Low power, Broken spark plug

E

emckissack@hotmail.com

Member
May 21, 2016
134
Pensacola
Boat Info
240 Sundancer 2007
Engines
5.0 Bravo 3
Hi there,

Been working on the boat, getting her ready for the season. Yesterday when idling to the boat launch, I noticed that the engine was running a bit rough. I then realized that my max rpm was 4500 wide open. Also, when loading her onto the trailer, she did not have enough power to get her all the way up to the wench. This morning I decided to pull the plugs and troubleshoot the distributor and stuff. The first plug I pulled had the side electrode broken off. My question is, How much power can one expect to lose running one cylinder down. I have an 07 Mercruiser 5.0. I have pulled my other plugs and they all look real good except for the last 2 that are going to be a PITA to get to. Do you think replacing just the one broken plug will restore my power issue?
 
Wonder if it possible the previous owner considered and did just that? Gaskets are cheep. Remove the manifold if you have to.
 
I replaced all of them 2 years ago. So I found 1 more plug that was broken. I winder if I got ahold of some bad plugs?
here is a pic of them. One is from the back left manifold and the other is from the front right manifold. so 2 are bad.
 

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It would appear to me that the plugs may not be at fault but rather some other setting or combination thereof. I see the ground electrode is pretty well gone on both plugs and at least one of the plugs appears that the center electrode is burnt off as well. Other factors that could cause these problems and would be worth looking into before more serious damage results. I would take a look at the timing setting, octane and or quality of fuel being used, it looks as tho your engine is an 07 which should make it fuel injected, (very touchy systems) if you are not the original owner...has some modification been made the engine ?
 
Those look like 20 year old plugs. Not sure why they are failing like that. Agree something else is going on.
 
Yeah, those are not broken, they are worn/burnt. This can be caused by things like timing off or a lean fuel mixture or the wrong heat range spark plug.

I pulled this plug out of my engine yesterday - 3yrs old and @200hrs:
IMG_1794.JPG
 
So here are the plugs that I have out so far. I have never really had any problems with the motor until now. engine has 500 Hrs on it, I have put 150 of those on her over the past 3.5 years. Gonna borescope it tomorrow and see if there is any damage.

How do I check timing? I have a timing gun if that will work. Also, how do I test for lean condition and make adjustments if needed?
 

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Im not sure you can use a timing light on a 207 engine. I havent worked on a gas motor in a long time but im thinking there is probably going to be some way to check it without plugging it up the computer. Maybe somebody with more modern gas motor experience will chime in and help out.
 
I would put a borescope in that cylinder and look around.

In regards to the timing this is the procedure but unless you have access to the Rinda or Mercruiser plug in tool....you are wasting your time. I would scope it, put new plugs in (maybe a new cap and wires) and get back to boating.

https://www.rinda.com/marine/marine.htm

EFI / MPI Models

1. Connect timing light to number 1 spark plug wire.

2. Start engine and run at 1300 rpm until it reaches normal operating temperature.

3. Stop engine and connect the scan tool or timing tool to the DLC connector on the EFI/ MPI wiring harness.

4. Start engine, allow rpm to stabilize.

NOTE: MEFI-1 models only, manually adjust remote control throttle lever to get 1200 engine rpm.

NOTE: MEFI-2 and MEFI-3 models only, ECM will automatically adjust engine rpm to approximately 1200 rpm when put in the service mode on a scan tool or when using the timing tool.

5. Check ignition timing. If incorrect, rotate the distributor until timing is correct. Torque clamping screw to 18 lb-ft (25 Nm).

6. Recheck ignition timing.

7. Disconnect scan tool or timing tool from DLC connector.

8. If required, return remote control throttle lever to idle position and shut off engine.

9. Restart engine, increase rpm to 1300 then return to idle position slowly. Ensure that engine returns to idle rpm. Readjust throttle cable, if required.

10. Shut engine off.
 
Might be worth checking the injectors to those cylinders?

Agree with above that something else is going on.
 
After doing some research online, I think your issues were caused by too little fuel. You need to find out why the engine was seeing detonation (too much spark advance, too little fuel, not enough octane...) and fix it or you'll do more damage if you only replace plugs and go

Just my opinion, not an engine guru by no means....
 
I wonder if your cool fuel module has the paint coming off inside and has clogged the injectors causing it to run lean and burning the plugs. Just a thought.
 
Thanks for all of the reply’s. If it is an injector problem, is it possible a fuel additive could help out? Any recommendations if so. I use non ethanol gas but do you think moving to premium fuel would be better?
 
I have two V6 fuel injected motors that are 19 years old with 503 hours. I just changed the spark plugs which were original to the boat. Of the 12 plugs, not a one of them was nearly as bad as those plugs you pulled.

With all the junk vehicles I have managed to keep running in my life, I have never pulled plugs so damaged.

I think you definitely have an ignition or fuel problem and not just “old” plugs.

Is it possible the plugs were changed to the wrong ones? Should you have shallow plugs instead of long plugs?

I think it would be worth your investment to consult with a trusted certified Mercruiser mechanic on this one. Just my opinion. You don’t want to blow or burn a hole in the top of a piston.
 
kevin27 said:
I wonder if your cool fuel module has the paint coming off inside and has clogged the injectors causing it to run lean and burning the plugs. Just a thought.
Click to expand...
@kevin27 may be onto something here.

A buddy had to get his fuel system purged on both engines because mercury painted the inside of the fuel system and over time it came loose. I am sure others here who have had to deal with it can explain better. I just remember my friend telling me his mechanic told him it wasnt a question of "if" it would happen, just "when"
 
That year engine def. had the CF3 paint issue. You need to service the entire fuel system, from tank to injectors. Make sure your running the correct plug for that motor.
 
Is that an MR43T plug? Doesn’t look like it.
I thought these are pretty standard in Merc engines.
Do what scoflaw says. Contact Merc and find out if that is the proper plug.
 
After looking up what a MR43T plug looks like, I would say I have the wrong plugs. Mine do look a bit longer. I hate I just spent 70 bucks on them and already installed them yesterday before I read this.
 
emckissack@hotmail.com said:
After looking up what a MR43T plug looks like, I would say I have the wrong plugs. Mine do look a bit longer. I hate I just spent 70 bucks on them and already installed them yesterday before I read this.
Click to expand...

Ahhh...Grasshopper...I learned long ago, always consult the Oracle named “CSR” before working on the boat!!
 
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