Weird idle/fuel issue looking for ideas on where you would start.

[jerms01]

Ideas Please: 98 Nitro 884 Merc 150 efi. The last couple of trips the idle has been a bit rough. Was at the lake yesterday all seemed well. Took a really long run around the lake at WOT then found a spot to fish. Fished for maybe an hour then tried to move. I could no longer get the boat to idle it would just die. I could take it out of gear rev it up and keep the RPMs at or above 1000 and it seemed fine. Put the shifter back in park and it would die. Well it was the end of the trip and the ramp was right there so we packed up and left, too damn hot out here in AZ. Get home and it fires right up and idles (700rpms) with no issues. Just replaced the fuel lines about a month ago gonna and didn't really see an inline filter. Just the separator not sure if this also handles the filtering but gonna swap it out. May adjust the idle screw to keep it closer to that 1000 rpm range. Anything else I should be looking at? TIA

[pipeliner87]

I just went through almost the same thing. I checked the spark plugs and made sure the coils were hitting. I also checked the compression in each cylinder (just to be sure). I unhooked the gas line where I could pump some into a bottle to make sure I didn't have water or anything getting to the carb. I put a new fuel filter/ separator on. I had to tighten the little brass check vale thing that is on top of the tank that your gas line hooks to (the line with your bulb). I also had to put a hose clamp on that same line. I changed the lower unit oil (which was 80% water FML). Now, I am no mechanic by any means and was about ready to call mine. But one of those things fixed mine for now. Hope you get it running right. I love my 884.

[jerms01]

Thank you sir! I am going to run through the fuel system today and replace the separator. Best of luck with your LU bud. Love my 884 as well its been a work horse gotta keep it going for a couple more years at least haha

[jerms01]

Ok guys could really use some input. I have never tried this before and am not exactly sure what I should be experiencing when pulling plug wire at idle. I have taken a part the VST and cleaned the screen and tested fuel pressure which seems ok at 36 or so. Gonna retest this weekend as the tester I was using sucked. Anyways here is a video of my tests. 3 plugs when disconnected cause the engine to stop completely the other 3 there is little to no change. Any advice on what you would do next is greatly appreciated.

[berudd]

You have a idle issue and you pull one plug wire that would indicate the coil is bad. This is what my mechanic told me when one of mine went out. He used the computer to shut them down on by one. Each time the engine would run worse except for the cylinder with bad coil. There was no change when he shut that one off. He said I could do it by pulling the plug wire. Almost seems like you've got three that are bad. Try this. Swap the coils between the top two cylinders on the right side (where you started) If the problem follows the coils, I would suspect a problem with them.

Would be odd if three were bad all at once but you might have had them going bad (or some gone) for a while and it only now got so bad you noticed it. How do the plugs look on the suspected bad coils? Mine was blacker than the rest. Also, I don't think a coil is ether 100% good or 0% bad. Mine was still good enough to fire a timing light but not strong enough for the motor to run correctly.

[berudd]

If you post this in the Mercury forum then you'll be able to get some expert advice.