth trying to fix just one. Replace all of the plugs and all of the wires. Chances are if you have a bad wire the rest of them are probably on their way out too. If the plugs are new you can try the wires first and then do the plugs if the problem doesn't go away. Not sure where to get parts in your area but make sure you have the serial number of one of your engines with you. Almost any thing I buy for my engines they want to know the serial number to make sure they can look up the right part.. There are a lot of subtle differences in years and models so the serial number is the best way to make sure you'll get the right stuff. I hope this will solve your problem. Mark
 
hello,
i am having similar problem, as 7.4 motor will stall after running boat for 15-20 minutes. i get boat up on plane, then after said time, it stalls out, like running out of gas.
i have replace rotor , cap, filters, added a water fuel separator. i thought the water fuel separator would solve this issue, but it did not.
i even loosen gas caps, to make sure it wasn't a vent issue. that didn't help either.
i think there's junk in tank??

any ideas welcome,

gordon
 
Last edited:
Geez, it must be the time for 7.4 issues! My starboard motor has run like this all season (only a couple trips actually). I could get to ~ 3200 rpms but then it would start shuddering & surging and the rpms would drop off to 1000 & felt like it would stall until I brought the throttle back, a minute or so of idling & I could attain the rpms again & it would do the same thing. The second time I went out it wouldn't even go over 2800 rpms & was worse. So my Mechanic just rebuilt the carb & changed filters etc. now I can get it over 4000 rpms initially but the other symptoms persist. Wtf is going on??


Sent from my iPhone using Tapatalk
Todd
 
Last edited:
Changed the fuel filter this weekend. That made no difference.
next weekend is plugs and wires since I didn't receive them in time this last week.
i did notice more of a vibration than normal and still will not rev above 3000 RPM.
so I am hoping plugs and wires will fix the issue.
Thanks
 
You must log in or register to reply here.

Forum statistics

Threads
113,161
Messages
1,427,505
Members
61,069
Latest member
Peter61
Back
Top