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Boat died, wouldn't restart, rough idle, efi?

1005 Views 10 Replies 7 Participants Last post by  blackhawk
I've put a total of 3 hours on this boat, and already it's falling apart. It started idling rough, then had died. I was parked for several hours listening to the radio, then cranked it. It started, but sounded like it was missing really bad, then quit. I noticed while it was running, that I was reading battery voltage, not the normal running voltage of 13 volts or so. I tried restarting it, but it would just rev and die. Ended up needing a tow. So I took the alternator off today, thinking that had to be it. Now I don't think so. I did my own bench test using an R/C car starter to spin it, and it's getting 30 volts after voltage buildup. I checked the battery, and it reads 12.63 volts at the posts. (10 at the instrument panel) What else could be the culprit? I turn the key, and the fuel pump turns on each time, although sounded a little wierd on the initial. Any suggestions?

1998 502 EFI Mag
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I also noticed while up on plane the tach was erratic; jumped about a thousand RPM with no noticable increase in engine pitch. Not sure if that's somehow connected to the problem.
Try charging your battery or borrow a new fully charged battery. Electronic ignitions can do funny things if you have low voltage. Also check your connections to the battery and to the ignition systems.
Try Dumping the contents of your fuel/water separating filter into a clear glass jar too see if you have water in the fuel..
I did that, didn't notice any. Real quick...I replaced the filter with one I had from my carbed boat because they looked exactly the same. I read on here (after the fact, of course) that you shouldn't do that because the element can come apart, and, I assume that means send bits of element throughout the entire fuel system. But it was occasionally dieing before I changed the filter, it just got worst the day of. I just took the filter off, dumped the gas, and cut it open. Looks okay, it's not disfigured, missing parts or damaged in any way (other than me chopping it open) The fuel I dumped out of it looks clean with no particles or water.
OK, nothing that simple of-course, but it was worth a shot, so if the fuel is good, and I doubt your charging system or battery is to blame, I'm thinking something is up with your fuel management system or the distributor (ignition/spark). electrical gremlin. Sorry, I'm no expert on the 502 EFI, but try some of these simple checks.

check for spark at a plug .
Check all the plug-in harness connections to & from the distributor, ignition, etc. and check All grounding wires.
Pull the distributor cap off, check connections on the pick-up module, and look for moisture.
Check your fuel pressure at the regulator on the fuel rail.
Note, you have 2 pressure regulators, 1 on the rail, and 1 near the fuel pump & cooler.

It's probably something very simple, but who knows..
Good luck.
RSCHAP1 hit the nail on the head, check your ground cables. I left one loose on my kit car and it led to slow starting and erratic gauges and running issues. Even if they are tight, clean up any signs of corrosion and reattach them.
I will check that, thanks for the tip. It's almost behaving like cars I've had that needed an ECM. How often do those go bad? I only wish I knew someone with the diagnostic tool.
I agree check your grounds.

Mine did this last year and it was the alternator. The batteries would lose voltage and once they got around 11 volts the gauges would start to bounce around then the motor would run rough and finally die.
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