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Mercruiser 5.0L won't rev out

kghost said:
OK there are only a couple of things left to try.

as I said earlier, ""A 50 % loss of power in my opinion is either a timing module issue or a coupler issue.""


Chris also mentioned swapping/replacing the pick up (mounted to inside bottom of distributor)

I would also suggest one other test, remove the tachometer wire from the ignition.

I would suspect it to be a GREY wire on the negative side of the coil. See if the tach may have something to do with it. A bad tach can also mess with the ignition.

Have you pulled the outdrive off and inspected the splines of the drive shaft?
Click to expand...


The pick up that Chris is referring to isn't that the ignition sensor with the 3 wires going to it.
if it is those readings came back at 3.1 Ohms. The manual says anything under .100 is faulty.

Tach wire is an easy one to do, only problem is its a trailer boat and every time I have to go to put it in the water it's about 1 1/2 hrs away.

No haven't pulled the drive off as yet, I'm not totally convinced that the coupler is faulty.
Theres no vibration, banging or clunking noises, the RPM isn't increasing and the boat basically staying stationery to warrant slippage. I could be wrong but aren't those some of the signs I should be getting if the coupler was gone ?
 
No

a slipping coupler does not always vibrate, clunk or bang. It simply spins around the splined shaft....

A bad coupler can and will drive a boat but as the load increases the coupler will slip/spin.

Most boat owners do not even know it is bad until it is completely wiped out and the motor overheats due to lack of water supply from the drive.

Again, this all started when you hit bottom and stopped/stalled the motor.

I am not there, I am only giving you my opinions from a million miles away......

I have never OHM'd out a pick up...........and yes it is the "sensor" this is more commonly called a pick up.. the rotor spins thru it and the make/break of the gaps acts like the old points ignitions opening and closing.

I personally have never seen a pick up cause this type of issue. Usually they work or they don't from my experience.

One other thought, you say it is running smooth, Are you sure all 8 cylinders are firing?

Does this ignition have a limp home mode? Like if it senses a over heat or other issue that causes the timing module program to go into limp mode?

I will look thru the manual closer for this to see if it exists as it usually is a mode with MPI/EFI not carbed motors.....

OK this is what I found,

MEAN-BEST-TIMING (MBT) SPARK ADVANCE
During light load cruising, the ignition module maintains optimal ignition timing by making
small spark advance adjustments. At a given rpm, the module will add a small amount of
advance and wait to see if there is an rpm change. If rpm increases, it will increase timing
more. The module will continue to advance timing until it no longer gets an increase in rpm.
Conversely, if it senses an rpm drop, it will start to retard some of the spark timing. Between
1200-4000 rpm the ignition module can add approximately 10-15 degrees of spark advance
to the base spark timing curve.
NOTE: The Audio Warning System is also connected into the ignition module circuit. If the
audio warning system becomes activated by the closing of one of the audio warning system
switches, the MBT feature is deactivated.

Not sure about this a the issue but it could be a factor............????
 
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Everything has been covered with the exception of a leakdown test. I know the compression is good, But.

As for the coupler being bad, you would have excess rpm's and no speed.

Here on Barnegat Bay in N.J. we have a lot of shallow water. I have seen props stripped to the hub, torn off drives, broken gimbals and too many busted skegs to count. I have stalled many boats in the shallows here with no ill affects. I just can't imagine running aground and just bending your prop causing this issue.

Dumb question, did you hook up a remote fuel tank and take it for a ride?


Time to pull the drive and take a look. Check the alignment.
 
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""As for the coupler being bad, you would have excess rpm's and no speed."""


Ah yes that is true........Long cold winter.......2 degrees above zero this morning........I have been thinking coupler issue in reverse.........me bad!!

Motor not reaching more than 1/2 normal operating speed or rpms would be fuel or ignition or wrong pitched prop or damaged hull or growth on hull.

Duh!!!

I wonder if the temp switch (a snap switch) closed on him but no alarm......

I out of possibilities..........
 
