150 optimax trouble

[Ray208]

I originally posted this on a different thread and was advised it belongs here:

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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.

[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.

[lpugh]

Compression is low if it was tested correctly with an accurate gauge, must be checked with motor warm, fully charged correct battery and throttle wide open
A timing light can be used to check for spark but will not tell you if there is enough available voltage, a great quick test though

Use a KV tester to check available voltage from each coil

I think you have timing light problem, as you described, I doubt the motor would start, be sure the power and ground leads have a good connection, Some low priced timing lights will not trigger well on these motors. Your car builds a lot more voltage than your outboard to fire the plugs
Your car probably has over 12,000 volts in the secondary wires at idle and your outboard will be less than 6,000 at idle, to many variables to go into all the reasons for this here and now, just take word for that, Under a load the voltage will go up a great deal and I suspect the light will start flashing

If you are not afraid of getting bit, do as I do with the motor running run you hands over the plug wires and coils to check for leakage, You can also mist the wires with a sprayer and coils with water and watch for sparks or a change in the way it is running

Fuel and air pressures check are in order while problem is occurring also check the low pressure fuel pump as well (shrader valve for this is on the vst)
Check for fuel in the air line side by depressing the shrader with motor running

Sound like you have a misfire under load such as a coil or wire

[Ray208]

I replaced all six coils and its running good as new. Can someone tell me how to test the old coils?
I would like to keep the good ones as spares but not sure which ones are bad. They were all firing at low rpm, one or more were apparently intermittently dropping out at higher rpm.

Thanks for the help.

Ray

[lpugh]

O-scope or kv tester, OHM test may or may not find bad coils

[Ray208]

I need more detailed instruction to determine the good vs bad coils. I don’t know what an “o scope” or KV tester is or how to use those devices. The boat is running great with the new coils, so problem solved, but I really want to determine which coils were bad and keep the good ones for spares, if there is a way to determine that.

Thanks for any help-

[lpugh]

Buy a Mercury service manuel for your specific motor and you will find in the specific proceedure and specs to test them with a ohm meter, ohm testing will not always find a bad coil, with a occiloscope or kv tester you are running the motor and measureing the actual avaible voltage from the coil, by far the way to test them
A little late for that now unless you want to reinstall them and take it to a dealer

In the end depending on which coils you have, you were probably better off replacing all of them as some unit are well known for coil failures
A little tip on coil failures: A plug wire or spark plug with high resistance will force a coil to operate at a much higher voltage than normal which puts a lot stress on all insulated areas which may break down under load causing premature coil failure

Be sure the plugs are replaced at recommended intervals and plug wires are in good shape and do not have excessive resistance