OMC King Cobra Engine Failure - Overheat or Electrical?

[Trapper John]

Background: '92 Seaswirl w/5.8l/351 Ford and OMC sterndrive.

Symtom:

Boat runs for 10-15 minutes @1000 rpm through no-wake zone. Within 5 minutes after hitting 2500 rpm, engine begins to run rough until rpms drop to 750 - then she stalls out. Temp gage says 120. Problem appears to be thermal because a 5 minute rest will allow a restart, but failure reoccurs more rapidly.

Starter will not turn over immediately after stallout. After rest interval, ignition occurs normally. Alternator output checks out. Batteries check out. New coil, distributor, and ignition module this season.

Suspicions: water pump impeller, faulty shift interrupt switch and/or ESA, or both. Any advice? Thanks!

 

[Don S]

Re: OMC King Cobra Engine Failure - Overheat or Electrical?

Seen bad drives cause the same thing. Bearings so full of metal they overheat, expand and stop the engine.
Drain the drive oil and look for shiny stuff in the oil.

 

[jspringator]

Re: OMC King Cobra Engine Failure - Overheat or Electrical?

I have a 5.8L OMC, and it has a Cobra outdrive; not the King Cobra. As I understand it, these were reserved for the big blocks. If you are having drive problems, you will be happy you don't have a King.

 

[Trapper John]

Re: OMC King Cobra Engine Failure - Overheat or Electrical?

Thanks, Don, I hadn't thought of that - especially since I recently had the drive serviced.

'Gator, I do indeed have the King Cobra drive. Should I open my veins now??

 

[Don S]

Re: OMC King Cobra Engine Failure - Overheat or Electrical?

Don't get too worried about the"King Cobra" name.
There were THREE totally different drives called "King Cobra"
One had very little exposure and only on 460 engines (as I recall) Cone clutch, Little use.
The second was just another name used. Dog clutch, water pump on the back, just different decals
The third didn't start till 94 and had Volvo guts in the drive.

NOTE: These are very minimal and basic discriptions.

 

[jspringator]

Re: OMC King Cobra Engine Failure - Overheat or Electrical?

I wish you the best. I haven't heard anything good about the KC, although I have no personal experience. My Cobra has served me well since 1989 with few issues; none that weren't operator induced, like the drive going aground while on plane at Ono Island in Perdido Key, FL. Ouch!

I have been looking at some 4 Winns Liberators with KC's, but have been afraid of them.

I hope your issues aren't drive related.

 

[HT32BSX115]

Re: OMC King Cobra Engine Failure - Overheat or Electrical?

Nothing wrong with a Liberator!!




Cheers,



Rick

I wish you the best. I haven't heard anything good about the KC, although I have no personal experience. My Cobra has served me well since 1989 with few issues; none that weren't operator induced, like the drive going aground while on plane at Ono Island in Perdido Key, FL. Ouch!

I have been looking at some 4 Winns Liberators with KC's, but have been afraid of them.

I hope your issues aren't drive related.

 

[jspringator]

Re: OMC King Cobra Engine Failure - Overheat or Electrical?

HT, you are the reason I am afraid of KC's. I am not about buy myself into a situation where i have to repower a 21 year old boat.

I would love to have a 24 or 26 footer with a single 454. I could figure out a way to solve the Alpha one problem.

 

[HT32BSX115]

Re: OMC King Cobra Engine Failure - Overheat or Electrical?

You're probably ok with a Cobra.

Just DON'T get one with a 460. There's no manifolds or couplers out there.... (and I found out no electronic ignition parts for a 90 460/7.5L either) Most of the parts for other Cobras (engines) are are pretty much available.


Aw they're not that hard to repower! I only started the project in DEC!! I just got it running yesterday!!

There were times I would go for weeks not working on it! I spent a lot of time just looking at hoping it would install itself!!

The Liberator runs pretty good with the Bravo III now. It was worth it!

