Mercruiser 350MAG MPI 5.7L with Bravo 1 cutting off when put in gear

[vzone675]

We have checked for all mechanical problems and have great compression; we replaced the old cool fuel module with a brand-new fuel pump module! New ignition coil and distributor. All 8 new spark plugs and band new bosch fuel injectors. The reason; we were fixing a long block piston ring that was incorrectly swapped so figured getting these replaced was a good idea.

The engine sounds great and runs on the hose/muff... We can even go up to 3500 rpm without it cutting out on the hose. But as soon as we dunk the boat into the water, it starts up but cuts out when we put it in the drive.

Giving it any amount of throttle, we notice that it struggles for a bit and eventually stalls. A couple of times we even hear it pop when we try to give it it some throttle

The diag cable does not show any obvious codes except that it has gone into guardian mode at 90% power when we try to apply throttle.

 

[Fun Times]

What year? Engine serial number is?

Kind of sounds like you ought try checking fuel pressure… also try cleaning the throttle body, throttle butterfly plate and Idle Air Control valve (IAC) and possibly the iac muffler, if applicable.

That or miss adjusted valves or tulip valves, etc..

Also try using a. Vacuum gauge tester to the engine.

 

[vzone675]

2006 S/N 0W619678

 

[Fun Times]

2006 S/N 0W619678

^ Gotcha, thanks... being an 06 engine model year, there doesn’t really seem to be to many possible known issues from that era for symptoms like that… mostly spark plug issues and distributor cap and rotor type issues.

Another thought would be to ensure the gm crankshaft reluctor ring is of the correct one/hasn't been messed with, etc. so that the crankshaft sensor is reading correctly 'being someone has been deep inside the engine.

Make sure the MAP sensor is working, and the O-ring to it is still good and maybe the TPS sensor too.... Doing it in the water indicates a load factor as revving to 3800 RPM before hitting the neutral gear rev limiter warning horn is easy to do as there is near zero load even at that RPM.

If all the above seems ok, then it sure sounds like it may be something internal especially with work done. Again, Vacuum gauge sounds needed honestly.

Lets us know good luck.

1998 Stern Drive 350 MAG [BRAVO MPI] [444206LTT] - Parts Lookup | Crowley Marine

View parts diagrams and shop online for 444206LTT : 1998 Stern Drive 350 MAG [BRAVO MPI]. Offering discount prices on OEM parts for over 50 years. FAST $4.95 shipping available.

www.crowleymarine.com

Just to clarify, the engine still goes into 90% each time you try to advance the throttle right now or is that an old code and not doing it anymore?
Is there any warning horns sounding off?

The diag cable does not show any obvious codes except that it has gone into guardian mode at 90% power when we try to apply throttle.

 

[dubs283]

Is time to check the drive

 

[vzone675]

^ Gotcha, thanks... being an 06 engine model year, there doesn’t really seem to be to many possible known issues from that era for symptoms like that… mostly spark plug issues and distributor cap and rotor type issues.

Another thought would be to ensure the gm crankshaft reluctor ring is of the correct one/hasn't been messed with, etc. so that the crankshaft sensor is reading correctly 'being someone has been deep inside the engine.

Make sure the MAP sensor is working, and the O-ring to it is still good and maybe the TPS sensor too.... Doing it in the water indicates a load factor as revving to 3800 RPM before hitting the neutral gear rev limiter warning horn is easy to do as there is near zero load even at that RPM.

If all the above seems ok, then it sure sounds like it may be something internal especially with work done. Again, Vacuum gauge sounds needed honestly.

Lets us know good luck.

1998 Stern Drive 350 MAG [BRAVO MPI] [444206LTT] - Parts Lookup | Crowley Marine

View parts diagrams and shop online for 444206LTT : 1998 Stern Drive 350 MAG [BRAVO MPI]. Offering discount prices on OEM parts for over 50 years. FAST $4.95 shipping available.

www.crowleymarine.com

Just to clarify, the engine still goes into 90% each time you try to advance the throttle right now or is that an old code and not doing it anymore?
Is there any warning horns sounding off?

^ Gotcha, thanks... being an 06 engine model year, there doesn’t really seem to be to many possible known issues from that era for symptoms like that… mostly spark plug issues and distributor cap and rotor type issues.

Another thought would be to ensure the gm crankshaft reluctor ring is of the correct one/hasn't been messed with, etc. so that the crankshaft sensor is reading correctly 'being someone has been deep inside the engine.

Make sure the MAP sensor is working, and the O-ring to it is still good and maybe the TPS sensor too.... Doing it in the water indicates a load factor as revving to 3800 RPM before hitting the neutral gear rev limiter warning horn is easy to do as there is near zero load even at that RPM.

If all the above seems ok, then it sure sounds like it may be something internal especially with work done. Again, Vacuum gauge sounds needed honestly.

Lets us know good luck.

1998 Stern Drive 350 MAG [BRAVO MPI] [444206LTT] - Parts Lookup | Crowley Marine

View parts diagrams and shop online for 444206LTT : 1998 Stern Drive 350 MAG [BRAVO MPI]. Offering discount prices on OEM parts for over 50 years. FAST $4.95 shipping available.

www.crowleymarine.com

Just to clarify, the engine still goes into 90% each time you try to advance the throttle right now or is that an old code and not doing it anymore?
Is there any warning horns sounding off?

Yea it was each time we advance the throttle on load (in the water - not the hose ). There is a horn but no code necessarily a long horn

 

[Cdn20valve]

have you checked fuel quality? If it runs good on muffs. and not in the water... check your fuel filter for water.

perhaps the angle of the boat when floating is allowing water to be sucked into the fuel pickup. and not when on the trailer.

how long was the boat sitting without being used?

 

[vzone675]

have you checked fuel quality? If it runs good on muffs. and not in the water... check your fuel filter for water.

perhaps the angle of the boat when floating is allowing water to be sucked into the fuel pickup. and not when on the trailer.

how long was the boat sitting without being used?

So we checked for vaccum leans non. Pumped out all old fuel and our new 91 octane fuel, replaced the fuel water filter and traced any obstructions from the tank to the fuel pump.
Engine compression on all 8 cylinders is 170+ the fuel pump reads between 36-38 consistent and at at 1500 rpm we are getting upwards 2.9GPH fuel flows rate from Diacon readings.

No water in the fuel. Brand new aftermarket Cool Fuel 3 module. Replaced the regulator on the fuel rail too.

 

[Cdn20valve]

So we checked for vaccum leans non. Pumped out all old fuel and our new 91 octane fuel, replaced the fuel water filter and traced any obstructions from the tank to the fuel pump.
Engine compression on all 8 cylinders is 170+ the fuel pump reads between 36-38 consistent and at at 1500 rpm we are getting upwards 2.9GPH fuel flows rate from Diacon readings.

No water in the fuel. Brand new aftermarket Cool Fuel 3 module. Replaced the regulator on the fuel rail too.

at this point, it only stalls when put in drive? is the drive seizing up? it can run all day at any rpm in the water. but as soon as you put in forward or reverse. it stalls out?

I would check the drive.