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502 Dead Stalls above 2400 RPM - Need Help!

Old 06-11-2016, 11:33 PM
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Default 502 Dead Stalls above 2400 RPM - Need Help!

Hey guys, you've all come through in the past helping me on some issues, so here is my newest gremlin...

Took the boat out for the first time today for a sea trial. 1998 Baja 24 outlaw with a Gen 6 502 MPI. I just finished a full rebuild (down to the crank) of the motor and got everything together and in the boat a couple days ago. Splashed it today for a sea trial. Motor was running great. Oil pressure, temp, etc all read spot on and the motor sounded perfect. Issue started after leaving the long slow no wake out of the river...

After planing off, everything is smooth for about 30 seconds to a minute, then suddenly nothing. The motor instantly dies. Like I turned the key off. Sometimes it takes a bit of effort to get her started again (30 seconds after the kill). With a little coaxing on the throttle, it will fire back over and run (idle) fine. Plane off again - same thing 30 seconds to a min later. I tried to get a feel for where the issue starts, and it seems like after 2400 RPM is where I start having the issue. I can run it all day anywhere from idle up to about 2400 RPM. Anything above that, it just dies after the 30 or so seconds. Can anyone shed some light on this? I've done some research and I understand this year of motor is prone to some fuel issues. Prior to the rebuild, I never had an problem like this...

Thoughts?

Thanks all!!
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Old 06-12-2016, 12:34 AM
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Might want to check your fuel pressure first to assure it's not a fuel problem.
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Old 06-12-2016, 09:44 AM
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Originally Posted by picklenjim
Might want to check your fuel pressure first to assure it's not a fuel problem.
Where is the best place to install the gauge? Just plumb it in line somewhere?
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Old 06-12-2016, 09:13 PM
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Anyone? Anything?

Well I'll keep posting my process and hope that others chime in. I didn't have a chance to get a fuel pressure gauge on the motor today. Try to do that this week at some point. I tried doing the easy stuff today. Replaced fuel/water separator. Pulled the VST assembly apart and cleaned the screens. Took her out again and same problem. Just a cold kill at anything above 2400 RPM after about 30 seconds. Motored around the area at 1500 RPM for almost an hour without a single problem.

Anyone else????
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Old 06-12-2016, 10:07 PM
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their is a shrader valve in the front of the engine on the fuel rail,it is hard to find but it is their.have you checked for spark right after the engine dies?it may be a bad ignition coil.

Last edited by mike tkach; 06-12-2016 at 10:10 PM.
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Old 06-12-2016, 11:12 PM
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it would be wise to post your engine serial number and year model of the engine - so that some would understand how your app is set up. All 502's thru out the years were not set up the same as this holds true with all marine engines

Is this engine and set up a totally OEM stock app ???

A true 1998 year model should NOT have a VST set up it should be a cool fuel gen II set up.

I would recommend buying a OEM service manual per your app to show the testing and proper procedures to help fix it .
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Old 06-13-2016, 12:22 AM
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the example of what i am talking about NO VST for 1998 - VST went away after early 1996 your app is set up from 1993 to very early 1996 at the latest as you mentioned the VST and cleaning of it..

Gen II cool fuel Mercruiser - 1998 - 502 cid

http://www.marineengine.com/parts/me...nd-fuel-cooler

Last edited by BUP; 06-13-2016 at 12:29 AM.
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Old 06-13-2016, 08:04 AM
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Originally Posted by BUP
it would be wise to post your engine serial number and year model of the engine - so that some would understand how your app is set up. All 502's thru out the years were not set up the same as this holds true with all marine engines

Is this engine and set up a totally OEM stock app ???

A true 1998 year model should NOT have a VST set up it should be a cool fuel gen II set up.

I would recommend buying a OEM service manual per your app to show the testing and proper procedures to help fix it .
Engine Serial: K021642. I Mis-spoke above. The boat is a 1997 and I believe the motor is a 1996 model 502. It does have the VST system. I rebuilt the motor 100% stock. I do have the three OEM service manuals. I have not gotten a chance to page through them yet about this issue. Will take a look tonight.
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Old 06-13-2016, 08:57 AM
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There is a brass cap (looks like one off your truck's tire valve stem), In the front of your engine under the intake,on the fuel rail Remove it and there is a schrader valve under it that the fuel pressure gauge hooks up to.

Photo form google search for reference

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Old 06-13-2016, 09:02 AM
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Originally Posted by 92nsx
There is a brass cap (looks like one off your truck's tire valve stem), In the front of your engine under the intake,on the fuel rail Remove it and there is a schrader valve under it that the fuel pressure gauge hooks up to.

Photo form google search for reference

Thanks! I'll grab a gauge tonight.
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