7.4 Mercruiser loosing rpm at wot

[milsomj]

I sea trialed a 28ft Carver crusier today, 1995. Runs one 7.4 merc with a Bravo1. 673hrs on the engine.
4800 rpm = 28knots When we pushed wot, the engine would surge between 4700 and 5000 fairly quickly. Some thought it was rev limiter, others, lack of fuel. Any thoughts?

Thanks,
Jim

 

[Bondo]

Re: 7.4 Mercruiser loosing rpm at wot

A Fuel Pressure Test,+ a Shop Tach,.........
Along with knowing Exactly what the Redline is would give you a Clue.........

 

[newport dave]

Re: 7.4 Mercruiser loosing rpm at wot

WOT range for that engine is 4200-4600. Merc ususally sets the rev limit 100RPM above the range max. That would be 4700. I think your bumping the limiter.

Dave

 

[Don S]

Re: 7.4 Mercruiser loosing rpm at wot

Do you have a Thunderbolt IV or Thunderbolt V ignition system? The TBV is the only one that has a rev limiter. The TBV system can be identified by having an ignition control module and a knock module mounted on the distributor. The TBIV system had either nothing or the ignition control module mounted on the distributor.
Could you actually hear and feel the engine surging, or was it noticed on the tach only.
While you call it a 7.4L, what does Mercruiser call it. Magnum 454 perhaps?
Is it carbed or fuel injected?
Do you by any chance have an engine serial number for your engine?