Mercruiser 5.0L won't rev out

Hi guys, first time posting on your forum searching for suggestions / answers to my problem.
I have read numerous thread about a problem similar / same as mine but no one has come back on and posted if they fixed / repaired the problem and what they found !!!

In brief: Bayliner 245 2004 model with 5.0L Carby,
Drive: Alpha 1 leg, Prop: 4 blade 15 x 16 Pitch
Hrs: 120

Recently purchased boat, had it out on the water 3 times (Salt water ) each time out was seeing @ W.O.T 60km @ 4700Rpm.
4th time out was in shallow water at the boat ramp prop bottomed out and engine stalled.
Started boat and went up river, noticed a slight vibration coming thru the floor and interference on the fish finder screen. Stopped the boat and inspected the prop, no surprise had slightly bent 2 blades.
Took off up river opened up the throttle to maximum throttle and the engine would not Rev past 3200 Rpm / Speed 21kms top speed. Oil pressure 40Psi, Temp gauge 170 deg.
No engine miss or back firing, engine was purring from idle right thru to 3200rpm
This thing would not get on the plane anymore.

Loaded boat up on the trailer, headed home, flushed the engine and whilst on the muffs it Revved out to 5000Rpm and bounced off the limiter under no load.

Repairs carried out:
Replaced prop, took boat out for another run, vibration had done but my W.O.T issue was still there.
Compression test: 175 - 185 Psi
Replaced Ignition coil and coil lead, rest of leads had between 4000 to 6000 ohms.
Removed exhaust manifolds & Risers to check for sand or blockages, all checked out clear.
Replaced exhaust flappers as one had half missing.
Checked Engine base timing 8 Deg with purple terminal shorted.
Swapped Carby with a mate who has the same model boat & no issues with his boat.
Checked fuel pressure 6 Psi

Took boat out for another run after doing the above repairs & checks and its exactly the same, problem is still there.

Any help would be appreciated.....

Two things come to mind,

If what you hit was hard enough to stall motor then you may have ruined the coupler where the out drive shaft goes into. (motor must come out to repair)

If the timing/ignition control module is bad it can "sometimes" cause a 50% reduction in rpms.

If your buddy has the same ignition maybe swap it out with yours...That would be the large black module attached to the distributor. There may be two piggy backed and the one on the outside I believe is the knock detect module.

Even though the boat moved I would remove the outdrive and inspect the drive shaft splines and see if there is any aluminum in the splines.

Kghost thanks for your input,
On my model the module appears to be mounted on the Portside Exhaust riser I don't have anything mounted on the distributor except the 2 wires that go to that module on the riser.
There are other checks that I have also performed like Carby filter, new spark plugs extra so I've pretty much covered all your basic checks.
It almost feels like there is an Exhaust blockage and its building up back pressure not allowing it to breath ang get the exhaust gases out. At the 3200Rpm if held there long enough it sort of smells like its running lean. If that module pulls timing out it would smell like that yeh ???

I would change the distributor cap and rotor, running aground seems to be just coincidental.

Chris, i understand what your saying about being con incidental but wouldn't i have an electrical miss if that was the case if rotor or cap were defective. Idles is exceptionally smooth on the water, doesn't back fire at any stage thru out the whole rev range up to that 3200 Rpm & no miss or surge?

Orssom said:

Chris, i understand what your saying about being con incidental but wouldn't i have an electrical miss if that was the case if rotor or cap were defective. Idles is exceptionally smooth on the water, doesn't back fire at any stage thru out the whole rev range up to that 3200 Rpm & no miss or surge?

Click to expand...

Nope. Just loss of RPM when the cap takes a .........

It almost feels like there is an Exhaust blockage and its building up back pressure not allowing it to breath

Click to expand...

Did you find the missing exhaust shutter?

guyjg said:

Did you find the missing exhaust shutter?

Click to expand...

No never found that half missing exhaust flap, the Y piece that leads from the risers out the transom was clear both sides. Inspected it with a torch & mirror plus put a wire rod down one side & it came up the other side & vice versa. Also fed the rod down & thru transom exhaust bellow nothing sign of the flapper.

You say it "smells" lean,

Well if the coupler is slipping it will not supply enogh water at high speeds/rpms thus get hot. Not the motor temp but the exhaust as there needs to be sufficient water flow thru the elbows at all times (raw water and closed cooling)

That said, even if the half flapper is stuck somewhere there still should be enough output flow to reach full speed I would think.

