Mag 350 mpi is this normal for fuel pressure?
By - chrispol1970
If you have a 3 bar regulator(I think you have a 3 bar regulator) it's a little low. Check it key on engine off, should be 42-43psi. Those I believe are vacuum actuated so at idle you'll have slightly lower pressure and at full load you'll have 42psi. Just revving it up unloaded won't tell you much, you need full flow rate and WOT.
Why are you investigating fuel pressure?
Ok will try at WOT.I can confirm 42psi with key on.
If you have 42psi key on engine off it's very unlikely to be a fuel pressure regulator issue. Under load is more important that WOT, but WOT under load is great, if you can get it.
What problems are you having that you're testing this? I don't think you have a fuel pressure issue.
Smell unburnt fuel from the exhaust sometimes. I have gone over every hose and have not found any leaks in the engine bay.
If you had high fuel pressure that could be plausible, but you don't have that issue.
I'd do a fuel pressure leak test. Key on engine off, get to 42psi. Then with the gauge on it, turn the key off and let it sit. Should easily hold 42 psi for 10 minutes. If it doesn't, you probably have a leaky injector.
Have you pulled the plugs and looked at them yet? Could be an ignition problem, when was the last time to did plugs, wires, cap, and rotor?
Next step would be getting an MEFI scan tool and checking to see that the water temp is being measured correctly, should be 160f when hot. If it's reading low it will over-fuel. Same tests should be done with the reading from the MAP and the GPS.
I changed all plugs rotor and cap this spring.
The plugs look good to me, one is a bit darker.
Tuesday will check WOT and leakdown
I agree, those plugs look decent to me.
Does it have a hard time on hot restart?
Good luck! Report back with what you find. I'm guessing it's either a leaky injector or a bad temp reading.
No hot/cold start issues 5k no problems, it's driving me nuts.
When do you smell fuel in the exhaust? Those engines are usually open loop, no O2 sensors, so they are rich to be safe.
What year is the boat/engine?
Engine is a 2002 on acceleration or coming off high throttle.
You need a water filled gauge. Any gauge attached to a pumped line will move around like crazy unless it is water filled
I don't know if this applies to you, but here goes anyway.
I have a Searay 310 Sundancer with twin 350 Mag MPIs. My engines have something called the Cool Fuel modules. I began having excess fuel consumption on the starboard side. I noticed because when fueling the boat, I was taking on double the fuel on the starboard side. I always fuel up full, so I knew there was excess consumption going on.
Finally got a mechanic who knew his shit, and he said there was excess fuel pressure and the root problem was the Cool Fuel module. Supposedly the first few years, Mercury provided a module painted on the inside. The fuel would corrode the paint, which would lodge in a screen just past fuel module and potentially clog injectors.
There was a tech note and even a recall on these modules. My mechanic contacted Mercury, and I got new modules and new injectors for both engines (I had to pay labor).
I have a fuel cooler, should of specified mag 350 mpi tow
2002 Mag 350 MPI Tow
Key on 42 psi within 10 seconds 30 psi then 20 psi in 1 minute.
Ok so I pressurized the system a few times and felt all around and it's the fuel cooler:(