Need Help with a Few Problems

[alparmer]

Picked up a 2007 Larson with twin Mercruiser 5.0 MPI Bravo III. Fired both engines up and went for a slow drive and within 20 minutes the port engine died. It will crank but it will not start. Made it back on one engine and when I got to the dock, I waited and it started normally again. I left it running and within 20 minutes it turned off again. Bottom line is that if I let it cool down a bit it will start again but around 20 minutes it dies.

Swapped IACs, fuel pump relays, took off top of carb, and everything looked as it should. Thinking it may be that the fuel tank wasn't breathing, I took off the fill cap, and no help. One thing to note is that the starboard engine sounds the alarm when key it turned to run, as it should, but there is not sound from the alarm on the port engine...the one I'm having problems with. My guess is that the buzzer is bad on that engine.

When I start the starboard, I hear the alarm, fuel pump relay and a very noticeable fuel pump fizz. On the port engine, no alarm, I do hear the fuel pump relay, and the fuel pump has the fizz but not as loud as the other engine. I really don't think its the fuel pump since I've only seen them go bad and not work again. It appears it's a sensor heating up.

I didn't have a whole lot of time and left it at the marina, which is 4 hours away. I should have checked for spark when it wouldn't run, but was so stressed it didn't cross my mind.

I'm guessing if no spark, it could be the hall sensor, ignition coil, or maybe even the magnets on the distributor itself. Am I on the right track? I purchase the techmate pro, but won't come in until later this week. I won't be able to drive down to the marina this week, so I will be forced to call a mechanic to get it fixed. I have to move the boat from southern FL to the central East cost this weekend.

BTW, all gauges show correct oil pressure, temperature, voltage, idle when running, and fuel tanks are full.

I would like to get the service manual but not sure which one I need for this particular model. I've narrowed it down to #24 or #31.

 

[achris]

Picked up a 2007 Larson with twin Mercruiser 5.0 MPI Bravo III. Fired both engines up and went for a slow drive and within 20 minutes the port engine died. It will crank but it will not start. Made it back on one engine and when I got to the dock, I waited and it started normally again. I left it running and within 20 minutes it turned off again. Bottom line is that if I let it cool down a bit it will start again but around 20 minutes it dies.

Swapped IACs, fuel pump relays, took off top of carb,

??? What?? 'took the top off the carb'. You said this was an MPI engine... No carbs on INJECTED engines. What did you take the top off?

and everything looked as it should. Thinking it may be that the fuel tank wasn't breathing, I took off the fill cap, and no help. One thing to note is that the starboard engine sounds the alarm when key it turned to run, as it should, but there is not sound from the alarm on the port engine...the one I'm having problems with. My guess is that the buzzer is bad on that engine.

So, first thing, troubleshoot the alarm problem. May be something as simple as the disconnected wire (maybe the previous owner was tired of the constant buzzing, and disconnecting it was the quickest way to shut it up. :facepalm

When I start the starboard, I hear the alarm, fuel pump relay and a very noticeable fuel pump fizz. On the port engine, no alarm, I do hear the fuel pump relay, and the fuel pump has the fizz but not as loud as the other engine. I really don't think its the fuel pump since I've only seen them go bad and not work again. It appears it's a sensor heating up.

Here is where you need the scantool, or better, the diagnostic software running on a laptop... Without that information, difficult to diagnose anything. While you're at it, put a pressure gauge on the fuel rail and make sure you're getting the right pressure. It could be the pressure regulator failing...

I didn't have a whole lot of time and left it at the marina, which is 4 hours away. I should have checked for spark when it wouldn't run, but was so stressed it didn't cross my mind.

I'm guessing if no spark, it could be the hall sensor, ignition coil,

of 1000 coils replaced each day, only about 3 are actually faulty.

or maybe even the magnets on the distributor itself.

No magnets in the distributor. All the timing calculations and coil firing is done within the ECU.