I was up in Saint-Michel-Des-Saints, Quebec sledding a couple of weeks ago. It was -35F. It's hard to think when that cold hits your forehead....LOL
 
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Had the motor running for around 15 mins on the muffs today.
it seemed to me that the Portside riser was a little bit warmer than the starboard side. I didn't have access to an infrared temperature gun to confirm this. Engine temperature on the gauge was a little under 175 Deg.
My original thought in my 1st post of it building up back pressure, feeling like it had a blockage in the exhaust still plays on my mind.
Even thou I had the manifolds off & risers and found nothing in the Y-pipe itself, can that half missing exhaust flapper be anywhere else in the exhaust system??
If I remove the drive is there any other place that the water flows out of besides the Y-piece that can cause a restriction?
 
the Portside riser was a little bit warmer than the starboard side.
Click to expand...
Normal if you can lay your hand on the exhaust 10 seconds or so and not get burned.
Even thou I had the manifolds off & risers and found nothing in the Y-pipe itself, can that half missing exhaust flapper be anywhere else in the exhaust system??
Click to expand...
No; unless it grew legs and crawled into the head. You have a multitude of expert advice to follow concerning total advance timing...have you checked it under load?
 
At the end of the Y pipe (inside transom assembly) where it meets the outside transome there are two exhaust ports at the 5 and 7 oclock positions.
Water and exhaust flows out of these in addition to thru the outdrive.

When you remove the outdrive the exhaust port thru the transom will be visable.

All mercruiser out drive power packages one side runs hotter than the other......sometimes ten to twenty degrees higher.......nature of the beast.
 
guyjg said:
Normal if you can lay your hand on the exhaust 10 seconds or so and not get burned. You have a multitude of expert advice to follow concerning total advance timing...have you checked it under load?
Click to expand...

Yes mate, did check T/A, it was approx 30 Degrees @ 3200Rpm & beyond.

kghost said:
At the end of the Y pipe (inside transom assembly) where it meets the outside transome there are two exhaust ports at the 5 and 7 oclock positions.
Water and exhaust flows out of these in addition to thru the outdrive.

When you remove the outdrive the exhaust port thru the transom will be visable.

All mercruiser out drive power packages one side runs hotter than the other......sometimes ten to twenty degrees higher.......nature of the beast.
Click to expand...

Doesn't the water enter the cooling system thru the raw pump on the Portside?
I would have thought if anything it would be cooler than the starboard side being the 1st point of entry!!
 
You have a alpha drive right?
Complete closed system, right?

Give us your serial number of the engine.

I looked at the water flow diagrams and it shows a on engine belt driven water impeller system.
Is this so?
 
kghost said:
You have a alpha drive right?
Complete closed system, right?

Give us your serial number of the engine.

I looked at the water flow diagrams and it shows a on engine belt driven water impeller system.
Is this so?
Click to expand...


Not a closed cooling system
Saerial No: OM673278

Cooling diagram of it would be nice thanks.
 
Do you have a on engine belt driven water impellor?

The manual shows this for all models...........but I will look again.

Note: if the belt driven water pump impellor is not there it is in the outdrive. This diagram is for both alpha and bravo. Bravo only has engine belt driven impellor.
 
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kghost said:
Do you have a on engine belt driven water impellor?

The manual shows this for all models...........but I will look again.

Note: if the belt driven water pump impellor is not there it is in the outdrive. This diagram is for both alpha and bravo. Bravo only has engine belt driven impellor.
Click to expand...

Thanks for the diagram.
It has a raw pump plus the belt driven pump on the engine.

I ended up emailing Mercruiser Tech support today, was quite surprised that someone contacted me within a couple hours.

Merc Tech said 2 things,
1: Replace the Distributor Ignition Sensor
2: Hook up an external fuel tank

Explained to him that I checked the anti siphon valve, ball was rattling freely and that I checked the resistance of the Ignition Sensor and it was within spec.

Didnt care, he said he has come across this issue many times before, both appear to be fine but it ended up being the problem.

