OMC loses power... fuel cut / rev limit problem?

[adam355]

I have a 92 Forester 170 sport with a 4.3L OMC I/O

Once I start to creep past 30-35 mph the boat will randomly lose power. If I stay under 30 all day I wont see it happen. Even when Im giving it full power to pull wakeboarders up.

I'm not sure if its a rev limit or if its a fuel issue. I had a mechanic look at it over a year ago who replaced the distributer cap? but that didnt seem to solve the problem.

I might be taking the boat out tomorrow so if I could get any ideas what to look for I would really appreciate it!

 

[Howard Sterndrive]

Re: OMC loses power... fuel cut / rev limit problem?

fuel issue.

that.

start with a new fuel filter

If a mechanic changed the entire distributor cap 1 year ago to address this issue..... , it might be time for a complete tune up and all the prescribed maintenance.
When was the flame arrester last washed?

maybe a rotor to go with that new cap....

most high rpm power issues are fuel delivery related. check the tank vent...

but the word randomly in your description could be ignition coil too

 

[reavesga]

Re: OMC loses power... fuel cut / rev limit problem?

Does it lose power and settle at lower power setting, or does it completely lose power and all but die?

 

[adam355]

Re: OMC loses power... fuel cut / rev limit problem?

It just briefly loses power and then kicks back in. Never dies

 

[adam355]

Re: OMC loses power... fuel cut / rev limit problem?

that.

start with a new fuel filter

If a mechanic changed the entire distributor cap 1 year ago to address this issue..... , it might be time for a complete tune up and all the prescribed maintenance.
When was the flame arrester last washed?

maybe a rotor to go with that new cap....

most high rpm power issues are fuel delivery related. check the tank vent...

but the word randomly in your description could be ignition coil too

What is the flame arrester?

Its random but if im WOT its going to drop power within 5 - 10 seconds for sure.

 

[cr2k]

Re: OMC loses power... fuel cut / rev limit problem?

The thingy on top of your carb. I would also consider water in the carb or fuel.

Also pull your dist cap off and make sure the rotor will turn and spring back, there is about a 15-20 degree spring loaded centrifugal advance system in the dist. If this is not working you can have problems too.

Since you asked what a flame arrester is you might want to have a more mechanically knowledgeable friend help you.

 

[adam355]

Re: OMC loses power... fuel cut / rev limit problem?

Ok Thanks for your help guys. I will take a look hopefully this evening.

 

[bruceb58]

Re: OMC loses power... fuel cut / rev limit problem?

And one someone gets on here and starts suggesting changing the coil, ignore him. Sounds like fuel.

I would suggest running from a seperate portable tank to get the tank out of the equation.

 

[Howard Sterndrive]

Re: OMC loses power... fuel cut / rev limit problem?

And one someone gets on here and starts suggesting changing the coil, ignore him.

yeah, never change a 19 year old coil...

 

[bruceb58]

Re: OMC loses power... fuel cut / rev limit problem?

99% of the time its never the coil. The coil isn't getting stressed any more at 3000 RPM vs 3500 RPM. I wonder how many spare coils are sitting in people's tool boxes because its the first shotgun troubleshooting step.

 

[Howard Sterndrive]

Re: OMC loses power... fuel cut / rev limit problem?

it was the "random" part that had me thinking electrical or fuel

hmmm... anti siphon fitting at the tank might be a good starting point...that could act up randomly

 

[bruceb58]

Re: OMC loses power... fuel cut / rev limit problem?

Seems to me that the fuel system needs to be diagnosed first and running on the external tank gets all the tank stuff out of the picture.

 

[reavesga]

Re: OMC loses power... fuel cut / rev limit problem?

Its is most likely fuel. If after going to wide open throttle it loses pwr for a few seconds and then comes right back and keeps power I am guessing the needle valve metering fuel into the bowl of the carb. It can randomly stick and cause this. Vibration shakes it free and all is good again. Before rigging up fuel cans I would have a competent tech put a carb kit in it.

