Re: 2001 Mercruiser350 MAG Horizon Low RPM @ WOT
I have a 2001 Mercruiser 350 Mag Horizon engine. From what I have read, a number of issues, the engine guardian system will retard the speed if a problem is sensed to avoid engine damage, to a bad injector, electrical etc.
You may want to be careful with what your reading as it may get confusing between all the different engine models out there now.
You're engine has the MEFI 3 ECM and it does not utilize the guardian system reducing engine power.
As far as I know the put a meter scan that showed no fault codes and checked the timing. No they did not check the fuel pressure. Serial no. is OL675956
The engine received a valve job last summer and was running okay.
Thanks for the serial number, it helps a lot.
Fuel pressure is important to know, Also you may want to do another cylinder compression test to ensure everything is still working correctly.
Do you know if each engine has its own fuel pickup tube coming from the fuel tank or does one pickup tube feed both engines? Reason I'm asking is because maybe you have one bad fuel anti syphon valve at the fuel tank restricting fuel flow.
Are you sure both props are in good condition?
Is the bottom of the boat clean?
Here is a list of possible causes of low WOT (Wide Open Throttle) rpm.
In no particular order
Engine Won't Reach Operating RPM. Check
1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.