It would probably run fine with a 351 powered Cobra too. (there is absolutely nothing wrong with a 351!) Mine ran pretty much flawlessly for almost 18 years with the 460 King Cobra too!
I think my Brother flattened the cam by running the 460 at 300-400 over the max RPM....He probably didn't know he was damaging it...

HT, you are the reason I am afraid of KC's. I am not about buy myself into a situation where i have to repower a 21 year old boat.

I would love to have a 24 or 26 footer with a single 454. I could figure out a way to solve the Alpha one problem.

 

[Trapper John]

Re: OMC King Cobra Engine Failure - Overheat or Electrical?

Bump. Sorry folks, but this thread appears to have been inadvertently high-jacked. Let me start over with my problem because I have been pouring over schematics of my ignition and engine cabling.

Although I haven’t actually checked water flow from the impeller yet, the fact that my temperature gauge is “comfortable” at 120 degrees suggests the problem described above isn’t thermal. If this is correct, describing the problem would sound like this:

Engine runs fine initially at 1000 rpm or less. After increasing rpm to 2000, within five minutes engine begins to stutter until it stalls out. After stalling out, either (a) starter motor will not turn over at all, or (b) starter will turn over but engine will not fire. In either case, waiting fifteen minutes or so will result in smooth and instant ignition. Engine will then run smoothly for ten or less minutes. Process then repeats itself.

Inspection of the engine cabling schematic reveals four likely suspects:

1. The main cable connector
2. a common ground on the engine block
3. The electronic shift assembly module (ESA)
4. The shift interrupter switch.

I could add a fifth suspect if I throw in the shift/throttle unit itself.

My theory of the break-down cycle goes like this:

A defective ESA tells the shift interrupter switch to close. It does its thing, thereby causing the engine to stutter. Since the throttle is open for 2000 rpm, when the current is interrupted the engine effectively floods. (This would explain the wait time before successful ignition occurs.)

I think the hole in this theory is that it doesn’t explain why the ESA/interrupt works fine initially.

Any thoughts? It’s tough for me to do on-the-water diagnostics because the “water” is the Columbia River! Between wind, tide, current, and commercial shipping, finding sea room to get the boat going fast enough to induce a failure is dicey.

If you’re still reading, Thanks for putting up with this long post!

 

[Haut Medoc]

Re: OMC King Cobra Engine Failure - Overheat or Electrical?

I'm not an OMC guy, but......
Is it not similar to a shift interrupt switch on a Merc?......
Since the drive will go into gear with it disconnected, why not disconnect it & see if it still does it?........​

 

[Haut Medoc]

Re: OMC King Cobra Engine Failure - Overheat or Electrical?

Another thing that might cause this is mechanical overheat.....
Don S suggested the drive.....
What about the engine?......
Have any diagnostics been done to it?.....
How is the oil level & pressure?......
Timing correct?.....
Compression test?.....
That sort of stuff......
Did/does it get to WOT?.....
Does it perform normally until it doesn't?.......​

 

[Trapper John]

Re: OMC King Cobra Engine Failure - Overheat or Electrical?

Another thing that might cause this is mechanical overheat.....
Don S suggested the drive.....
What about the engine?......
Have any diagnostics been done to it?.....
How is the oil level & pressure?......
Timing correct?.....
Compression test?.....
That sort of stuff......
Did/does it get to WOT?.....
Does it perform normally until it doesn't?.......​

This engine came out of dry dock in May and all of the above checked out. Prior to this problem WOT was achievable. Performed "normally" until problem first reared its head. OIl level, temp a guage as normal. New oil pump in May.

Coil burned out in June. Replaced coil and ignition switch. Emergency shut off switch replaced in May. Replacement malfunctioned after first incident of current failure. (This is weird - isn't the emergency shut-off a mechanical device - it's either held closed or open when tripped?) Sorry guys, this is a tough one to describe.