Need Direction Diagnostic Guidance.....for a 4.3L Boat Engine.

[harringtondav]

Admins and Moderators, please forgive me. My boating forums replied with crickets when I posted this issue. Advanced EFI and ECM inputs are apparently a bit scary.
Short story. Engine is a 2021 Vovlo Penta 4.3 DI (GM industrial engine) 250 hp which ran like a beast until this year. Naturally aspirated.
After winterization I added 10 gals of fresh fuel to some leftover fuel which had been Stabil treated. At launch rough idle, poor rough acceleration. Intermittent alarm beeps. Low power. Sounds and feels like a 3.0L four, 1/2 power at best.
Pumped the tank, new fuel filter and 15 gals fresh gas. No improvement. WOT 4.4K rpm, 38 mph vs 5.5K and 52 mph. 25 more gallons of fresh fuel and another fuel filter. No joy.

Fuel xfer pump low pressure 10 psi vs 10-40 psi spec, high pressure 65 psi vs 55-65 psi spec. Direct injection rail pressure up to 2100 psi.
Recorded Diacom Diagnostic Engine, Fuel control monitor, O2 feedback, and Misfire monitor data.

No DTCs. Other than injector pulse width 4.7 ms max, and inconsistent closed loop status, any single input appears normal.
I can graph three inputs, and haven't found any abnormal interactions. The low injector pulse width looks like a key issue. Pretty sure full throttle pulse width should be 17-19 ms. ...don't know which inputs or conditions are holding it down.

So I'm looking for help comparing inputs that may indicate the issue. If you have are Diacom boaters you can send you the .rec files. Otherwise any other suggestions are appreciated.
TIA, Dave

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[RangerBill]

How is your air filter? Restricted exhaust?

 

[harringtondav]

How is your air filter? Restricted exhaust?

No air filters on most boats. Spark arresters instead. Medium/fine alum. mesh. I cleaned mine early on. Exhaust goes through water cooled manifolds and out the back of the boat mixed with water. No blockages.

 

[RangerBill]

Intermittent alarm beeps.

What do the alarm beeps indicate?

 

[airline tech]

My first thought - I do not have the Specs, but for a Fuel Injected Engine , 10 PSI Low Pressure is way too low.

So Fuel Pump or associated Fuel Pressure Regulator or (If installed) Anti-Siphon Valve or leaking fuel injectors - all of which can be associated with a low fuel pressure reading.

I have (Zero) experience on this engine - so just seeing a 10 PSI reading for a Fuel Injected engine caught my attention.

 

[harringtondav]

Two stage transfer pump. Low side for "internal" pressure (10-40 psi), 55-65 psi high side to feed the cam driven DI high pressure pump. Fuel rail pressures are 2100+ psi.

 

[harringtondav]

What do the alarm beeps indicate?

I don't know. That's what I'm trying to figure out.

 

[RangerBill]

I don't know. That's what I'm trying to figure out.

Does your boat or engine manual give any clues on the beeps?

I have read that low oil pressure, engine over temperature, low or high voltage can cause the alarm beeps. Some have had an issue with the manifold risers temperature sensors being bad.

 

[harringtondav]

I have all the paper manuals and diagnostic software. Sensor inputs are all normal when viewed individually. Injector pulse width is low and closed loop status is erratic.

 

[RangerBill]

I have all the paper manuals and diagnostic software. Sensor inputs are all normal when viewed individually. Injector pulse width is low and closed loop status is erratic.

The alarm beeps are indicating an issue and engine controls are limiting power in response. This would explain the injector pulse width that is limiting power output. If your diagnostic software is not indicating the cause of the alarm, it probably needs to go to the dealer for troubleshooting.

 

[RangerBill]

See this post on another forum concerning this engine. Scroll down to post #2.
https://www.garagejournal.com/forum/threads/no-user-serviceable-parts-inside.542903/

 

[harringtondav]

See this post on another forum concerning this engine. Scroll down to post #2.
https://www.garagejournal.com/forum/threads/no-user-serviceable-parts-inside.542903/

Thanks, good to know. My VP pump OEM replacement is about $1400 best price.
I'd need to set up a bench test after repair (if possible) to verify low/high pressures and output flow.

 

[got3fords]

Wasn't there recently another boat post where a new set of plugs cured it all?

 

[harringtondav]

Wasn't there recently another boat post where a new set of plugs cured it all?

That was me. New battery solved the shuddering and misfire counts. New plugs fixed the rest.
Diagnostic software showed low injector pulse width.....low fuel delivery. All other inputs and outputs were normal. Something was causing the ECM to hold back on the fuel. ....I got lucky with the spark plugs.

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