It would have to block off almost the entire opening at the base of the rams horns (Y pipe)........As you said it not doing that.


As Chris suggested, get your buddies distributor cap and swap it see if that helps....

As I said a typical issue seen when a timing module craps is 50% loss of power. Idle and running is perfectly fine but just no advance of timing.
Very similar to the older mechanical cyntrifical timing wieghts. If they were siezed or not spinning out you would loose ~ 50% power at high speeds. No getting on plane. You can check this while running in the water and a second person driving.

Give it full throttle and have your timing light hooked up and see where it goes.


Thunderbolt V Ignition

Spark Control Features
IDLE SPEED SPARK CONTROL
The ignition module controls ignition timing to maintain a calibrated idle speed by making
small spark advance adjustments. This feature is only active between 400-700 rpm.

ACCELERATION SPARK ADVANCE
When accelerating, the ignition module may add more spark advance to the Base Spark
Timing Curve. The amount of spark advance added depends on how fast rpm increases.
This feature is also active between 1200-4000 rpm. Within this range, the module can add
approximately 10 degrees of spark advance to the base spark timing curve.

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.

OVER-SPEED CONTROL
The ignition module will prevent the engine speed from exceeding a preset limit by stopping
the spark. The over-speed limit is set slightly higher than the top end of the rpm range. For
example, if the recommended range is 4600-5000 rpm, the over-speed limit would be set
at 5100 rpm. When rpm reaches this limit, spark is turned-off until engine rpm drops down
to a RESET rpm, which would be approximately 4750 rpm for this example. At this point,
spark comes back on.

KNOCK RETARD SPARK CONTROL
The knock control feature helps provide protection from harmful detonation. Knock control
is handled by the knock control module. This module receives a signal from a sensor that
is mounted on the engine block. The knock control module works in conjunction with the
ignition module to retard the timing if spark knock is present.

Based on the graph I attached your total timing when at wide open throttle should be around 32-35 degrees. A base of 10 degrees before top dead center and a timing module advance of~ 25 additional degrees.

Kghost your a champion, thanks for your knowledge and input, the same goes to you other guys who have contributed to this thread.

Correct me if I'm wrong:
A healthy motor should pull around 18 to 24 inches of vacuum.
So if i hooked up my vacuum gauge to the motor and it showed low vacuum say anywhere from 0 to 10 inches of vacuum this could possibly indicate late valve timing or possibly a vacuum leak at manifold.
Also whilst the timing light is hooked up, the timing mark at a steady RPM if it fluctuates back and forth
Is it fair to say that a it could be a result of a stretched timing chain.
This can cause power loss ?

Along with replacing cap & rotor button and swapping the module across with my mates one
Ill be also running these checks over the next day or two.

If you had a streached timing chain I believe you would experience a bad miss fire as the spark/cam timing would be off.

This would need to be checked in Base timing mode as the timing module and knock sensor may influence the results.

With a timing light connected as you rev the motor up to ~ 2000 rpms and then hold it steady the timing mark would be moving back and forth. also would see it bounce around under deceleration when going back to idle.
Dont think it is the timing chain. It would still get to speed but just not very cleanly. back fires would be expected.

Vacuum, Idle should be between 12 and 18 ish. Many varriables.... Max vacuum can only go to ~ 24 or so inches of HG in any situation such as this, very tough to reach more without a secondary vacuum source such as a aux pump. Rarely see vacuum that high on a motor...........Doubt it is a vacuum issue at all.........

Stick with ignition timing for now and as i suggested a possible bad coupler. Before water testing pull the drive off the boat and look at the drive shaft spline for aluminum biuld up. If ANY is present then this is your issue.

