1994 Z240 7.4 Merc won’t fire
 

HELP. Just bought a 1994 Mariah, seller hot wired it in order to get it sold. Put it back together correctly, everything works and motor runs perfectly. After thirty minutes at relatively low power on the lake, I pushed it up and at 3000+ RPM the engine quit. Hasn’t fired since. Replaced coil, signal amp, and optical sensor under the distributor cap. No luck. I have 12 volts at the coil, engine turns over ok, definitely have gas at the carb. Just will not fire. All gauges work, oil pressure ok, I get a little pressure during cranking. Any ideas?

Note, kill switch ok, all CBs check good.

Re: 1994 Z240 7.4 Merc won’t fire
 

Did you replace distributor cap and rotor? When I got my boat it would idle great all day but like you say when I get up higher in the rpms is was cutting out and falling on its face as if I was turning the key off and on. Lots of corrosion under the cap when I replaced it...

Re: 1994 Z240 7.4 Merc won’t fire
 

Thx
The cap and rotor looked like new, the engine had obviously been worked on as all hoses, belts, etc looked like they had been recently replaced. The engine didn’t sputter at all, just flat quit. I still suspect a wiring, short, or safety feature shut down the engine…..a clue might be that the water temp gauge only got up to 110 or so after thirty minutes of low power running?

Re: 1994 Z240 7.4 Merc won’t fire
 

Mechanic informed me that the oil pressure Switch, not sender, can fail and cause a no spark condition, even if the oil pressure is in limits! Ordered a new switch, I’ll post if it works. Thx all!

Re: 1994 Z240 7.4 Merc won’t fire
 

Got to love electrical gremlins!