Am I on the right track? I purchase the techmate pro, but won't come in until later this week. I won't be able to drive down to the marina this week, so I will be forced to call a mechanic to get it fixed. I have to move the boat from southern FL to the central East cost this weekend.

BTW, all gauges show correct oil pressure, temperature, voltage, idle when running, and fuel tanks are full.

I would like to get the service manual but not sure which one I need for this particular model. I've narrowed it down to #24 or #31.

Engine manual - #31
Drive manual - #39
MPI manual - #36 (and #36 sup)
Exhaust system - #39
Fuel system - #40

Chris..........

 

[alparmer]

Thanks for the reply Chris. I meant, took off the flame arrestor on top of the carb. It is not a conventional carb but looks like one. I understand its a throttle body. Thats what I figured with the coil, never had one fail on me. Someone had mentioned weak magnets on the distributor shaft. I thought it made sense with the hall sensor, but not familiar with exactly what the hall sensor does. I would think something to do with position. good to know there are no magnets because that would mean replacing the entire distributor. Thanks for the service manual numbers, getting them all. We need to get the vessel off the marina by next weekend so pressed for time. I contacted the marinas mech and waiting to find out if he can get to it before the weekend. If not, I'm taking time off and try to tshoot it myself.

One thing the PO told me was that the engine bay got flooded due to a bilge pump failure. He said the mech went through it and changed all fluids and replaced both starters. Maybe the buzzer got soaked, or like you said, disconnected due to an annoying alarm which the PO didn't take care of.

 

[achris]

Thanks for the reply Chris. I meant, took off the flame arrestor on top of the carb. It is not a conventional carb but looks like one. I understand its a throttle body.

Throttle body, yes. Carb, most definitely not...

Thats what I figured with the coil, never had one fail on me. Someone had mentioned weak magnets on the distributor shaft. I thought it made sense with the hall sensor, but not familiar with exactly what the hall sensor does. I would think something to do with position. good to know there are no magnets because that would mean replacing the entire distributor.

No position sensing in the distributor. Actually, that 'distributor' is just a high voltage switch, and is often referred to as such, HVS... The crankshaft position is sensed by the CPS located low down on the starboard side of the engine front cover. That is all the ECU needs to determine when to fire spark. The HVS is just there to send it to the right spark plug.

Thanks for the service manual numbers, getting them all. We need to get the vessel off the marina by next weekend so pressed for time. I contacted the marinas mech and waiting to find out if he can get to it before the weekend. If not, I'm taking time off and try to tshoot it myself.

One thing the PO told me was that the engine bay got flooded due to a bilge pump failure.

Ummm, all bets are off! Flooded engine, soaked electrical system... Yeah, your problems are just starting... :facepalm:

He said the mech went through it and changed all fluids and replaced both starters.

Takes a lot more than changing the starter and oil to clean up a submerged engine... In my shop years ago, I had a cat that had gone down, twin 3L engines. We pulled both out and stripped them down to bare blocks. EVERYTHING got replaced, wiring harnesses, alternators, starters, steering pumps, fuel system got completely stripped and cleaned. Even after all that, the owner said as good a job as we did, it was never the same.

Maybe the buzzer got soaked, or like you said, disconnected due to an annoying alarm which the PO didn't take care of.

Good luck, I think you're going to need it... (Sorry for being the bearer of bad news)

Chris............

 

[alparmer]

Chris, the engine bay got up to the starter with water, not all the way. Nevertheless, I foresee future issues.

Spoke with the mechanic at the marina and he said he found the wire from the battery to the engine rubbing against the power steering pump. He sent pictures, but I wouldn't think that would cause the engine cutting off after about 20 minutes of run time....then cooling off, starting normally, and then quitting again after 20.

It looks like it's the negative cable. I've seen weirder things so maybe the chafed wire rubbing against the pump casing is somehow causing the issue. The mech said he had it running for 45 minutes without issues.

 

[achris]

If that's a negative cable, then unless there are ground problems elsewhere, it's not the problem.