The only thing that should be on the splines is grease

Although I am not 100% sure if the knock sensor could affect this condition you are experiencing but if you run the motor with a timing light attached and tap the motor with a light hammer near the sensor (just forward of the starter typically where the block water drain is) the timing should move with each hammer tap as this will simulate a KNOCK condition. Run motor at 1500 rpms steady on the hose on the trailer. See if this happens


KNOCK SENSOR TESTING

IMPORTANT: The correct Knock Module and Sensor must be used. Using an incorrect
Knock Module or Sensor will result in unrecognized spark knock and engine
damage.
1. Start engine and warm it up to normal operating temperature.
2. Connect the positive (+) lead from the DVOM to the PUR/WHT timing terminal that
comes from the engine harness.
3. Connect the negative (–) lead from the DVOM to a good engine ground (–).
4. With the engine running, there should be 8-10 volts on this circuit. If voltage is not present,
ensure that there is 12 volts to the Knock Module (PUR wire Terminal “B”).
5. Advance the throttle to approximately 1500 rpm.
6. Disconnect the harness connector (BLU wire) from the Knock Sensor.
7. Connect the unpowered test light to a positive (+) 12 volt source.
8. To simulate an AC voltage, rapidly tap the Knock Sensor harness terminal with test light.
9. If Knock Module and wiring is functioning properly, you should see a voltage drop on the
DVOM. If a voltage drop is not seen, check the BLU wire from the sensor to the Knock
Module for a short or open circuit. If the circuit is functioning properly to this point, the
Knock Sensor may not be functioning.
10. Reconnect the Knock Sensor harness connector to the sensor.
11. While still watching the DVOM, lightly and rapidly tap on the engine block near the Knock
Sensor with a small hammer. If the Knock Sensor is functioning properly, you should see
the voltage decrease. If a voltage drop is not seen, the Knock Sensor is faulty.

Thought I was going to be bored this weekend

Will get back on with my findings in the next few days.

Cheers

Remember what you are trying to figure out and what happened before/when this occurred.

Everything was fine until you hit the boat ramp with a 24 ft heavy boat and caused the engine to stall. Think about this!! Not an easy thing to do, stall a running engine by stopping the prop from spinning!!!!



My opinion is that when this happened your problems started. Use this as a starting point for troubleshooting.

Could a ignition component fail cooincidentally? Yes But I am not so sure this is it. Again not sure, Anything is possible.

A 50 % loss of power in my opinioon is either a timing module issue or a coupler issue.

Could you have a fuel issue??? Maybe a shock could have dislodged the fuel pick up screen ( in the gas tank) but I doubt it. This would cause a intermittin fuel loss when running not a constant 50% loss of power. If a fuel issue is suspected the when under wide open throttle in the water if you were to pump the throtlle handle (like pumping a gas pedal in a car) this would squirt more fuel into the carb from the accelerator curcit and would give you a surge in power or slightly closing the choke a bit causing a rich condition.

dont go thinking the bow light may have something to do with the motor operation........if you know what I mean!!!!

Man I hate ordering boat parts over here in Australia. I have about 15 boat spare parts shops / repairers approx within a 20kms radius of where I live, do you think any of them stock a simply common distributor cap & rotor... Nope

www.ebasicpower.com ships worldwide

Finally my Distributor cap & Rotor came in, will pick up tomorrow from supplier.

In the meantime I carried out some fuel pump tests whilst I had the pump off.
The following test was performed on the workbench and not on the water with engine running.
Fuel flow came in at 3.4L per minute.
Fuel pressure test reading 10Psi.
Fuel pump bleed down 0 Psi within 30 Seconds.

I assume that the fuel pressure will drop to around 7 / 8 Psi once the engine is running with secondary jets discharging fuel.
Anyone know if the fuel flow of 3.4L P/M is within specs ??

I have to ask.....

Why are you testing the fuel pump?

You are not even sure you have a fuel problem...........

In most cases a 50% (clean 50%) loss of power is NOT related to fuel.

Fuel isses cause loss of top end, poor running, flodding, missing when running.



Anyway keep up up to date with findings......

Kghost...
Fuel never entered my mind being ever the problem. Thought I'd check the fuel pump whilst i had it out anyway.
The only reason I removed the pump was to get the part number off it and write it down in my part number notes.

Checked the Distributor cap it has no visible hair line cracks and the readings I got from spark plug lead post on the cap to the inner post on all 8 checked out good too, including the centre post.

I'll be replacing the cap & rotor tomorrow and taking it out on the water, I got a hold of my mates Knock Retard module so if it still plays up I,ll throw that on.

Remeber I said the timing control module NOT the knock module....The knock module will affect timing so (I think) if you were to disconnect the blue lead attached to the knock sensor that would take it out of the picture.

Here is a personal experience I had years ago.

I had a mercruiser 4 cyl (the infamous 470) It had a point igniton and mechanical fuel pump.

Boat started fine, ran great in neutral, revved up fine in neutral. Under load in the water it would not go above 2200-2800 rpms.


