Too Lean to be safe!!

[Daily Boater]

So I need some help please. I have a 2002 Mercruiser 5.0 MPI S/N-0M331599. The boat ran great up until the fall of last year when I noticed a fluctuation of power above 1300-1500 range that accompanied what seemed to be a misfire, popping or pre-detonation. I figured it was bad gas. It was the end of the season so I drained the tank down as far as I could and used an external tank to winterize after changing the water separator. This spring I decided to move to 100% zero Ethanol fuel 93% octane. I filled up. The problem from last fall was still present. Not only that but after a few minutes of running close to full throttle the engine shut down. Had a hard time keeping it running and after less than 2 min of running I got an alarm and the boat seemed to go into limp mode. I broke down and took it into the dealer where it was discovered Cyl. 5 & 7 were at 0 compression with cracks in the pistons and on Cly #1 at 120 PSI (the lowest still reading) and the piston appearing acid washed. Cyl #8 was 180 PSI. Didn't remove the head to inspect Cyl 2-8 but a borescope showed similar appearances to #1 in Cyl 4 & 6. So I R/R'd the long block and now I am breaking in a new Motor. Long story short, I fixed the problem but still have a cause. The motor is running Lean. I haven't even began to advance past 1800 RPM's in fear of repeating the damage. At R/R I also r/r'd Fuel Injectors, Cap/Rotor, Water pump and impeller. During troubleshooting yesterday, I returned the original Fuel Injectors back to the motor just to eliminate the new ones from the equation. No improvement. Spark plugs indicate a lean engine. Note all sparkplugs removed from the damaged engine looked fine with exception of 5 & 7 which the electrodes were melted. So I need help getting this problem under control before I damage another motor. Please help!! All indications, fluid levels appear good and no alarms have been present. New engine has aprox. 1 hr 40 min. first hour of break-in was performed on land with flush muff. The 40 min was on water on and off 5 different times. Fuel Pressure is 34-38 PSI, I also ran with a remote fresh fuel supply and a new water separator/fuel filter with no improvement.

 

[sandkicker]

Don't know about this specific engine control system, however, one common feature of all injected engines is the presence of an air flow(mass) sensor. This sensor determines the amount of fuel that gets injected. Also possible your engine control computer is defective. It sounds as if you are using the same engine control components on the new engine as the one you toasted. Usually the engine control computer will give you an error message if the air flow sensor is badly toasted, however not clear if it will give you a message if the air flow flap is stuck... By some chance, when the engine was winterized, is there a chance that the engine was "fogged" thru the air inlet???? Sometimes the fogging fluid damages the sensor. Usually in the manual, there is a test procedure for that sensor that make use of an ohmmeter.

 

[RicardoMarine]

So I need some help please. I have a 2002 Mercruiser 5.0 MPI S/N-0M331599. The boat ran great up until the fall of last year when I noticed a fluctuation of power above 1300-1500 range that accompanied what seemed to be a misfire, popping or pre-detonation.

I am not aware of any phenomena known as Pre-Detonation.
Detonation.... yes!
Pre-Ignition.... yes!

I figured it was bad gas. It was the end of the season so I drained the tank down as far as I could and used an external tank to winterize after changing the water separator. This spring I decided to move to 100% zero Ethanol fuel 93% octane. I filled up. The problem from last fall was still present. Not only that but after a few minutes of running close to full throttle the engine shut down. Had a hard time keeping it running and after less than 2 min of running I got an alarm and the boat seemed to go into limp mode. I broke down and took it into the dealer where it was discovered Cyl. 5 & 7 were at 0 compression with cracks in the pistons and on Cly #1 at 120 PSI (the lowest still reading) and the piston appearing acid washed. Cyl #8 was 180 PSI. Didn't remove the head to inspect Cyl 2-8 but a borescope showed similar appearances to #1 in Cyl 4 & 6. So I R/R'd the long block and now I am breaking in a new Engine. Long story short, I fixed the problem but still have a cause. The Engine is running Lean. I haven't even began to advance past 1800 RPM's in fear of repeating the damage. At R/R I also r/r'd Fuel Injectors, Cap/Rotor, Water pump and impeller. During troubleshooting yesterday, I returned the original Fuel Injectors back to the Engine just to eliminate the new ones from the equation. No improvement. Spark plugs indicate a lean engine. Note all sparkplugs removed from the damaged engine looked fine with exception of 5 & 7 which the electrodes were melted. So I need help getting this problem under control before I damage another Engine.
Yes..... it is extremely important that you do what-ever forensic work neccessary to find out what caused the problem in the first place!

Please help!! All indications, fluid levels appear good and no alarms have been present. New engine has aprox. 1 hr 40 min. first hour of break-in was performed on land with flush muff. The 40 min was on water on and off 5 different times. Fuel Pressure is 34-38 PSI, I also ran with a remote fresh fuel supply and a new water separator/fuel filter with no improvement.

Never...... repeat.... never attempt to break-in a fresh Engine or fresh re-build on the shop floor!!!!!
The Engine must be loaded in order to create the pressure behind the piston rings that is necessary for proper ring seating!

Don't know about this specific engine control system, however, one common feature of all injected engines is the presence of an air flow(mass) sensor. This sensor determines the amount of fuel that gets injected. Also possible your engine control computer is defective. It sounds as if you are using the same engine control components on the new engine as the one you toasted. Usually the engine control computer will give you an error message if the air flow sensor is badly toasted, however not clear if it will give you a message if the air flow flap is stuck... By some chance, when the engine was winterized, is there a chance that the engine was "fogged" thru the air inlet???? Sometimes the fogging fluid damages the sensor. Usually in the manual, there is a test procedure for that sensor that make use of an ohmmeter.

Bob makes some excellent points. Take heed........ in particular re; the fogging.
We DO NOT conventionally "fog" an MPI engine.


Good luck, and I do hope that you get this sorted out!


..

 

[makomark]

I'd suggest getting a scan tool and looking at the inputs to the computer (from the various sensors)....No codes infers no 'broke' sensors....but it also doesn't mean everything is fine....the typical example in the manuals is a biased ECT sensor.....this as well as many other sensors being 'off' (working but not accurate) will cause the ECU to pick the wrong point of the fuel delivery curve to use....and there's no efficient alternative to the scan tool....

 

[kghost]

I'd suggest getting a scan tool and looking at the inputs to the computer (from the various sensors)....No codes infers no 'broke' sensors....but it also doesn't mean everything is fine....the typical example in the manuals is a biased ECT sensor.....this as well as many other sensors being 'off' (working but not accurate) will cause the ECU to pick the wrong point of the fuel delivery curve to use....and there's no efficient alternative to the scan tool....

Great info

If he needed the dealer to diagnose the original failed issue he should have the dealer diagnose the lean condition also.

As with many of the EFI/MPI problems not often is there a magic bullet answer as there used to be with carburated engines.