zschaefer38

1997 Powerquest, twin 502 efi/mpi, with mechanical fuel pumps, and vst tanks. What i have done already: Coil, cap, rotor, mechanical fuel pump, checked anti siphon valve and pick-up in tank, module, fuel filters. What happens: Running along anywhere above 3k rpm and the starboard engine will suddenly lose rpms. If I power down quickly, I "catch" it and it will keep running at idle or slightly above. If I dont catch it she will eventually studder and stall. I power down to idle, stick it i neutral and she fires right back up. This happens intermittently and it doesnt matter if its a flat lake or rough. I did all this work and she will run fine for two maybe three weeks then bam, comes back to haunt me! Especially on a POKER RUN!!!!!!! I have not checked the vst tank yet but I am starting to get indication it may be the filter in the vst or the fuel pump in the tank. One thing to note, this happened only twice last year. This year has done it a dozen times and thats when I started throwing parts at it (based on friends recommendations). Also, this got much worse since I ran out of fuel last month (faulty gas gauge) . Lastly, if I keep the rpms below 3k, around 2600-2700 she seems to run ok but the rpm needle does seems to float a lot. Any ideas people?????

zschaefer38

Not a single clue from the 60+ people that read it??????????? Give me something here, these are very common engines I know someone has at least a clue or advice!!!! BTW, pulled off the vst cover last night and the micron filter had some debris on it, but I was expecting to see more.......

Griff

Clean the screen in the VST.

zschaefer38

I did when i had it off last night, it didnt look terrible so i used brake cleaner and blew anything i could out of it.....someone said that the high pressure pump that screen is attached to may be going....does this make sense?

28Eliminator

If the mechanical pump starts to go bad and can't keep up, the VST pump pulls most of the fuel out of the VST tank, then you loose high fuel pressure. If you change the oil in the sea water pump that drives the manual pump it will usually be full of gas (mixed with the oil) if the pump is going bad. Next time it happens you could pull the plug off the top of the VST tank and stick something clean down the hole to see where the fuel level is at, It should be almost full. Since the introduction of ethanol, those old manual pumps don't last very long. I'm guessing the new pumps have changed the diaphrams to work with ethanol.

zschaefer38

I do have a new mechanical fuel pump on that side, thats the last thing i changed, in the middle of lake erie, and the problem arose again. So now, I took apart the vst take and cleaned the micron filter on the bottom of the high pressure pump. It didnt look "that bad" not like caked with junk like I was hoping it would but it needed cleaned. Replaced the o ring seal and put it back together. I ran for a few minutes last weekend but not long enough to test it but she ran ok. I will know more tomorrow when I run the islands.

MER Performance

Do you have any data on your fuel pressure after the VST. going to the injectors? Sounds like you fuel pressure is down.

zschaefer38

Not yet, I was gonna throw a gauge on the fuel rail if this didnt work. I picked up a mechanical gauge from a buddy but never got to installing it cause it didnt have all the connectors i needed.

johnny b good

Are you using ethanol fuel? And or mixing ethanol with non ethanol fuel? It can cause issues. I would at least try to use pure fresh gas to eliminate that possibility and a fuel pressure gauge hooked up to see what happens when your issues arise.

justinp20012500

Identical to what I have been chasing for months...

http://www.offshoreonly.com/forums/g...-run-time.html

It will run 20 or 30 minutes at or near WOT, then as soon as some heat is built up it acts up. If I run it at 2500 RPM's or below it will run all day long and not a single issue. I have a fuel pressure gauge on the rail and have monitored it when it acted up. Also tried to pull codes. Nada...