When I looked at the mechanical counter wieghts underneath the point plate in the distributor they were stuck and did not spin out (which is what advances the point cam).
Dissassembled and cleaned and lubricated and all was back to normal.

I understand you do NOT have a mechanical system but my point is I feel it is either a timing module issue or a partially spun hub.


Good luck........

kghost said:

You say it "smells" lean,

As I said a typical issue seen when a timing module craps is 50% loss of power. Idle and running is perfectly fine but just no advance of timing.
Very similar to the older mechanical cyntrifical timing wieghts. If they were siezed or not spinning out you would loose ~ 50% power at high speeds. No getting on plane. You can check this while running in the water and a second person driving.

Give it full throttle and have your timing light hooked up and see where it goes.


Thunderbolt V Ignition

Spark Control Features
IDLE SPEED SPARK CONTROL
The ignition module controls ignition timing to maintain a calibrated idle speed by making
small spark advance adjustments. This feature is only active between 400-700 rpm.

ACCELERATION SPARK ADVANCE
When accelerating, the ignition module may add more spark advance to the Base Spark
Timing Curve. The amount of spark advance added depends on how fast rpm increases.
This feature is also active between 1200-4000 rpm. Within this range, the module can add
approximately 10 degrees of spark advance to the base spark timing curve.

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.

OVER-SPEED CONTROL
The ignition module will prevent the engine speed from exceeding a preset limit by stopping
the spark. The over-speed limit is set slightly higher than the top end of the rpm range. For
example, if the recommended range is 4600-5000 rpm, the over-speed limit would be set
at 5100 rpm. When rpm reaches this limit, spark is turned-off until engine rpm drops down
to a RESET rpm, which would be approximately 4750 rpm for this example. At this point,
spark comes back on.

KNOCK RETARD SPARK CONTROL
The knock control feature helps provide protection from harmful detonation. Knock control
is handled by the knock control module. This module receives a signal from a sensor that
is mounted on the engine block. The knock control module works in conjunction with the
ignition module to retard the timing if spark knock is present.

Click to expand...

Question: Do all Thunder Bolts V systems fitted on Carburettor 5.0L or 5.7L models regardless of drive run the same Spark advance tables ??
Reason I ask is, I took the Ign Control module of my mates 5.7 today and his is marked 5.7L Bravo, whereas mine is a 5.0L with an Alpha leg. Also his unit has the knock module on it where mine doesn't run one.

I fitted it up tonight and it started fine, but haven't taken it out on the water as yet.
The only thing I can see happening is that it may advance earlier or a bit later than mine.

With the manuals I have it does not specify any difference between either drive combo for timing module. so yes they appear to be the same.

5.0 and 5.7 are the same ignition (again with what I have for manuals).


Also I believe all mercruiser thunderbolt V ignitions have a knock sensor........
I could be wrong, maybe someone else will know better than me.

So make sure you DONT have a knock sensor first. The sensor is located typically just forward of the starter where the block drain is. it is piggy backed on the drain hardware......

All TB V's do have knock mods. The knock mod will not take enough timing out to limit your RPMs that much. Put a timing light on and see what your total advance is @3000 rpm, it should be approaching 28 degrees.

If the module on the distributor has the plugs on top, chances are water has gotten inside and damaged it. There is an update for this.

Chris
I am a bit confused by his posts

If I read correctly he said his timing module was on the manifold. Maybe he has the wrong year listed in his original post?????

I thought most if not all TB V were attached to the distributor with the knock control piggy backed???

Also what "Plugs" are you referring to? Are you saying that some timing modules were mounted VERTICAL with the connections facing up?

kghost said:

Chris
I am a bit confused by his posts

If I read correctly he said his timing module was on the manifold. Maybe he has the wrong year listed in his original post?????

I thought most if not all TB V were attached to the distributor with the knock control piggy backed???

Also what "Plugs" are you referring to? Are you saying that some timing modules were mounted VERTICAL with the connections facing up?

Click to expand...

The modules can be stacked on the port riser.
Yes, On the early TB V's some of the modules were mounted with the plugs on the top side. Water enters and it's all over with. They have updates for this with a new harness. I would change the dist pick up also.

Yes I agree on the port side manifold mount BUT I thought that was on the early TB V set ups and with no knock sensor (early models it was not always included)......his is a 2004.....long after the TB V was in service.......so dist mounted and knock sensor.....

