Logo
FULL SITE MENU

4.3 Overheating/Fuel Pump Question

P

Putz1699

New member
I have a '88 4.3 Mercruiser. I switched the fuel pump to an electronic fuel pump because the mechanical pump was too expensive at the time. I'm wondering if I missed up here. We took it out, and getting up to plane it began to struggle and overheat. I figured it was a carb issue, since we just pulled this boat out of the back pasture after sitting for 2 years. I got everything tore down, then realized on the side of the carb, there is a port for what I believe would be high input fuel? My electronic pump does not connect to that port on the side of the carb. It does start and idles just fine. Would that cause the motor to weaken and overheat at higher RPM?

I know the overheating isn't a cooling issue. I have a new impeller, manifolds and risers have been checked. Trying to figure out the motor weakening and over heating.

Thank you. I am a mechanic, but I am not a marine mechanic so I'm learning as I go.
 
I know the overheating isn't a cooling issue
Wrong, thats the first place to look Either not enough water getting in or not enough getting out. If you replaced a mechanical pump with an electric one the clear or yellow hose that went from the pump to the carb is no longer needed
 
It's building heat because the motor isn't running right, it's missing at higher RPMs, it'll get to 150-160 degrees and it starts missing, then the temp sky rockets. There's no restrictions as far as water flow through the motor.

The hose isn't needed, that's good to hear because it's not on there at this point haha. I have a carb kit on the way, the gas that was in the motor was severely varnished so I'm doing a full tune up and carb kit. Need to order intake gasket for it, dealership didn't have one. Going to get that done and get it out on the water and see where it stands.
 
Basic engine gaskets are no different than automotive. With the exception of the marine head gaskets. SO the intake gaskets can be had at a auto parts store.

when a boat sits for an extended period of time,
1. replace water pump impeller (Whole kit).
2. remove fuel from tank and put in new fuel.
2. As you are doing, Carb needs thorough cleaning.....

make sure the miss is fuel related, After sitting it is not that far fetched that the dist cap and what lurks inside may need to be looked at.........Moisture and possible corrosion......

V6 is notorious for warped heads due to prior overheat condition, so pull plugs and check to see that they all look the same.
Check compression as a bad head gasket between water and combustion will cause issues as yours.

it is weird but when a boat sits for extended time and if not stored in a temp controlled garage strange things can happen

The high temp rise all of a sudden does not sound like a fuel related issue. If you have access to a infa red temp gun, conform temps first.

A bad sender will act as you describe...........stable then shoot to the moon

That port is for mechanical pump, if the diaphragm ruptures gas will flow thru the line to carb, On an auto it would flow to the ground.
 
I'll bet that electric pump of yours is supplying insufficient fuelto run the motor at high throttle.

Been down this road myself of late, and I can attest that--unless the pump delivers a steady 5 psi or more at WOT--the motor will lean out and overheat; and lots of fuel pumps out there are not up to the task! I went through four of them before finally coming up with a goods one.

First thing I'd do is to temporarily install a 0 to 10 psig pressure gage before the carb, then open her up (on plane) and see what pressure is being maintained. If the pressure drops below 3 or 4 psi, that's the problem.

Jeff
 
Back
Top