350 Mercruiser MPI runs great in nuetral, NO POWER in gear

[Livinlarge]

Great site here, need some suggestions.

I have a 1999 350 Mercruiser MAG MPI 305 hp with a velvet drive on my 99 Sky Supreme.

It has run great but have had some issues latley. In nuetral I can rev the engine to 5000rpms with no issue and it sounds great, running strong.

However when its put into gear it can barley get up to 15mph and not over 1500rpm and sounds brutal (bogging down).

Here's whats been done so far:

-new plugs
-new coil
-new water/fuel seperator & checked fuel for water
-checked velvet drive for sign of burnt clutch, fluid look good
-checked rotar and cap

This problem started in the middle of the boating season, not after bringing it out of winterization.


Thanks!!

 

[Bondo]

Re: 350 Mercruiser MPI runs great in nuetral, NO POWER in gear

Ayuh,... Verify the fuel Pressure, 'n volume at the fuel rail....

The pump might be dying...

 

[Livinlarge]

Re: 350 Mercruiser MPI runs great in nuetral, NO POWER in gear

Replacing rotor, cap and ignition sensor tomorrow. Hopefully this works.

 

[franktrav]

Re: 350 Mercruiser MPI runs great in nuetral, NO POWER in gear

while yer in there[ignition]....hook up a timing light and make sure initial timing is correct AND the timing is advancing properly as you increase the rpms,,,,if its not advancing,yer not gunna get to high rpm under load
goodluck

 

[Livinlarge]

Re: 350 Mercruiser MPI runs great in nuetral, NO POWER in gear

Forgive my lack of knowledge. How would you go about checking the timing and ensuring its advancing properly? Also, if there is an advancing issue, would the replacement of the rotor, cap and ignition sensor solve the advancement problem?

 

[krisnowicki]

Re: 350 Mercruiser MPI runs great in nuetral, NO POWER in gear

Ayuh,... Verify the fuel Pressure, 'n volume at the fuel rail....

The pump might be dying...

this would be more likley

 

[Livinlarge]

Re: 350 Mercruiser MPI runs great in nuetral, NO POWER in gear

Here's where I'm at. Got a gauge on the fuel rail and got 33 psi, so not nearly enough. Went out and bought a new pump today and will be testing it in the water tonight.

I'm pretty sure it's the pump but I'll guess we'll find out soon enough.

Question: if the pressure in the fuel rail increases when the vacuum line is removed from the fuel pressure regulator, is this an indication the fuel pressure regulator is functioning properly?

Also checked fuel system from the tank to the pump and all seems good.

 

[Livinlarge]

Re: 350 Mercruiser MPI runs great in nuetral, NO POWER in gear

Fuel pump did not solve the problem, where do I go next? Suggestions please!!

 

[Livinlarge]

Re: 350 Mercruiser MPI runs great in nuetral, NO POWER in gear

OK I think Ive figured it out.

So psi in rail with new pump is just under 30psi. When i pinch off fuel return line in between fuel pressure regulator and fuel filter the psi jumps to 45-50psi. Is this fuel pressure regulator broken and need replacing? I think this might be it. Advice would be appreciated.

PS Comression in all eight 180-190

Thanks

 

[Cobalt293]

Re: 350 Mercruiser MPI runs great in nuetral, NO POWER in gear

Hi,

The fuel pressure is alright if you have pink mark on the fuel pressure regulator (later model Brown/Green mark has pressure)

The vaccum from manifold controls the fuel pressure regulator (at idle around 30psi at rail) when increased rpm = more vaccum it will increase the fuel pressure on rail (so if line removed - it more likely decrease), you should be able to see an increased pressure at rail when increasing rpm (around max 37psi).

So I don't fully understand your test with the return (did you plug it?) but from My point of view it sounds that you fuel pressure regulator is faulty (make sure you get a new one with pink mark).

Regards,

Mikael (sorry for bad english - Swede j

 

[Cobalt293]

Re: 350 Mercruiser MPI runs great in nuetral, NO POWER in gear

Hi,

The fuel pressure is alright if you have pink mark on the fuel pressure regulator (later model Brown/Green mark has pressure)

The vaccum from manifold controls the fuel pressure regulator (at idle around 30psi at rail) when increased rpm = more vaccum it will increase the fuel pressure on rail (so if line removed - it more likely decrease), you should be able to see an increased pressure at rail when increasing rpm (around max 37psi).

So I don't fully understand your test with the return (did you plug it?) but from My point of view it sounds that you fuel pressure regulator is faulty (make sure you get a new one with pink mark).

Regards,

Mikael (sorry for bad english - Swede j