Logo
FULL SITE MENU

496 mag running problems after cruising 20-25'

V

vranas

New member
hello guys .I'm facing a problem and i do not know what else* i have to check...
I have an 496 mercruiser* engine on a cruisers 2870. The engine runs fine but after 20-25' at cruising speed is starting* "cutting"* rpms and if i continue the engine could shut down. These "cuttings" are looking like someone turning off the engine or cutting the fuel..If i retard the throttle for a while and then forward again the engine starting running well again but after 1-2'* the problem appears again.
When i checked the engine with the consult the engineer told me that he had several over temperature readings from the right exhaust elbow.The feeling touching the elbows justified that.
I've checked the sea water line to see if something is blocking the flow and i find old peaces from* impeller at the oil refrigerator .After that i checked the water refrigerator, the elbows i've change the impeller (the old one was intact) ,the thermostat valve and the elbow overheating detector .
I have checked all the fuel supply line from the tank to the engine filters etc ...but the problem is still remaining...any good idea??
 
Some areas, the "foot" indicator is used for "minutes"....I'd suspect a restriction in the fuel pickup/delivery side. Get a fuel pressure gauge and measure the pressure in the fuel rail at WOT, under load - measurements are better than inspections most days.

I would fix the cooling problem before the fuel problem...again, measurements are much cheaper than throwing parts at an issue
 
bondo said:
Ayuh,.... I'm wonderin' just how he's gettin' to crusin' speed, in 25 Feet, with a 28' boat...
Click to expand...

the engine is 496 mag 2001 model /electronic fuel ingection
the boat is cruisers yachts 2870 express
the spark plugs are 4 years old
i've checked for water in fuel was all o.k
i said that after 20-25 minutes (') at cruising speed...
The engineer told me that when the fail safe system of the engine detected the elbow overheat,* reduced rpm in order to prevent damage.Could spark plugs may cause problem like that?
thanks for the advice markomark *
 
Could spark plugs may cause problem like that?
Click to expand...
Four year old plugs will still work if they aren't fouled. It never hurts to pull the plugs and inspect them...the condition of the plugs can tell you alot about the combustion in the cylinders. They should be medium brown on the electrodes. Does it have a distributor? Remove it and look for carbon tracking.
 
Back
Top