377MAG runs perfect, alarm still sounds

[skyman2112]

Cant seem to get the alarm to stay off no matter how many new parts i throw at this thing. Been to the dealer 7 times in 1 year already. Keep getting the same code, maximum number of misfires exceeded.. Replaced plugs, wires, cap, rotor, main engine fuse, new battery, oil sender, water pressure sender, drive lube monitor reservoir.
Sometimes the alarm goes off with 1 long continuous tone when i first start the engine but then does sound again. Sometimes is sounds a long 20 second beep while im driiving. Sometimes it beeps every minute and i have to get it reset. Cleaned and checked the crank trigger connector also and no change. Whats next? About to trade it in cause nobody can fix it. 2011 21ss crownline with 377mag catalyst motor.

 

[alldodge]

Been to the dealer 7 times in 1 year already

Need to find anther dealer, I don't think they know what their doing.

The new motors have to be scanned, and with your issues I would see if it can be scanned while running in the water.

 

[alldodge]

To add a tad more, I am unable to determine what is wrong without codes from a scanner, manual voltage readings. Since its erratic I might start with battery cables, both +/- and clean both ends to shinny metal, and make sure the wire under the insulation jacket is not corroded.

Solid beeps are
lube oil low (which you replaced)
Low oil pressure
Low water pressure (sensor on power steering cooler)
Engine coolant Temp overheat
Over speed (shift plat switch)
Port and/or Starboard Exhaust Manifold Overheat

 

[skyman2112]

Need to find anther dealer, I don't think they know what their doing.

The new motors have to be scanned, and with your issues I would see if it can be scanned while running in the water.

yeah i had it scanned and the code is maximum number of misfires exceeded. Which doesnt really tell you much. Definitely need to do it while its driving

 

[skyman2112]

To add a tad more, I am unable to determine what is wrong without codes from a scanner, manual voltage readings. Since its erratic I might start with battery cables, both +/- and clean both ends to shinny metal, and make sure the wire under the insulation jacket is not corroded.

Solid beeps are
lube oil low (which you replaced)
Low oil pressure
Low water pressure (sensor on power steering cooler)
Engine coolant Temp overheat
Over speed (shift plat switch)
Port and/or Starboard Exhaust Manifold Overheat

do you think a cam position sensor could cause the computer to think theres sporadic missfires? Thats the only other thing i can think of since it runs absolutely perfect. The code from the dealers scanner is 347 maximum number of misfires exceeded.

 

[alldodge]

I'm unable to find a code 347 for a misfire code. Finding there is 246 different codes and some more with digital controls. Unable to find the complete listing as yet. Wondering what scanner the dealer is using and wonder if their software is up to date.

My thought is the PCM may be the issue. If you can do without your boat for a week, would suggest sending it out to be tested. Could sean to Whipple or mefiburn

 

[skyman2112]

yeah im sorry i cant remember the exact code number it was 3XX, maybe 389? All i know is the rinda scanner description is maximum number of misfires reached. What do you think about the cam position sensor? Could it be a problem?

 

[alldodge]

The PCM is reading a misfire but there are none. If you were getting misfiring you would feel it. I don't know other then bad connection. The cam sensor just tells the injectors when to fire, so don't think that would be the issue. The crankshaft tells the distributor

Maybe see if you can get any advise from Rinda

 

[muc]

yeah im sorry i cant remember the exact code number it was 3XX, maybe 389? All i know is the rinda scanner description is maximum number of misfires reached. What do you think about the cam position sensor? Could it be a problem?

Yes it could be the cam sensor. But it could also be the propeller, key switch or just about anything in between them.

It it sounds like you have given a non MerCruiser dealer 7 try’s to fix this. Maybe it’s time to try a MerCruiser dealer? They will use a scan tool called CDS G3. While somebody who knows what their doing using Diacom can fix this problem, you haven’t found them yet.

You didn’t post a serial number so I can’t give you much advice on your problem, but I can give you some advice on misfires.

Basically a misfire occurs when the crankshaft speeds up or slows down too quickly. This can happen so fast that a human can’t detect it but the PCM can. So if you know what function the cam sensor preforms for the engine management system you can see that a bent prop is more likely to cause a misfire.

The boat most likely doesn’t need to be running to diagnose this but will need to be lake tested twice to confirm the correct repair.

Somebody who knows what they are doing can look at the scan tool and see what cylinders, at what RPM and a few other parameters the misfire is occurring and probably diagnose this fairly easily.

If you keep swapping parts, you have a much better chance of making things worse before they get better.

Also, one last thing I should tell you. If your misfires are letting unburnt fuel into the catalyst, they will burn out and the cost to repair/value of the boat will go up/down. And not in a good way.

 

[skyman2112]

Yes it could be the cam sensor. But it could also be the propeller, key switch or just about anything in between them.

