With no codes being shown for any form of crankshaft failure and the engine restarting and running after cool downs I am suspecting you may actually have a fueling issue which is cutting the engine out and then seeing some backfiring (popping) on attempted restart. Get a fuel pressure guage installed on the problem engine and watch it closely when it first runs and then under load when it stalls or stops. Is the fuel pressure at 43psi key on no start, idlers about 43-41psi and stays above 40 psi when at full throttle and where does the fuel pressure go before or just before it quits or stalls?

Is the engine quitting or stalling when you back off the throttle or quickly reduce speed?

Best Regards,
Ray @ Raylar

I didn't think of using a scope, at least that would tell if the wiring or possibly the computer is bad. I have a hard time believing that 2 new sensors are bad, but who knows. Also, if it was an issue with the crank/ bearings shouldn't I also see other symptoms?

Thank you for your advise.

I never thought about it being a fueling issue. I will get a fuel guage on it and see what happens. Does the computer shut down the engine when it senses low fuel pressure? Would it not set a code?

The engine has never quit or stalled when coming off the throttle. It has quit at idle (after idling for several minutes), it has also quit at 3000 rpm or 4000, doens't seem to have any reason. When it does quit, it has never fired right back up immediately.

Even though everything seems good and tight, I am going to double check all grounds and fuel pump wiring, in fact i will look over all wiring and connections.

Any chance this could be cam sensor related? I'm guessing the computer needs to see both the crank and cam positions to give the spark signal??

Thank you for the help.

Checking all the connections and grounds is also a great idea and it could be an intermittant connection. The cam sensor could be bad also, try swapping between the two engines on the cam sensor and see if the problem moves with the sensor.. The cam sensor is NOT a real expensive part when bought at a auto parts house or GM, so you could just try a new one. The cam sensor won't cause the engine to quit or stall but it will make it hard to start and can pop as described on starting if its bad or intermittant. Usually it will throw a code though for cam sensor issues.

Reason I asked about stalling when pulling back throttles is if an IAC is acting up or bad it will cuase a stall many times at throttle pullback transitioning to idle as that is where it also works to stabilize the engine rpms backing down. Doesnot sound like this is in play here.

Best Regards,
Ray @ Raylar

Here is an update. --And hopefully a conclusion. Possibly help someone else with a similar problem.

I swapped both crank and cam sensors between engines. It took a while but the port (previously reliable) engine gave me the rpm flutter. Not knowing which sensor it was, I moved the cam sensor back to the starboard engine and the problem followed. I replaced the cam sensor and the problem seems to have gone away. Funny it is both the cam and crank sensors on the same engine and the other has been flawless.

So, the symptoms this bad cam sensor has given are engine flutter (tach drop by approx 1000 rpm for an instant and recover), completely die at any given rpm and not restart right away (had it happen at idle and 3000 rpm), sometimes no start when hot. Always started when cold. Never threw any codes which I understand is unusual since a cam sensor usually throws a code.

Thanks to everyone for the input. I am considering it solved.