For memory I think Chris said the same thing regarding hooking a remote fuel tank !!
 
Docksidemarineservices said:
There is an echo in here....LOL

"I can't hear you" lol..


Btw, How fast were you going when you ran aground stalling the engine?
Click to expand...


Chris I can't recall exactly, but I was either idling away in Neutral or just in gear to keep the boat steady whilst waiting for that imbecile for 30mins to get off the ramp so I could do my passenger drop off.
The boat was not powering away I was stationary at the time.
The ground under next was pretty soft sand, was surprised it wasn't churning any sand up before it stopped.
Usually you hear / feel the Skeg or prop doing this when your in shallow water.
 
Hi guys, finally solved My problem with engine not Revving out past 3200Rpm.
Hope this helps someone else out there with a similar experience.

A Wrong Prop recommendation by a Marine mechanic has cost me several hundreds of dollars and many lost hours chasing this problem.
Luckily, I'm pretty good on the tools and have a bit knowledge so I have saved a packet on man hours / Labour.

Summary:
Bayliner 245, 2004 Model
Engine: Mercruiser 5.0L Carby
G/box: Alpha One leg 1.62 Ratio
Prop: 15" Dia x 16" Pitch 4 Blade
Top speed: 60km @ 4700Rpm W.O.T

So, boat ran fine since purchasing it. Had been out on it approx 5 or 6 Times.
Problem started when I bottomed out on the sand which in turn stalled engine.
Engine stalled because I was in gear idling, revs where down / low so it killed the engine.
Bent 2 blades slightly which then caused a vibration.
After a while went to accelerate, boat wouldn't rev past 3200Rpm.

Step 1:
Purchased a new prop from a marine shop, mechanic recommended the Black Max 3 Blade 14 1/2" Dia x 19" Pitch.
Told me it would give me a couple more Kms Top speed & better fuel economy.
Later that week I put new prop on and went out to test it.
Boat still wouldn't rev past 3200Rpm with new prop.

Step 2:
Carried out the following repairs & checks as per my Post #30
The only additional things I done since that post was,
Check intank fuel pickup screen
Removed rear leg to check exhaust for 1/2 missing exhaust flapper.

Step 3:
Returned boat to water today with another prop which i borrowed off a mate, Quick Silver 3 Blade 15" Dia x17" Pitch
Boat instantly revved out to 3800Rpm W.O.T which was 600 Rpm more than last time out, then approx 10 seconds later it started getting on the plane with a top speed of 62km @ 4900Rpm.
Full tank of fuel and full tank of water with 2 people on board.
The engine purred along at that speed for about 5 mins and it felt great.

My Conclusion
Simply the 19" Pitch is not suited for a 5.0L Mercruiser in a boat like mine.
With that 19" pitch it just couldn't reach that optimum Rpm to get it any where near up and over that hill to start planing. That extra 600 Rpm more was what it needed to get it there.
My opinion of that pitch is that it may be more suited to a 5.7L with a bit more power.

Don't know how to post up a video of it ,,,,

Big thanks to all you guys that responded to my thread and helped me along the way with your expertise & Knowledge.
My next issue is, what prop should I put on as I'm intending to put a swim platform on which will add another 80 to 100kg.
 
GO BACK TO THE ORIGINAL................EASY ANSWER.......

You must reach spec on wide open throttle with prop selection.

If more off the line is needed then a smaller pitch which will give a higher rpms and maybe over spec., if more top end is wanted then a larger pitch but rpms may decrease as will off the line performance. There is no perfect prop for every situation just a best overall.


Most likley what you have is a underpowered boat for cost savings.....very common.

A 24 ft baot should have at minimum a 350 (5.7 ltr) ~ 300 hp and a Bravo II (this would make the boat perform like a 19 footer with a 350), but my opinion is it should be a 454 with a bravo I.

What you may need to do is contact the boat manufacturer and see what they reccommeded from the factory...if you have the owners manual it may contain that info
 
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