Help!496 Mag HO running on 6 or 7 cyl

[PUMPNSQUIRT]

1000 miles from home and don't see anything obvious.Wires,injectors,ECU connectors-all looks good.80 hours on a stock motor and just started running like crap.Any suggestions??

[PUMPNSQUIRT]

Suspect possible cam sensor or coil-any way to test these without a scan tool ??

[Raylar]

You might want to isolate which cylinders are running bad. You can start the motor and disconnect one injector at a time. If the motor runs or sounds worse after being unplugged thats not the problem cylinder. If the motor does not get worse, thats one of your bad cylinders. Be carefull to pull out the green plastic clip from the injector connectors before you pull off the connector!
You should check some obvious things first to make sure the engine is safe to run. First check oil for water in oil. Make sure oil pressure is still close to normal. Look for loose or damaged plug wires. Check for coolant in heat exchanger. Check for drive oil in lube bottle. Check to make sure raw water pump is pumping water. You can check this on the trailer with a hose flush hookup.
Remember the computer on this engine will cut the power levels by as much as 90% if the sensors on these systems are showing a problem. If you are able to determine that you have a problem cylinder, remove the sparkplug and check the compression in that cylinder, also look at the plug to see if you see water or heavy oil on it. Don't assume the problems real bad until you know what the problem is! If all of this is to much for your mechanical skills or it scares the hell out of you, see a good marine mechanic with a Merc scan tool! Hope this is some help, sorry for your problems, I hope they are minor.
Raylar:wink:

[PUMPNSQUIRT]

Thanks Raylar - have done most of the above with the exception of the cyl isolation and compression test-plugs look ok and since it started all at once I believe it's prob a coil.I'll try removing connectors one at a tome to confirm.Thanks for the help.

[bordsmnj]

had a loose connection to ground at the battery terminal once with a new merc efi motor. the computer went nuts and started doing all kinds of stuff. 2 dollar part killing the 300 dollar part:( luckily merc really good about their warentees.:D my total cost was 0 dollars. i'd take it to the nearsest merc mechanic(or call) and see what they have to say. threr's always the chance that they'll take care of yuh on the spot. it's been done before. good luck -jas