It it sounds like you have given a non MerCruiser dealer 7 try’s to fix this. Maybe it’s time to try a MerCruiser dealer? They will use a scan tool called CDS G3. While somebody who knows what their doing using Diacom can fix this problem, you haven’t found them yet.

You didn’t post a serial number so I can’t give you much advice on your problem, but I can give you some advice on misfires.

Basically a misfire occurs when the crankshaft speeds up or slows down too quickly. This can happen so fast that a human can’t detect it but the PCM can. So if you know what function the cam sensor preforms for the engine management system you can see that a bent prop is more likely to cause a misfire.

The boat most likely doesn’t need to be running to diagnose this but will need to be lake tested twice to confirm the correct repair.

Somebody who knows what they are doing can look at the scan tool and see what cylinders, at what RPM and a few other parameters the misfire is occurring and probably diagnose this fairly easily.

If you keep swapping parts, you have a much better chance of making things worse before they get better.

Also, one last thing I should tell you. If your misfires are letting unburnt fuel into the catalyst, they will burn out and the cost to repair/value of the boat will go up/down. And not in a good way.

Thanks for the great information, i definitely need to find another dealer more familiar with mercruiser. In the mean time, i bought my own techmate pro scan tool and found out that not only am i getting the missfire code but also low water pressure code, which has been an ongoing problem with this boat for years.
A friend of mine said to check all the plugs to the computer and cam, crank sensor. I uplugged them all and they look fine so i sprayed contact cleaner on them and reinstalled. I also opened the pins on the crank sensor plug cause someone said that could not be making a good connection.
Since then i have not gotten a missfire code, only the low water pressure codee. My pump housing and impeller only have 30 hours on them since last year and the pressure sensor has been replaced 3 times in 300 hours. So im back to the drawing board on the water pressure issue. Hopefully the missfire alarm wont come back. Fingers crossed.

 

[chartersj]

Sounds like an issue I had with my 496....if yours has a brass gen 7 seawater pump you may be loosing water prime from a grooved impeller housing...mine would sound an alarm on the hose and the Impeller was in great shape. Installed a kit from aftermarket marine with wear plates and haven't heard the alarm since. Another option would be to replace the whole pump with a SS hardin marine one.

 

[alldodge]

Just to double check, you are using impeller part number 47-8M0104229 (Gen 7 pump) and not 47-59362T1 (Gen 2 pump)?

Is this open or closed cool?
Can you find a pressure gauge and connect to the block at one of the drains in the block?
Need one to read up to 30 psi, and mechanical oil pressure gauge would work

Would like to find out how the pump is doing

 

[muc]

Agree that confirming pressure with mechanical gauge is a good idea, but would recommend that you “T” into the system at the sensor because pressures can vary though out the engine.

there are a few causes of W.P. Sensor failure, but it depends on what engine you have

 

[skyman2112]

Agree that confirming pressure with mechanical gauge is a good idea, but would recommend that you “T” into the system at the sensor because pressures can vary though out the engine.

there are a few causes of W.P. Sensor failure, but it depends on what engine you have

I bought a rinda techmate pro and found out my pressure is low at all rpm. It never goes above 13psi.from 3000-5000 RPM. Seems like i dont have enough back pressure. The pump housing is new and so is the impeller. Attached is a picture or the housing and impeller that has 20 hours on it and not a scratch on it. I replaced the imipeller with a new one anyways. Im on my 3rd pressure sensor. I replaced the poppet valve spring and theres no change. I heard theres another check valve in a distribution housing on the port side. Maybe its stuck wide open and i cant get any back pressure.

 

[skyman2112]

Yes it could be the cam sensor. But it could also be the propeller, key switch or just about anything in between them.

It it sounds like you have given a non MerCruiser dealer 7 try’s to fix this. Maybe it’s time to try a MerCruiser dealer? They will use a scan tool called CDS G3. While somebody who knows what their doing using Diacom can fix this problem, you haven’t found them yet.

You didn’t post a serial number so I can’t give you much advice on your problem, but I can give you some advice on misfires.

Basically a misfire occurs when the crankshaft speeds up or slows down too quickly. This can happen so fast that a human can’t detect it but the PCM can. So if you know what function the cam sensor preforms for the engine management system you can see that a bent prop is more likely to cause a misfire.

The boat most likely doesn’t need to be running to diagnose this but will need to be lake tested twice to confirm the correct repair.

Somebody who knows what they are doing can look at the scan tool and see what cylinders, at what RPM and a few other parameters the misfire is occurring and probably diagnose this fairly easily.

If you keep swapping parts, you have a much better chance of making things worse before they get better.

Also, one last thing I should tell you. If your misfires are letting unburnt fuel into the catalyst, they will burn out and the cost to repair/value of the boat will go up/down. And not in a good way.

I unplugged all the connectors to the computer and cam sensor and sprayed aerospace contact cleaner/enhacer on it. Have not had another missfire code. The water pressure issue is my only problem now. Thanks for the great info!