Optimax 150 troubleshooting

[Ray208]

SN: 1B539810
402 hours
2007 150 Optimax

I purchased the boat last fall used it for about 10 hours run time, no issues. Ran great max RMP 5600.

Over the winter I replaced the water pump, lower unit lube, belt, air filter, plugs (NGK IZFR5G) gapped at .032, and ignition wires (Sierra 18-28086).

Went in this spring and when cruising at 4200 rmp I would have a rpm fluctuation. Dropped about 300-400 rpm for a second and would jump right back up.
Second trip did the same, but this time I noticed intermittent missing at idle too.
Third trip the surging stopped but I have a general loss of power, max rpm 4600.

I suspected fuel starvation so I pulled off the water separator and it was clean. I replaced the filter with a new one as a precaution. I tested the spark at idle and in gear at the dock up to 1600 rpm and it is steady.

I pulled off the VST suspecting a clogged screen and the screen and entire tank interior was clean as a whistle.

I replaced the plugs suspecting a bad one, no improvement. The ones that came out were carbon coated and the insulators had a weird pattern - half white and half black (carbon coated).

I tested the rail pressures and I'm at 82 air and 92 fuel.

The engine starts on the first crank with no surging.

I was going to check compression today and maybe put the old wires back on thinking maybe the new ones are defective?

If compression is good I was thinking maybe the coils are acting up under load and was going to replace them. The current coils have the following numbers on them:

1045-8M0047457
2078-883778
2380-8M0042381

I appreciate any help, I'm Stumped!

Ray

[Ray208]

I also ran the engine from a remote tank to eliminate the collapsing fuel line and bad fuel theories with no improvement.

[SilverFox579]

Welcome to BBC Ray. What jumped out at me was Sierra wires, if it were mine, I'd put the OEM wires back on before troubleshooting further. Other than new plugs, that's the only thing I see that's changed and could possibly relate to your current issue. Not to imply something new hasn't cropped up, which could be.

Speaking of plugs, did you use a wire gauge gapping tool (very important) when setting gap and nothing between center and side electrode to adjust gap?

Btw, there's a dedicated forum for covering your engine just below this one, 2.0/2.4/2.5L, and is best place to post. Be sure to check out the FAQ at top of that forum, LOTS of great Optimax info there (and in the 3L forum too).

Good on you for including serial number as the pros here will need it.

[Ray208]

So I went down today and put the old oem ignition wires back on, reading how delicate the spark plugs are to pressure exerted from improper gap, I also went ahead and installed a new set of plugs and adjusted the gap to .033 with the utmost of care.
While the plugs were out I ran a compression test and all 6 cylinders were between 80 and 90 psi. Started her up and she ran very smooth. Took her out for a run and immediately the RPM began to fluctuate once on plane (4000 RPM). I didnt want to foul the plugs again so I went back in and shut her down.

Once back at the dock, I hooked up a timing light to each ignition wire and didnt get any flashing (one or two intermittent flashes, but nothing more). I checked all 6 cylinders and it was the same throughout. I thought the light was broken so I went up and checked it on my car and it worked fine. Back down to the boat and no flashing. I'm thinking its the coils now. If they are weak would that result in no flashing with the timing light???

Ray

[Ray208]

plug.jpg
Here is a picture of the plug that came out. It was only in for maybe 2 hours run time. They all look like this. The pattern on the insulator looks weird to me.

[bigoilman]

Resurrecting this old thread. Did you ever get this resolved? I'm chasing a similar symptom and have tried the same things so far.

[SilverFox579]

Resurrecting this old thread. Did you ever get this resolved? I'm chasing a similar symptom and have tried the same things so far.

Best to open a new topic for your engine, including engine serial number (required when posting), in the appropriate forum to prevent post hijacking. If you have a 135/150/175 Optimax this is correct forum for your engine - Mercury - 2.0/ 2.4/ 2.5 Liter High Performance

[bigoilman]

Best to open a new topic for your engine, including engine serial number (required when posting), in the appropriate forum to prevent post hijacking. If you have a 135/150/175 Optimax this is correct forum for your engine - Mercury - 2.0/ 2.4/ 2.5 Liter High Performance

Will do. Just seemed redundant to start all over with the same info.

[silvertalon]

While reading thru your postings I was thinking coil or coil driver. The timing light verify's that IMO. Swap around a coil to see if the problem moves to be sure. Try to find a wiring diagram showing which driver fires which coil. It can be confusing if you don't know. Or, replace them all ($$). Run (mix), quicksilver quik kleen or comparable in your fuel to combat deposits on your plugs.