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thanks
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I have an EFI 502 and all the plugs look fouled except the #8 its clean and full of fuel...... any suggestions?
thanks
Don't run the boat and have the fuel system checked.
A guy I know with a older 502 had the same problem, don't remember the name of the part but it had a float and a needle valve and would let extra fuel go into #8.
Well it stuck and put in so much fuel it got in the oil and failed the bearings, cost was a total rebuild.
Sure some one hear knows the name of the part to check.
You are so right Donzi Dude! Went thru this last year at this time with my 94genv 502 EFI. Get your bank roll ready for high dollar rubber o-rings.Around here nobody has anything on hand.I went to Jegs and bought an EFI return, ran bypass back in tank. I know, not CG approved. It was short term fix till I could round up needed needle and seat and oring for top cap. The oring will grow while not put on cap,crazy but it has a mind of its own. When this goes bad at wot it is a mess,drain oil 2or 3 times etc. Its hard to hide a trail of gas running you down the lake. I hope this helps.
there are a whole raft of things that will cause the injection to be full rich and shotgunning the repair is the wrong way to approach it. if your intent is to try to fix it yourself, you will need a the factory workshop manual and a voltmeter and some patience. a scanner would be a great help.
in the meantime there are several simple and easy things to check first.
put a fuel pressure gage on it... is the pressure correct ?
the water temp needs to be at least 165 degrees. any less and it will do what yours is doing.
the water temp sending unit ( the ecu sensor... not the gage sensor) needs to work and be hooked up. if it has been removed and siliconed back in or a wire is broken on this or any other sensor the ecu will make it go full rich.
and this is all presuming the ecu hasn't had a " magic flash" by someone and is now scrap...
and thats what you are talking about here. if you are saying that all the plugs are fouled, don't get caught up in this # 8 cyl red herring. if all the plugs are fouled then the ecu thinks the water is ice cold or the air temp is off scale or the map is bad or any nmber of other wrong sensor inputs. if the thermostat is stuck open and the motor never warms up it will do this...
do the diagnostics in the manner that the manual describes and you will find your issue in the quickest and cheapest manner. if you just start throwing parts at it without doing the fundementals , all it will do is cost you money and not run when you are done anyway...
and i am talking about the actual mercuiser manual... not some aftermarket garbage. if you are going to own an efi boat you need both the manual and a scanner like you need need air to breath.
Last edited by stevesxm; 08-11-2012 at 12:06 PM.
Platinum Member
Some very sage advice Steve but in this case the OP has a early Mefi sytem and what happens is it has a mechanical pump that fills a sorta resevoir (VST tank) on back of the motor that feeds the efi pump (PRE-COOL FUEL), when its needle and seat or diagphram go bad it has a vent or overflow line that dumps directly to #8 intake runner so he has 2 choices, eliminate it and upgrade (which would require alot of work, parts and some complete knowledge of this system) or buy a repair kit for the VST tank and repair/rebuild it, SmittyOriginally Posted by stevesxm
Platinum Member
Here is a link to another thread with same problem:
502 EFI same fuel injector keep getting "stuck" open?? pics, Baja, DVX
If you look at this pic you will see the VST tank in right hand corner
i knew about the VST thing but didn't realize it had a mechanical needle and seat... geeze... and people don't just throw those away and do a work around ? thank you for correcting me. but will that make the entire system go rich as well ?
Right!
anyone make a kit to get rid of it.
I also have a 93 Formula with a 502 now that I know more about it would like to get rid of it.
Platinum Member
The first hint of any problem and I would have it torn off and in the scrap bin, the VST (pre-cool fuel) mpi's also had problems with vapor locking, the tank seems real redundant but unless a guy had a complete cool fuel system lying around off a newer mpi motor the solution would be to build a new fuel system similar to what I did on my 2000 502 mpi when I supercharged it but on a smaller scale.
To do this you would install a efi inline fuel pump feeding from the water seperator/fuel filter, you would send fuel thru a small cooler like a baby oil cooler or PS cooler, you would then feed the fuel rail preferable in 2 places (i did my stock one when I was still using it at front and the side). I also ran my fuel un-restricted straight thru the regulator to the rails and bled off the excess fuel back to the inlet side of the fuel filter/water seperator. To buy the fittings, a cooler, pump, hoses, regulator you will spend a minimum of 500$ or more and with stock hp this would all be totally un-neccesary but you won't ever have a vst to go bad again or have vapor lock problems, Smitty
The early mefe systems are almost 20 yrs old. The crud that grows in the vst tank will always win. If it had a drain you could dump every week it would save the seat. The next problem you would have to fix is vapor lock. In my case the po thought he could fix anything. My end of season fix was to remove it all and go to the scrap yard. Marine HEI Holley Marine carb and Merc intake. The best thing I could do with the mess that I had. I lost a few mph on the top end. No vapor lock or gas dumping in number eight. This is the first summer my wife was not all over me saying why wont the boat start after a hard run.
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