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  1. #1

    Default 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    I have been trying to fix this problem for 3 months with the help of 2 mechanics. Nothing has worked so far. I'm hoping you guys can help steer us in a good direction.

    We launched our boat Memorial Day weekend and again in mid-June for several hours on the water with no problems. We launched again July 1. This time, I could not get the boat on plane. The engine RPM won't go above about 2800 to 3000 no matter how far I push the throttle. Engine sounds fine at idle and low RPM. Even sounds OK at 2800, it just won't go any higher. The engine only has 220 hours on it.


    Over the span of 3 months several things were checked and repaired/replaced.  In all cases we launched to test and there was no improvement in performance.


    The marine mechanic scanned the engine and there were no fault codes. He collected engine telemetry while on the water under load and the sensor data looked OK. There are no alarms and the computer is not reporting being in Guardian mode.


    Here is what we did:

    1. Replaced spark plugs (even though they looked fine)
    2. Replaced fuel filter, filter disk, and lower fuel pressure regulator (FPR had some black debris on screen).
    3. Checked fuel pressure at rail. It was OK (~42 psi at idle)
    4. Professionally cleaned fuel injectors (in case debris got in them).
    5. Replaced some rubber fuel lines in case they were internally degrading (gas tank to Cool Fuel module)
    6. Inspected gas in case it was contaminated (it was clear and uniform).
    7. Checked exhaust path shutters in Y-pipe (in case they broke/got stuck and were blocking exhaust) - they were OK.
    8. Checked manifold vacuum: it was low (12 in HG at idle)
    9. Performed compression test and leak down test. There was leakage, so heads were removed and resurfaced and valves and valve seats were ground down. At this point I should mention the engine overheated 2 years ago and the exhaust manifolds were replaced at that time. The mechanic believes the overheat warped the heads and caused the leaks.
    10. Replaced gaskets on heads, and intake manifold.
    11. Replaced the entire distributor (screw mount cracked)

    The head repair was quite expensive ($2500) and did not fix the problem. I'm getting pretty discouraged at this point. We are trying to consult with a Mercury rep to get some guidance. Not sure if we'll get any.


    My thoughts are starting to drift to the stern drive. Could the gearing be failing and holding back the engine RPM? The props are original and look fine (no damage).


    I can't even conceive of what else to check. Any guidance or advice is appreciated, especially if someone has seen this problem on this particular engine (5.0L MPI with PCM/ECM-555 computer)!
    Last edited by troman9; 09-30-2017 at 08:08 PM.

  2. #2
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    3. Checked fuel pressure at rail. It was OK (~42 psi at idle)

    While underway check the fuel rail pressure, you must maintain atleast 35-39 psi at the high power setting

    The head repair was quite expensive ($2500) and did not fix the problem

    You got taken to the cleaners there

    Sparkplug firing order checked. Do you have the std cap or the flat crab type?

  3. #3
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Quote Originally Posted by troman9 View Post
    I have been trying to fix this problem for 3 months with the help of 2 mechanics. Nothing has worked so far. I'm hoping you guys can help steer us in a good direction.

    We launched our boat Memorial Day weekend and again in mid-June for several hours on the water with no problems. We launched again July 1. This time, I could not get the boat on plane. The engine RPM won't go above about 2800 to 3000 no matter how far I push the throttle. Engine sounds fine at idle and low RPM. Even sounds OK at 2800, it just won't go any higher. The engine only has 220 hours on it.


    Over the span of 3 months several things were checked and repaired/replaced.  In all cases we launched to test and there was no improvement in performance.


    The marine mechanic scanned the engine and there were no fault codes. He collected engine telemetry while on the water under load and the sensor data looked OK. There are no alarms and the computer is not reporting being in Guardian mode.