Something is not adding up......Maybe someone was in there messing around before he got the boat....

Docksidemarineservices said:

The modules can be stacked on the port riser.
Yes, On the early TB V's some of the modules were mounted with the plugs on the top side. Water enters and it's all over with. They have updates for this with a new harness. I would change the dist pick up also.

Click to expand...

kghost said:

Yes I agree on the port side manifold mount BUT I thought that was on the early TB V set ups and with no knock sensor (early models it was not always included)......his is a 2004.....long after the TB V was in service.......so dist mounted and knock sensor.....

Something is not adding up......Maybe someone was in there messing around before he got the boat....

Click to expand...

Guys here is a pic of my set up.
2004 model with no knock sensor on engine block, no knock harness & no knock module.
My distributor Ign sensor has 3 wires coming out of it. Nothing mounted on the distributor.
Power / Signal / Earth





Here is a pic of my mates 2005 model 5.7L Mercruiser ICM Module which I borrowed.
He has the knock retard module on his and both ICM & KR are both mounted on the Port side exhaust riser. Nothing else mounted on his distributor

Ok, here's the latest update.

Replaced the Dissy Cap & Rotor, swapped Ignition Control module with my mates one, took the boat out to the river today & guess what, THE Problem is still there.
Bellow is a snap shot of the instrument cluster and GPS showing the speed when the problem occurs.
Also hooked up an external digital tachometer up to verify the boat one is reading correctly.

Orssom said:

Ok, here's the latest update.

Replaced the Dissy Cap & Rotor, swapped Ignition Control module with my mates one, took the boat out to the river today & guess what, THE Problem is still there.
Bellow is a snap shot of the instrument cluster and GPS showing the speed when the problem occurs.
Also hooked up an external digital tachometer up to verify the boat one is reading correctly.

View attachment 8452

Click to expand...

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?

What I've done to date !!!

Parts that I've interchanged where off my mates boat which is a 2005 Model 5.7L Carby, Bravo 3 leg and is in perfect running order.....

Fuel System
* Removed & Inspected small fuel strainer located at inlet of Carburettor
* Removed mixture tamper plug ( Adjusted Rpm & Mixture screw as per manual with Purple / white wire shorted out )
* Screwed Mixture screw in until lightly seated & engine started running rough, screwed out mixture screw until engine started running rough. Sweet spot was approx 1 3/4 turns out.
* Replaced Fuel filter / water separator
* Bench flowed fuel pump 10 Psi / Delivery 3.4L per minute
* Swapped Carburettor with mates one
* Checked Throttle butterfly's on both Carburettors, at full throttle are wide open
* Currently on 4th tank of fuel since problem occurred

Ignition System
* Replaced Distributor cap & Rotor with new one. ( Old cap had good reading between posts, end up replacing it anyway )
* Replaced Spark plugs
* Replaced Ignition coil & coil lead ( Replaced old coil due to oil found in coil tower & inconsistent reading of coil lead )
* Tested Distributor Ignition sensor ( Returned readings of 3.1 Ohms )
* Tested Spark plug leads ( Reading where between 5000 to 8000 Ohms on the longest leads ) Did not replace
* Swapped Ignition Control Module with mates one ( Interesting enough the Only difference I found between my Alpha ICM & his Bravo ICM was, on the trailer with no load & on the water muffs it revved to approx 6000rpm whereas my Alpha ICM cuts spark out at approx 5100 Rpm )
* Checked Ignition Timing with Purple / White lead shorted out ( Base timing was 10 Degrees )
* Checked Spark advance whilst on the water ( At 3200rpm under load was reading approx 28 Degrees )

Engine Checks
* Compression tested cylinders ( Engine warm readings between 175 to 185 Psi )
* Removed Exhaust manifolds & Risers ( Both components were extremely clean )
* Replaced Manifold gaskets & Riser gaskets ( Riser gasket has restricted type )
* Replaced Exhaust Valve shutters ( Port side had 1/2 shutter missing )
* Replaced Engine thermostat 170 Deg ( Maintenance )

Propellor
* 15" Dia x 16" Pitch 4 blade when problem occurred
* Currently running 14 1/2" Dia x 19" Pitch 3 blade
* Swapped back to 15" Dia x 16" Pitch 4

As you can see in the Instrument picture above everything is running a normal Temps & Pressures

I'm at a lose with this issue