502 Mag EFI performance issues
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502 Mag EFI performance issues

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    Default 502 Mag EFI performance issues

    I have a 98 502 mag efi that is exhibiting intermittent reduced power between 80 percent to WOT settings. Engine has about 500 hrs on, serviced regularly by same reputable shop and is Operated mostly in fresh water at lake havasu. When the engine starts to lose power it happens almost always when the air temps are above 95 degrees and after the engine has been run in these temps for at least 30 minutes. I think the common clue is higher air temps. When it happens it feels like it is not getting enough fuel. It generally happens when cruising and the throttle settings are pushed to at least 80 percent to WOT. Normal WOT throttle for my setup is 4900 to 5100. When down on power WOT RPM will drop to 4000 to 4400 RPM. The engine does not seem to miss, surge or run rough when this happens. The power loss feels like the engine just lost about 100 hp at the top end. The engine idles good and runs well at lower rpm and cruise rpm settings, and can be felt only 80 percent to WOT settings. Again the problem is intermittent.

    Both the inline and water separating fuel filters have been replaced. The plugs and plug wires have about 150 hrs on them since replacement. Bilge area gets god air flow both in and out. Spark arrestor is clean. Fuel pump is original. Fuel tank venting has been checked and is good. Problem happens with 87 or 91 octane gas, gas from many different stations, when the fuel tank is full or near empty. A compression and leakdown test on engine normal for hrs on engine. Both the seawater and engine circulation pump have been replaced, water flow checked and good, boat has been lake tested by local reputable shop with laptop diagnostics, no codes or problems found during 20 minute lake test.

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    Quote Originally Posted by Bucketlist View Post
    I have a 98 502 mag efi that is exhibiting intermittent reduced power between 80 percent to WOT settings. Engine has about 500 hrs on, serviced regularly by same reputable shop and is Operated mostly in fresh water at lake havasu. When the engine starts to lose power it happens almost always when the air temps are above 95 degrees and after the engine has been run in these temps for at least 30 minutes. I think the common clue is higher air temps. When it happens it feels like it is not getting enough fuel. It generally happens when cruising and the throttle settings are pushed to at least 80 percent to WOT. Normal WOT throttle for my setup is 4900 to 5100. When down on power WOT RPM will drop to 4000 to 4400 RPM. The engine does not seem to miss, surge or run rough when this happens. The power loss feels like the engine just lost about 100 hp at the top end. The engine idles good and runs well at lower rpm and cruise rpm settings, and can be felt only 80 percent to WOT settings. Again the problem is intermittent.

    Both the inline and water separating fuel filters have been replaced. The plugs and plug wires have about 150 hrs on them since replacement. Bilge area gets god air flow both in and out. Spark arrestor is clean. Fuel pump is original. Fuel tank venting has been checked and is good. Problem happens with 87 or 91 octane gas, gas from many different stations, when the fuel tank is full or near empty. A compression and leakdown test on engine normal for hrs on engine. Both the seawater and engine circulation pump have been replaced, water flow checked and good, boat has been lake tested by local reputable shop with laptop diagnostics, no codes or problems found during 20 minute lake test.
    Hang a pressure gauge on the fuel rail and see what your KOEO fuel pressure is. This would be the first thing a shop would do, short of scanning the ECM for codes. The fuel pump test will tell if your pump is still up to putting out the PSI needed at WOT (low vacuum, which is why you check at KOEO).
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Or Seth, either one Budweiser's Avatar
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    I'm not usually one for just spouting out a possible cause/solution without having a very strong inclination that I'm pointing in the right direction, but... I'm going to this time anyway.

    Only when air temps are over 95° and after the engine is good and hot... Gonna guess the ECU is retarding the timing due to a knock.

    And if it always takes at least 30 minutes to occur, why only perform "laptop diagnostics" for 20 minutes?

    Hope ya get her all figured out.

    -Seth-
    Last edited by Budweiser; 11-11-2012 at 01:31 AM.

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    this is all impossible. I have it on good authority that EFI is ALWAYS TURN KEY and trouble free.
    Has to be operator error.



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    Could the manifold absolute pressure sensor start to fail when the engine bay air temps start to rise and if so would the failing MAP sensor restrict adequate fuel delivery under heavy throttle demands ? no codes are showing in the ecm but if this sensor is only failing partially when the air temps start to rise would this explain my original desription of symptoms?

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    Quote Originally Posted by Bucketlist View Post
    Could the manifold absolute pressure sensor start to fail when the engine bay air temps start to rise and if so would the failing MAP sensor restrict adequate fuel delivery under heavy throttle demands ? no codes are showing in the ecm but if this sensor is only failing partially when the air temps start to rise would this explain my original desription of symptoms?
    Yes, MAPs can cause all sorts of problems, since the ECM relies on it heavily. The other thing is CTS (coolant temp sensor) as it tells the ECM to pull fuel back as temps rise. USUALLY if they go, they will give a COLD reading and the ECM stays very rich at full temp. I supposed it could be showing an overly HOT reading which would pull more fuel out. A scan should show that sensor out of spec, though.

