OMC Cobra 5.7 gear shifting engine stumble, pop and smoke

andrewtanner80

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Jul 5, 2022
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Hi there,

I have an OMC Cobra 5.7L (Chevy 350) in a Bayliner ‘88 Ciera. After successfully doing an electrical fuel pump conversion, I went to switch into gear, upon which it stumbled momentarily and then there was a pop and plume of smoke came from the engine bay.

I tried again and it just stumbles.

Prior to diagnosing that I had a fuel pump issue, I was careless and connected a 12V ignition cable to a ground coming off the carburetor when I couldn’t get it to start (yes stupid I know but it was a male and female spade loosely next to each other). There was also a really whacky wiring under the dash where the water pump was getting power from the Brown & White stripe wire (Pin 11). This is the trim sender wire but there isn’t a trim gauge on this boat. Again, in a stupid move where I thought perhaps that wiring, I have a feeling I connected a 12V supply to that too (it now no longer provides voltage, and I think it was about 5V previously).

So the Darwin Award goes to me but I am where I am.

I checked the three fuses (because it certainly seemed like a fuse pop), but they’re fine.

I pulled out the ESA for a visual inspection and it looks fine however it’s also fully potted so I can’t see how that could have been the source of the smoke (would appreciate a step by step to electrically check it if someone knows how to do this too).

I’m aware of the OMC shifting issues (having done some forum reading prior to this post), but my shear stupidity is likely the root cause here before we get into shift cable troubleshooting etc. That said, pulling off the stern drive to replace the bellows and gimble bearing is planned so any troubleshooting there too is possible.

Lastly, while this engine only has 130hrs on it, I didn’t shift it into gear before purchasing (stupid #3). It is therefore possible there is a residual issue but I’m still thinking my own stupidity is at fault here.

One positive is that the engine runs like a sewing machine!

Thanks in advance for your help!
 
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andrewtanner80

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So a bit of additional information from tonight’s troubleshooting, for whatever reason when they dropped a new engine in this boat and rewired it, only the overstroke switch (not the interruptor) is connected to the ESA. They have blanked two of the pins. So now I’m trying to also work out whether that’s just the root cause or whether it’s something else all together4A16AF5F-674F-48F2-8BDA-638232E742EE.jpeg10B265EE-C560-4379-9CEB-15083020028C.jpeg
 

andrewtanner80

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This thread is now closed.

My engine had just backfired at low revs which probably had something to do with the new fuel pump and running rich.

I tuned the carburetor and rewired the interruptor in series with the overstroke switch and I’m all good!
 

kenny nunez

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Jun 20, 2017
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Your electric fuel pump should be wired through a oil pressure safety switch.
The pump should only operate when the engine is running so that if the engine stops due to the carburetor flooding over it could cause a fire.
Good job however on the other issues.
 

andrewtanner80

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Jul 5, 2022
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Your electric fuel pump should be wired through a oil pressure safety switch.
The pump should only operate when the engine is running so that if the engine stops due to the carburetor flooding over it could cause a fire.
Good job however on the other issues.
Thanks Kenny. I'll definitely do this!

Here's what's needed for anyone that stumbles on this thread:

Attached is a schematic, and this YouTube video is a helpful explainer
 

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