Proper spark plug gap for Mercruiser 350 Black Scorpion

[rjh171]

Hi all,

I'm looking to confirm spark plug gap for a 2002 Mercruiser 350 Black Scorpion. My manual states the plugs need a gap of 0.045, but the cover over the ECM states the plugs need a gap of 0.030. The plugs I removed, which have been in place for a number of years, have a gap of 0.045, and the engine ran fine. My concern is that I'm fighting an issue with loss of power when under load, and I'm trying to rule out any possible issue. Items I've addressed thus far are as follows:
- Complete drain of fuel tank as a result of replacing the steering cable; fresh gas with Seafoam treatment
- Replacement of in line fuel filter and fuel/water separator (part of annual maintenance along with change out of engine oil/filter and v-drive and transmission oils and raw water pump impeller)
- Replacement of fuel line between fuel tank and fuel/water separator
- Replacement of spark plugs, wires, distributor cap, and rotor; firing order verified to be correct (quadruple checked); had heavy corrosion inside distributor

After all of the above, power is still cutting out when under load. The cut out varies between 2,000 and 3,000 RPM, but occurs every time when hitting this RPM range. When pulling back on the throttle, the engine recovers most of the time. A few items it will either have a minor backfire, bog down and die (can immediately restart), or will begin to rev back up. The battery, while a few years old, has consistently been charged and shows just under 13 volts when connected to the voltmeter. The spark plugs showed some signs of wet fouling appearing to be gas and not oil indicating the engine is running too rich on fuel or too lean on air. No known ECM codes, but I will be checking the ECM this weekend. No signs of debris in the flame arrestor; however, there were some carbon / black dust deposits. I plan to remove the IAC and clean/inspect. I also plan to check the fuel pressure for proper operation of the fuel pump. Any other areas to look at prior to throwing in the towel and taking it to a professional?

Thanks,

Joe

[bighitst]

Having the same issue here, no simple solution

Hi all,



I'm looking to confirm spark plug gap for a 2002 Mercruiser 350 Black Scorpion. My manual states the plugs need a gap of 0.045, but the cover over the ECM states the plugs need a gap of 0.030. The plugs I removed, which have been in place for a number of years, have a gap of 0.045, and the engine ran fine. My concern is that I'm fighting an issue with loss of power when under load, and I'm trying to rule out any possible issue. Items I've addressed thus far are as follows:
- Complete drain of fuel tank as a result of replacing the steering cable; fresh gas with Seafoam treatment
- Replacement of in line fuel filter and fuel/water separator (part of annual maintenance along with change out of engine oil/filter and v-drive and transmission oils and raw water pump impeller)
- Replacement of fuel line between fuel tank and fuel/water separator
- Replacement of spark plugs, wires, distributor cap, and rotor; firing order verified to be correct (quadruple checked); had heavy corrosion inside distributor

After all of the above, power is still cutting out when under load. The cut out varies between 2,000 and 3,000 RPM, but occurs every time when hitting this RPM range. When pulling back on the throttle, the engine recovers most of the time. A few items it will either have a minor backfire, bog down and die (can immediately restart), or will begin to rev back up. The battery, while a few years old, has consistently been charged and shows just under 13 volts when connected to the voltmeter. The spark plugs showed some signs of wet fouling appearing to be gas and not oil indicating the engine is running too rich on fuel or too lean on air. No known ECM codes, but I will be checking the ECM this weekend. No signs of debris in the flame arrestor; however, there were some carbon / black dust deposits. I plan to remove the IAC and clean/inspect. I also plan to check the fuel pressure for proper operation of the fuel pump. Any other areas to look at prior to throwing in the towel and taking it to a professional?

Thanks,

Joe

Same thing here:
I am having the same issue. I have the manual and it tells you to check the following:
1.to much oil in crankcase, 2. anti siphon valve, 3. plugged fuel vent 4. improper Fuel supply 5. incorrect ignition timing 6 low grade fuel/water in fuel 7 spark plugs/wires 8 distributor/rotor 9 coil 10 engine overheat 11 low compression 12 exhaust restricted.
The gap is .045 for your plugs.

Good Luck

[rjh171]

I'm guessing we have the same manual as I've checked most of these. Thanks for the feedback on the gap.
1. Ruled out as 5.5 quarts of oil drained out and 5.5 quarts of oil added back. Oil still looks news.
2. Checked it when replacing the fuel lines; functioned correctly
3. Possible, but not probable. If not paying attention when filling with gas and filling too fast, the fuel vent has spewed out gas. Can see the vapors as well when filling up the tank.
4. Possible which is why I'm checking the fuel pressure.
5. Possible but haven't gone down this trail yet.
6. Ruled out after having emptied the fuel tank and lines.
7. Replaced.
8. Replaced.
9. Possible and haven't looked at this yet.
10. Unless the temp gauge is broken, not likely.
11. Possible and haven't checked.
12. Looked in from the outlet and haven't seen any restrictions.

Thanks,

Joe