HiPerf2000

iTrader: (2)

1996 502 mpi's. Recently had the top end off of one motor cause i thought i had a head gasket problem (ended up being a flapper in the "y" pipe that was the problem). Had the heads done while off and Motor had good compression.

Now the motor is burning twice as more fuel than the other. We put the computer analyser on it and all it didn't show any codes or problems. I have 2 tanks in the boat and if i fill them both this motor will be empty while the other is still on half. So this motor is buring twice the fuel.

I checked the oil and it is normal. the transom is not black. there is no fuel in my bilge. the gauges are correct. Where is this fuel going?????

What can i check???

Vinny P

While I am not an expert on twin set-ups, that just does't make any sense. If one motor was burning that much more fuel, you would have to see some result of the extra unburned fuel. Whether it is in the oil, soot on the transom, or something somewhere.

I seem to remember from the few times I have messed around with my Quicksilver scanner, that there is a parameter in there that will show you fuel usage. Maybe you can scan it and see if there is a difference between the 2 motors.

MnFastBoat

I too am interested in these findings
I have '99 502's and mine have done this since new
Not as much as you are inquiring, but I do burn more on the port side then sb.

Sonic30ss

I had a problem like this, it turned out the coolant temp sensor plug male end was not making proper contact with the female end, so the ECU thought the engine was always cold , therefore it kept it in the cold start mode. Kind of like a sticky choke(except you can't see it) OH yea I almost forgot ....that motor used exactly 2X the fuel of the other, get it now or bye bye rings!

HiPerf2000

iTrader: (2)

Would this sensor problem show on the scanner??

Sonic30ss

I don't know, my system is older, and I did not have a scanner for it.
I'm just trying to give you an idea where to look. With the FI systems the coolant temp is what controls enrichment so, it seems a logical place to look. Is the tstat stuck open and not allowing the engine to get to normal operating temp??

HiPerf2000

iTrader: (2)

dont think it is a t-stat problem cause it runs at 170 degrees. maybe i'll swap coolant sensors to see if thats it.

DanB

I posted this on another thread..but I dont know how to link them. I had the same problem as you. Would burn much more fuel on one engine for the same amount of running time.

"Had the same problem. Early style VST diaphragm went bad sending fuel to #8 cyl. I wound up getting the new style that dumps fuel back to the mech fuel pump return line. Be careful..if you run it that way you could wash down #8 and need a ring job. Or worse."

It turned out it was his VST. If I were you I'd look at that as your problem.

Dan

articfriends

iTrader: (1)

VST diaphram going bad and dumping fuel to # 8 must be fairly common,A friend of mine just rebuilt his 502 with early merc fuel injection and had same problem upon initial startup(this had been a two year project and had been sitting a while).

HiPerf2000

iTrader: (2)

i did a search on threads that are VST related. They say to check the diaphram for a possible leak is to put a clear hose in place of the vent hose....and you will see fuel flowing though.

question......can i do this with the boat running on the trailer? will it happen at all RPM's?

i have the hose off and am picking up a clear hose tommorow and will give it a try tommorow night.