    Regardless, carb or EFI, check for fuel pressure first. Since you said original fuel pump - at 500 hrs it has given a good life. Check it first.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    If the fuel pump is suspect, then what would cause the pump to exhibit inadequate fuel flow when the air temps and engine bay temps get hotter? The engine runs great during lower air temps and only starts to exhibit probelms when the temperatures get above 95 degrees. If the pump motor is worn at the end of its life at 500 hrs then as the engine bay temps get hotter is it logical that the pump motor becomes hotter from adjacent engine block heat and ambient air temps in the engine bay which cause the pump motor rpm to slow and produce a reduced inadequate fuel flow at WOT?

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    Quote Originally Posted by Bucketlist View Post
    If the fuel pump is suspect, then what would cause the pump to exhibit inadequate fuel flow when the air temps and engine bay temps get hotter? The engine runs great during lower air temps and only starts to exhibit probelms when the temperatures get above 95 degrees. If the pump motor is worn at the end of its life at 500 hrs then as the engine bay temps get hotter is it logical that the pump motor becomes hotter from adjacent engine block heat and ambient air temps in the engine bay which cause the pump motor rpm to slow and produce a reduced inadequate fuel flow at WOT?
    I may have NOTHING to do with it. It's just always wise to make sure your fuel supply is online. Start with the simple stuff.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Sounds like you need to find another shop. Either they tested the boat and couldn't figure out what it was doing when faulting, or they tested the boat for an insufficient amount of time and never got the fault to occur. Both scenarios are unacceptable if you ask me. Having an intermittent problem is different then having a problem that happens under very specific circumstances. From your description you have a problem that is easy to diagnose as it can regularly be duplicated, it just has very specific circumstances? Yes? Or is it an actual intermittent issue that in fact does not always occur even if you do all the things you described to make it happen?


    Andrew

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    Quote Originally Posted by gn7 View Post
    this is all impossible. I have it on good authority that EFI is ALWAYS TURN KEY and trouble free.
    Has to be operator error.
    well, it's damn sure impossible right now. fricken cold outside. won't see 95 for maybe 5 months. kind of hard to diagnose a problem when the conditions don't exist for the problem to occur...

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    ap67et10
    Sounds like you need to find another shop. Either they tested the boat and couldn't figure out what it was doing when faulting, or they tested the boat for an insufficient amount of time and never got the fault to occur. Both scenarios are unacceptable if you ask me. Having an intermittent problem is different then having a problem that happens under very specific circumstances. From your description you have a problem that is easy to diagnose as it can regularly be duplicated, it just has very specific circumstances? Yes? Or is it an actual intermittent issue that in fact does not always occur even if you do all the things you described to make it happen?


    Andrew
    The probelm is intermittent. Somtimes it happens and sometimes it doesnt. But when it happens it does so within the conditions i have described.

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    Or Seth, either one Budweiser's Avatar
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    Default My money is still on...

    Knock knock.
    Who's there?
    Timing retard.
    Timing retard who?
    Timing is getting retarded because of a knock knock.

    There are a handful of possible causes and I'm not as "in the know" as Andrew (ap67et10) or others here on the board... just my 2¢ based on your description of the problem.




    (Gonna contribute my current corny sense of humor to pain meds. Turning silly and don't much care for it. Oh well, you guys will just have to deal with it for now )
    Carry on...
    Last edited by Budweiser; 11-13-2012 at 03:41 PM.

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    Quote Originally Posted by Budweiser View Post
    Knock knock.
    Who's there?
    Timing retard.
    Timing retard who?
    Timing is getting retarded because of a knock knock.

    There are a handful of possible causes and I'm not as "in the know" as Andrew (ap67et10) or others here on the board... just my 2¢ based on your description of the problem.




    (Gonna contribute my current corny sense of humor to pain meds. Turning silly and don't much care for it. Oh well, you guys will just have to deal with it for now )
    Carry on...
    Very good possibility....but WHAT CAUSES knock? Lack of fuel, or excessive timing, or increased compression, OR - - something metallic came loose and is creaking and making false knock. This is all assuming the knock SENSOR itself is not at fault.

    IF IT IS knocking, WHY all of a sudden? What has changed - is the question.

    The basic rule is - it didn't do it when it was new. So, something has changed - or changes from time to time.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Or Seth, either one Budweiser's Avatar
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    Quote Originally Posted by Beer:30 View Post
    Very good possibility....but WHAT CAUSES knock? Lack of fuel, or excessive timing, or increased compression, OR - - something metallic came loose and is creaking and making false knock. This is all assuming the knock SENSOR itself is not at fault.

    IF IT IS knocking, WHY all of a sudden? What has changed - is the question.

    The basic rule is - it didn't do it when it was new. So, something has changed - or changes from time to time.
    Good points. What we don't know is how long the OP has owned the boat and how long has it had this issue. Is it, in fact, something that's come up all of a sudden or has it been going on for a while?

    Brand new should not have an issue, although if the intake temps are high enough... it's gonna knock.

    You're right, if it is a knock related issue, what's really of importance is the cause. The OP states there is good airflow in/out of the bilge area, still I'm curious what the actual air temp is under the hatch when the issue arises.

    The engine is at 500 hours, I'm sure the cause could be almost anything. Excessive carbon build up, a hiccup in one of the sensors, anything really...

    I absolutely HATE intermittent issues, you are robbed of any certainty that the issue is solved and just have to go on wondering if it's gonna happen again for whatever period of time satisfies you...

    anyway, just rambling...

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