Mercruiser 5.7 Stalls Under Load After Rebuild

[Pbober]

Hello,

My son replaced my 1996 5.7 Mercruiser, two barrel, pre-vortec engine in our 20' Reinell due to a cracked block. The engine was rebuilt by a professional rebuilder.

They were unable to find a block drilled for a mechanical fuel pump and so we installed an electric fuel pump (Sierra 18-7326). Also put in a roller bearing cam and flat top pistons. Replaced points, plugs, cap, wires, fuel filter, bellows, etc. as well.

Engine runs great in neutral but underway seems to run out of fuel at at about 2800 to 3000 RPM. If you pull back on the throttle it will avoid stalling. We can not get it up on a plane.

We thought maybe it was a fuel issue, but used an auxiliary tank with clean fuel and the same thing happened. My son thinks a four barrel carb is needed, however my brother-in-law thinks increasing the float level of the original carb would fix it. I wonder if it is something else such as a vacuum leak, bad fuel line, or maybe something in the carb.

We are at our wits end on this!

Has anyone had a similar experience?

Thanks!

 

[DeepBlue2010]

Welcome to iBoats..

What was your contract with your engine builder? Does he build the engine, install the peripherals and get the engine tested and running or he just rebuild the block?
The electronic fuel pump might not be able to supply enough fuel at this RPM, the carb might not be jetted correctly


I would thank my son and my in-laws for their contribution so far but the amount of variables in this situation needs a pro to untangle the possibilities.

 

[garbageguy]

Interesting. We (mostly my son with help from a seasoned mechanic) just replaced the 5.7 in our 24 ft Wellcraft because it was worn out. Got a marinized long block, and put most of the stuff from the old engine on the remanufactured. Had to replace the mechanical fuel pump with electric. Had a fuel supply problem that turned out to be (so far) a bad anti-siphon valve. Not sure if that's your problem, but it's pretty easy to check out.

 

[72GT160]

Anytime you have run ability issues check to make absolutely sure ignition system is working properly. THEN look into fuel system. You can very easily have crossed a plug wire and not hear a change or not have proper timing set, points set, etc. Start with elec. and go from there.

 

[Pbober]

I had similar thoughts about the fuel pump and the anti-siphon valve is not something I am familiar with.. The rebuilder was only responsible for rebuilding the engine.

My son, is about ready to throw in the towel, so we may need to take it to a professional.

Thanks for the responses so far.

 

[Eric 3.7LX Alpha 1]

The anti-siphon valve is in the fuel tank so if you ran a remote tank that's ruled out...

What's the timing at? and the dwell?

How does the timing advance springs look under the points plate? If they're rusted they won't move correctly when you need them to..

There is a chart in the service manual that shows what the timing advance should be at... at various RPM's, you'd need an advanced timing light to check it. I can put a link to the chart if you need it.

You could also put a temporary inline fuel pressure gauge between the pump and carb using fuel hose and clamps.... and keep an eye on it while on the water see what the pressure is when it acts up.

 

[Pbober]

The timing is set at 32 total advanced. The distributor is a modular controlled distributor. Son is pretty sure the springs were clean, but we can double check.

We already installed the fuel pressure gauge between the pump and carb and it was at 5 PSI.

 

[Bondo]

They were unable to find a block drilled for a mechanical fuel pump and so we installed an electric fuel pump (Sierra 18-7326). Also put in a roller bearing cam and flat top pistons. Replaced points, plugs, cap, wires, fuel filter, bellows, etc. as well.

We thought maybe it was a fuel issue, but used an auxiliary tank with clean fuel and the same thing happened. My son thinks a four barrel carb is needed, however my brother-in-law thinks increasing the float level of the original carb would fix it. I wonder if it is something else such as a vacuum leak, bad fuel line, or maybe something in the carb.

Ayuh,.... Welcome Aboard,..... What/ Why is a 1996 Merc got points in the distributor,..?? it oughta have been a T-Bolt V,....

A roller cam, 'n flat-top pistons Deserve a 4bbl. carb,.... Can't believe it wasn't in the original recipe,...

It could be a vacuum leak, could be a bad fuel line,....
A brand new motor deserves to atleast have the carb Rebuilt, though a New Edlebrock, 1409 would be a Better choice,....