    Here is what we did:

    1. Replaced spark plugs (even though they looked fine)
    2. Replaced fuel filter, filter disk, and lower fuel pressure regulator (FPR had some black debris on screen).
    3. Checked fuel pressure at rail. It was OK (~42 psi at idle)
    4. Professionally cleaned fuel injectors (in case debris got in them).
    5. Replaced some rubber fuel lines in case they were internally degrading (gas tank to Cool Fuel module)
    6. Inspected gas in case it was contaminated (it was clear and uniform).
    7. Checked exhaust path shutters in Y-pipe (in case they broke/got stuck and were blocking exhaust) - they were OK.
    8. Checked manifold vacuum: it was low (12 in HG at idle)
    9. Performed compression test and leak down test. There was leakage, so heads were removed and resurfaced and valves and valve seats were ground down. At this point I should mention the engine overheated 2 years ago and the exhaust manifolds were replaced at that time. The mechanic believes the overheat warped the heads and caused the leaks.
    10. Replaced gaskets on heads, and intake manifold.
    11. Replaced the entire distributor (screw mount cracked)

    The head repair was quite expensive ($2500) and did not fix the problem. I'm getting pretty discouraged at this point. We are trying to consult with a Mercury rep to get some guidance. Not sure if we'll get any.


    My thoughts are starting to drift to the stern drive. Could the gearing be failing and holding back the engine RPM? The props are original and look fine (no damage).


    I can't even conceive of what else to check. Any guidance or advice is appreciated, especially if someone has seen this problem on this particular engine (5.0L MPI with PCM/ECM-555 computer)!
    Where do you live?
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  4. #4

    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    I live in California, in the SF Bay Area. Not a lot of marine mechanics here. My go-to guy retired recently.

    The distributor cap is the flat type. I checked the spark plug wires and the order is correct.

    Underway, at 2800 RPM, the fuel pressure increased a bit to about 44 or 45 psi.

  5. #5
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Don't laugh, but have you pulled the boat to check the prop and if the bottom is clean?

    Jeff

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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Quote Originally Posted by troman9 View Post
    I live in California, in the SF Bay Area. Not a lot of marine mechanics here. My go-to guy retired recently.

    The distributor cap is the flat type. I checked the spark plug wires and the order is correct.

    Underway, at 2800 RPM, the fuel pressure increased a bit to about 44 or 45 psi.
    Do you have the serial number.

    Get a different Fuel pressure gauge and please check the pressure again. See if those number change with a different gauge.

    That pressure is high.
    Last edited by Docksidemarineservices; 10-01-2017 at 11:43 AM.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  7. #7
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    did you change the cap when the distributor was swapped?

  8. #8

    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Jeff, the boat is normally on a trailer so the prop and bottom are clean.

    Mako, the new distributor included a new cap.

    Chris, the serial number is OW365168. The fuel pressure is consistent with what I've seen before, at least at idle. Are you saying the fuel pressure under load should be lower? Would that explain this loss of engine power?

  9. #9
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Does it have a Gen2 or Gen3 Fuel cooler. Your serial number can have either.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  10. #10

    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    I'm pretty sure it's Gen 3. I've had problems with clogged FPRs over the years, and I've been told the Gen 3 in that year had internal paint overspray that wears off.

  11. #11
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    double check each one

  12. #12
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Fuel pressure on the rail should not drop below 35-38 psi at power

  13. #13
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Quote Originally Posted by troman9 View Post
    I'm pretty sure it's Gen 3. I've had problems with clogged FPRs over the years, and I've been told the Gen 3 in that year had internal paint overspray that wears off.
    What color is the cover on the fuel module? Black or grey?

    you should have around 38 psi at idle and around 42-43 at wide open throttle. If the pressure is too high you will never get the engine over 3000 RPM.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  14. #14

    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Chris, the cover is black. I'm 99.9% sure it's Gen 3. See image below.

    So if the fuel pressure is as I described (42 at idle, 44 at 2800 rpm under load), then this could limit the rpm to below 3000?

    The only thing left to replace is the Cool Fuel module itself. Is this what you are suggesting?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  15. #15
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    There is an updated lid if your module is in good condition. The black lid is painted. The new lid is anodized and grey in color. You can remove the regulator and check for paint. Simple to do.

    Do not purchase a new module, Get the fuel pressure down by cleaning out the regulator first and changing the fuel disk and filter in the module.

    On the back side of the module is a brass plug, it is the high pressure relief valve and is prone to sticking and will drive the fuel pressure up over 100 psi. Simple fix for this if needed.

    Yes, High fuel pressure on these systems will limit power.