 

[whitney]

Re: OMC loses power... fuel cut / rev limit problem?

I had a very similar problem with a 92 OMC 4.3. Definitely check fuel first. I did. I plumbed in a fuel pressure gauge and could watch pressure when my cutting out and power loss was happening.

I learned a lot about my fuel system in the process of diagnosing it, based on a lot of great advice from here. Here is my test rig:

Turns out my fuel system was FINE. 8 psi all the time. Good check valve, clean filters, no obstruction. But I'm glad I did it first to be sure.

So guess what, on my boat it was a bad coil. This is what a bad coil looks like. Very hard to see on my OMC without pulling it, had no idea it was this bad. Sure the load is not much different on the coil at 3k or 5k, but it definitely gets warmer the higher the load.

Admittedly my symptoms were a bit different than yours and were in retrospect temperature dependent. I could run the boat at top speed first time out, and performance would fall off over the day. But I could always do a WOT holeshot with the cutting out happening after 5-10 seconds.

 

[NHGuy]

Re: OMC loses power... fuel cut / rev limit problem?

Check that the fuel lines aren't dried-cracked too. Mine were, and were part of the cause of a high rpm surge I had. You can check for intake manifold and carb gasket leaks by squirting carb cleaner around the edges of the carburetor base and the outside edges of the intake manifold. If the engine speed picks up when you spray there's an intake leak there.

My boat is only a couple of years older than yours. If your lines look original I recommend doing a complete fuel line change, anti siphon valve removal and cleaning, fuel filter change, and fuel separator/ filter change. 20 years is a long time for rubber fuel lines.
I'm a little anal so I did those items plus cleaned my tank vent, replaced my vent line and replaced my fill tube when I did the fuel line service.
It is worth the effort. When everything works right you get full power, a quick start and best behavior.

 

[superbenk]

Re: OMC loses power... fuel cut / rev limit problem?

I had a very similar problem. Check anti-siphon & vent lines first (AS valve is a $8-10 fix).

 

[Chuckyd973]

Re: OMC loses power... fuel cut / rev limit problem?

Sounds like and Ignition Float. If its points then change the points and condenser. The points cant kep up with the rotor at the higher rpms. My 3.0 had the same issues. Would run all day at 3500 rpms then when youtry to go wot it would cut out.

Chuck

 

[TLL]

Re: OMC loses power... fuel cut / rev limit problem?

"It just briefly loses power and then kicks back in. Never dies"

This is a classic shift system adjustment problem. As you accelerate, the shift cable actually pulls the vertical drive into gear a tiny bit more. This is causing the shift interupter circuit to activate. The interupter switch activates the ESA module, causing intermittent spark for about 5 seconds, then the module times out and the engine runs normally. Confirm this by observing the shift system "V" notch and switch while you accelerate, if the "V" notch lever moves and activates the interupter switch when you hit about 30 mph, you found your problem. You will need to adjust the shift system or find out why shift cable loads are causing a false activation of the switch.

 

[float2]

Re: OMC loses power... fuel cut / rev limit problem?

99% of the time its never the coil. The coil isn't getting stressed any more at 3000 RPM vs 3500 RPM. I wonder how many spare coils are sitting in people's tool boxes because its the first shotgun troubleshooting step.

Never say never. Maybe its not the coil itself but check the coil WIRE and make sure its seated tightly on both ends making good contact. I had this happen on my OMC this summer I was running fine and all of a sudden I would seem to lose power, then pick-up again, lose power..............

If its not a bad coil wire connection could be some of the things already mentioned in this thread.

 

[adam355]

Re: OMC loses power... fuel cut / rev limit problem?

I brought a spare tank down to the boat and my starter took a crap on me.... great luck.

It took long turns to get started and once it did it died after running it for a while. (normal: cold engine) I tried it again and it wouldnt turn over at all. Its grinding really bad and chattering/clicking so im pretty sure its the starter. The battery is fully charged

looks like i have something else to fix first now...