92 omc 5.7 mid-range stumble/misfire

[jmacgowan]

I have a 92 omc 5.7, runs perfectly until approx 3000 rpm then engine stumbles or misfires. recently rebuilt upper, new drive, new carb, full tune up, I have checked out all fuel lines, any suggestions?

 

[Bondo]

Re: help

Re: help

Ayuh,... Sounds like it's Still staving for fuel...
How much Crap was in the filters,+ fuel lines,..??
was the carb rebuilt After the rest of the system was trouble shot,..??

 

[jmacgowan]

Re: help

Re: help

filters clear, lines clear, carb brand new. I just pulled the fuel pump, when working it by hand while blocking the inlet, I can hear the check valves hissing inside. so I belive that we need a fuel pump. next problem is the pump that came off is not listed for this boat, I have a 5.7 litre omc the flange id # is 69489. this part number in the omc parts book says it is for a v6 ?

 

[Bondo]

Re: help

Re: help

Ayuh,... They could very well be the same...
Click on the OMC parts links at the top of this page,+ run it down to see what's available thru Sierra...

 

[jtybt]

Re: 92 omc 5.7 mid-range stumble/misfire

Is the stumbling happening while the engine is still trying to accelerate or at a steady throttle setting?

Fuel related is the moist likely but electrical/ignition still can't be rulled out at this point.

I had the same problem at 3400 RPM on a brand new electronic ignition system so I did a complete fuel system check...including 3 different carbs. Turned out to be the new ignition system.

 

[jmacgowan]

Re: 92 omc 5.7 mid-range stumble/misfire

the problem happens above approx 3000 rpm, if i throtle down a couple of hundred rpm and hold steady it clears up. Oops, forgot to mention before i pulled the fuel pump, while running with a new clear plastic inline fuel filter, i noticed that the filter was almost empty with just a trickle of gas along the bottom

 

[jtybt]

Re: 92 omc 5.7 mid-range stumble/misfire

Gotta check the anti-siphon valve on the gas tank. They can get clogged or sticky (along with the pick-up tube)


There's also a possibility of leaky fuel line or connection that's sucking air at higher fuel demand.

 

[jmacgowan]

Re: 92 omc 5.7 mid-range stumble/misfire

thanks, the anti siphon valve is clear, the screen at the end of the pickup is clear, checked both twice. I will check all fittings for air leaks when I figure out what fuel pump I need

 

[jmacgowan]

Re: 92 omc 5.7 mid-range stumble/misfire

update, I replaced the fuel pump, Checked out all fuel lines, still had a problem, pulled the NEW ponts, replaced them and problem is solved, I heard that "bouncing points" is a wives tale, any suggestions on what was happening?

 

[Don S]

Re: 92 omc 5.7 mid-range stumble/misfire

Some point sets have a C shaped secondary spring that fits around and with the copper strip when mounting the points. If that was missing, there just isn't enough spring in the copper strip to close the points fast enough. I have run into this on several boats, but it usually happens at 1200 to 1500 rpm.

 

[jmacgowan]

Re: 92 omc 5.7 mid-range stumble/misfire

nope, the spring was there, and it ran great for 5 hrs before the problem started

 

[FreeBeeTony]

Re: 92 omc 5.7 mid-range stumble/misfire

. recently rebuilt upper....

Are you talking about the top of the engine? Is it possible the valves are too tight? I had a similar problem and it wound up being valve train related.........just a thought.

 

[jmacgowan]

Re: 92 omc 5.7 mid-range stumble/misfire

yes, I wondered about that but dismissed the idea due to the fact that it ran great for 5 hrs before giving trouble ?