    Now get another fuel pressure gauge and check the fuel pressure again.
    Last edited by Docksidemarineservices; 10-02-2017 at 12:15 AM.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  16. #16

    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    OK so I should add some more detail to the history I started with above. Item #2 on my list mentions that I replaced the fuel filter, disk and pressure regulator on the Cool Fuel module. This was all done prior to the loss of power (prior to July 1) because I noticed a higher than normal fuel burn rate on my Floscan gauge. This has been a chronic maintenance item for me. The filter or the pressure regulator gets clogged and the burn rate goes up, replace them and it goes back to normal. Never before have I had a loss of engine power.

    In May I replaced the filter first and the burn rate stayed high, so after the mid-June trip I pulled the FPR and noticed the screen was clogged with debris. I replaced it just before the July 1 launch where the power loss occurred. Bottom line: I don't expect replacing the filters and FPR again will help since they are brand new. I have wondered if some of the black debris went further downstream and clogged up anything else. That's why I had the injectors cleaned. But, could the pumps be affected?

    I'm assuming you're saying replace the black cover with anodized to prevent future paint clogging.. is the cover the only source of paint?

    The fuel pressure gauge I used is brand new, but I can borrow another one and get another reading at idle at least.

  17. #17
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Who and how did they clean the injectors? Did you clean the fuel rails and the high pressure fuel line too?

    The cover is the cause of the paint getting into the regulator. Pull the module out and change the lid. Check your fuel disk and see if it is still clean if you don't want to change it.

    When you have the module out you will see a brass plug on the back side. High pressure relief valve. Under the plug is a spring and a ball. the spring will cut groves in the plug and lock the ball down causing high fuel pressure. You will see what I am talking about when you take it apart.


    Until you get the fuel pressure back into spec all other diagnostics are a waste of time if needed.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  18. #18

    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    The fuel injectors were professionally cleaned by a service in Reno NV a couple of weeks ago. I don't know exactly what process they use (ultrasonic?). I cleaned the fuel rail with Carb cleaner. Nothing was done to the high pressure fuel line.

    Looks like I have some homework to do so I'll report back. I appreciate your advice on this. Regarding the relief valve, is that items 5 and 6 in the figure below? And I assume the cover is item 2?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Fuel Module exploded.jpg 
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  19. #19
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Quote Originally Posted by troman9 View Post
    The fuel injectors were professionally cleaned by a service in Reno NV a couple of weeks ago. I don't know exactly what process they use (ultrasonic?). I cleaned the fuel rail with Carb cleaner. Nothing was done to the high pressure fuel line.

    Looks like I have some homework to do so I'll report back. I appreciate your advice on this. Regarding the relief valve, is that items 5 and 6 in the figure below? And I assume the cover is item 2?
    Yes 5 and 6....a little sand paper will correct that issue.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  20. #20

    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    OK so I ran the engine today in my driveway and checked the fuel pressure using 2 different gauges and the manifold vacuum. The fuel pressure was 38 psi on one and 39-40 on the other. I went back and looked at my notes and the 42 psi I reported in my original post is incorrect, I had misremembered and it was more like 40 psi. I can't launch currently but I believe that I'd see about 43 to 44 psi like I did before at 2800 rpm under load.

    So... it seems like fuel pressure is OK , if I understand your guidance correctly. The manifold vacuum is 13 in HG, which I believe is still low. The valve/head work appears to have improved that by 1 in HG, but not within spec (if 15 to 21 is the right spec).

  21. #21
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Starting to wonder if the valve job has the rockers a bit too tight ,might try readjusting them to 1/2 turn from 0

  22. #22
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Showing results for low manifold vacuum causes
    Search instead for low manifold vac causes



    Search Results

    A vacuum reading at idle that is much lower than normal might indicate leakage through the intake manifold gaskets, manifold to carburetor gaskets, vacuum brake booster or the vacuum modulator. Low readings could also be caused by very late valve timing or worn piston rings.

  23. #23
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Each of these has a characteristic effect on vacuum and you have to judge their performance as compared to what is considered "normal". To do this, it's important to judge engine performance by the general location and action of the vacuum gauge needle, rather than just by a vacuum reading. What follows is a list of the kinds of gauge readings you may find.

    Normal Engine Operation
    At idling speed, an engine at sea level should show a steady vacuum reading between 14 in. and 22 in. Hg. A quick opening and closing of the throttle should cause the vacuum to drop below 5 in., then rebound to 23 in. or more.

