WhatmeWorry

[Ksch439928]

I have a 1988 OMC 3.0 Liter that has a mystery illness ! I have seen this situation in older posts ,so it must be "somewhat" common. Here is the symptoms. the engine will start and run GOOD for about twenty minutes to one half hour. About ten minutes after it comes up to operating temp it starts to run VERY poorly. No acceleration , miss-firing and such. When you bring the throttle down to 1000 RPM's it will eventually quit. NOW ! when you try to start it after it stalls out it will not start. After about ten minutes it will start , but still being hot it will quickly duplicate this behavior .If you let it cool off "say" overnight it will run GOOD then repeat this whole sequence. This is what I have done so far to rectify this. I have replaced the interrupter and over stroke switch and ESA module. NO dice , changed points and condenser and cleaned distributor weights and made sure all was working properly. Again back to the drawing board. Checked the coil and resistor wire and everything seem within operating specs. but I put on a coil with an internal resistor and wired directly to the alternator. NADA !. WELL what do you think ?? I know these engines are notorious for cracked manifolds but there is no evidence of water in the crankcase, besides even if there was an internal crack wouldn't at least try to fire after it stalls out ??? Has the original fuel pump , have not checked pressure on that yet . This one is testing me! I would appreciate your advise and knowledge on this one.
SINCERELY WhatMeWorry

 

[southkogs]

Welcome aboard:

What does the gear lube in your Stern drive look like?

I'm leaning toward fuel right now, but I don't know the Cobras all that well. I'd be checking fuel flow - cold and at temp, though I don't know why that would matter off the top of my head.

 

[Bondo]

Ayuh,.... Welcome Aboard,..... Durin' the time it won't start, with a test light, is there Power at the coil's (+) terminal,..??

Is the fuel tank vent, free, 'n clear,..??

 

[gm280]

I would look to see if you are loosing spark after getting hot. While the coils look and test out good while cold (resistance readings), they could be shorting out (or opening) when hot. So see if you still have spark when it dies. If not, see if you have anything firing the primary side of the coils... JMHO!

 

[HorizonblueDK]

Back in the old days, my father had the same problem on three 120 HP OMC Stringer engines(two different boats). Running good for 30 minutes, but then starting to misfire and eventually stall at idle. Here the problem was the rotor. The electrical connection on the rotor was riveted together of two parts, and apparently this connection went bad when hot(and old).