    General Ignition Trouble or Sticking Valves
    With the engine at idle, the continued fluctuation of 1 to 2 inches may indicate an ignition problem. You should check things like spark-plug gap, primary ignition circuit, high-tension cables, distributor cap or ignition coil. Fluctuations of 3 to 4 inches may point to sticking valves.

    Intake System Leakage, Valve Timing or Low Compression
    A vacuum reading at idle that is much lower than normal might indicate leakage through the intake manifold gaskets, manifold to carburetor gaskets, vacuum brake booster or the vacuum modulator. Low readings could also be caused by very late valve timing or worn piston rings.

    Exhaust Back Pressure
    Starting with the engine at idle, slowly increase engine speed to 3,000 rpm. Engine vacuum should be equal to or higher than vacuum at curb idle. If vacuum decreases at higher rpm, an excessive amount of back pressure is probably present due to a restriction in the exhaust system.

    Cylinder Head Gasket Leakage
    With the engine at idle, the vacuum gauge pointer will drop sharply every time the leak occurs. The drop will be from the steady reading shown by the pointer to a reading of 10 in. to 12 in. Hg. or less. If the leak is between two cylinders, the drop will be much greater. You can determine the location of the leak by doing a compression test.
    Remember, engine problems can affect transmission performance. If you suspect an engine problem, connect a vacuum gauge to the intake manifold. Note the location and action of the vacuum gauge needle, and use that information to determine the engine problem. Correct the engine problem before doing extensive calibration work on the transmission.

  24. #24
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    8 to 14-Inch Reading

    A steady low reading between eight and 14 inches of mercury is usually indicative of incorrect valve timing.

  25. #25

    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Thanks for the info Bt Doctur. Assuming the gauge is reading correctly, this is a steady reading between 8 and 14. The only thing I can think of (FYI I'm not a mechanic) that would change the valve timing is the alignment between the cam and crank shaft, which are connected via a timing chain. Could one of the gears have slipped in the timing chain? Seems unlikely for such a low hours engine.

    How would I check for that?

  26. #26
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Incorrectly pre-loading the hyd lifter may do it. Another reason is #5 and #7 plug wires reversed. Have seen many run with no power and no other indication with those reversed.
    If the motor did perform correctly and now it dosent, something happened.
    With fresh heads correctly installed the vac should be closer to 17 .
    I would:
    Do another compression check with all the plugs removed and throttle body wide open.
    Physically trace each sparkplug wire from plug to cap.
    Physicall check each sparkplug tip for the correct gap.
    Get 2 long bolts, remove 2 manifold bolts and install 2 longer ones. remove remaining bolts and slide manifold back a bit to remove the valve covers. Check valve lash ,if you dont know how we can explain it .
    Check timing at idle and at 3500 rpm to see if it advances.

  27. #27
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Vac under the throttle plate or carb comes from the pistons sucking in the mix on the intake strokes and creating the vac in the intake manifold.Pistons dont suck= low vac and poor performance

  28. #28
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    About 69,100,000 results (0.87 seconds)




    Search Results

    Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere. Manifold vacuum is an effect of a piston's movement on the induction stroke and the choked flow through a throttle in the intake manifold of an engine.

    Manifold vacuum - Wikipedia


  29. #29
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited


  30. #30
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    Default Re: 2006 Mercruiser 5.0L MPI w Bravo III drive: Insufficient power to get boat on plane; RPM-limited

    Quote Originally Posted by troman9 View Post
    OK so I ran the engine today in my driveway and checked the fuel pressure using 2 different gauges and the manifold vacuum. The fuel pressure was 38 psi on one and 39-40 on the other. I went back and looked at my notes and the 42 psi I reported in my original post is incorrect, I had misremembered and it was more like 40 psi. I can't launch currently but I believe that I'd see about 43 to 44 psi like I did before at 2800 rpm under load.

    So... it seems like fuel pressure is OK , if I understand your guidance correctly. The manifold vacuum is 13 in HG, which I believe is still low. The valve/head work appears to have improved that by 1 in HG, but not within spec (if 15 to 21 is the right spec).
    Now, hook up the fuel pressure gauge and take the boat for a ride and see what the pressures are.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

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