Center Electrode burned away

[Chris1956]

Folks, I started my '88 4.3LX, and it ran poorly. Just for fun I pulled the spark plugs I had installed last summer and looked them over. Several had rounded electrode straps, and one was missing at least 3/16 of its center electrode. It appeared to be burned away. I replaced them, and the motor runs much better. Now for the ?? Last summer I mistakenly installed AC R43TS6 (Automotive) spark plugs, instead of the correct MR43T Marine plugs. Is that why the straps burned away and the center electrode was burned away? Did I do any harm to the motor? What are the differences in the plugs? I showed the "bad" plug to a local mechanic, and he acted like he had never seen one like it. He also suggested I do a compression check (it was 150PSI, which I think is OK), and maybe water is getting into the cylinder. Any other suggestions?

 

[Don S]

Re: Center Electrode burned away

Doesn't sound like water, sounds more like you are possibly running it too lean or the timing is off.<br />I'd sure put in the proper plugs, recheck timing and make sure the advance timing is also working, adjust the carb and see what it does.

 

[chuckz]

Re: Center Electrode burned away

I'm not sure about the difference between marine and automotive plugs, but normally a burned electrode indicates a lean mixture. Check that the carburator and make sure the mixture is adjusted properly.<br /><br />(EDIT) Well I see Don types faster than I do.

 

[Chris1956]

Re: Center Electrode burned away

Don and Chuck, Thanks for the info. I also replaced the Ignition module on that motor last season and and have experienced pinging at high speed, ever since. I upgraded to mid-grade gas and kept the speed down to avoid the pinging. I also retarded the idle (static) timing advance from 6 degrees BTDC to 4 degrees BTDC. This helped a bit. I plan to try it this year and if it still pings, I will retard to 2 and then zero degrees if necessary. Since I purchased the ignition module at a Mercruiser dealer, I presume I received the correct one.

 

[Mahoney]

Re: Center Electrode burned away

sounds like your engine is advancing spark to much at higher rpm's which will definitely lead to hot plugs. Check your manual for total advance and shoot the timing. If your advance is too far off, you may not even be able to compensate using static timing, which is severly reducing your efficiency at idle and lower RPM's anyhow. You would be just covering up the problem, causeing issues in other areas.<br /><br />you could have broke a spring in the mechanical advance mechanism causing the wieghts to swing out way to fast.

 

[Chris1956]

Re: Center Electrode burned away

Mahoney and others, The distributor does not have a mechanical or vacuum advance. Timing advance is done by the Thunderbolt Ignition module. I do not have a better plan than to back off the static timing until the pinging is under control. <br /><br />Question: Will the motor run great at high speed if the mains are partially clogged? Would this account for the pinging?

 

[Mahoney]

Re: Center Electrode burned away

I am not farmiliar with the thunderbolt module, but you should contact them on your issue. Simply changing the static timing is not the correct way to address the issue. It says this in a manual I found online.<br /><br />are you sure you have a module for a V6 and not a v8?

 

[Bondo]

Re: Center Electrode burned away

Just for fun I pulled the spark plugs I had installed last summer and looked them over. Several had rounded electrode straps, and one was missing at least 3/16 of its center electrode. It appeared to be burned away. I also replaced the Ignition module on that motor last season and have experienced pinging at high speed, ever since. Question: Will the motor run great at high speed if the mains are partially clogged? Would this account for the pinging? <br />

It's a Wonder that you Even have an engine to Work On,...... You're Detonating this motor Badly,..... I'd be Surprized if you don't have Craters on the Top of your Pistons........ <br />You've Got to Get This Under Control..........<br /><br />Does this have the Little Small Ignition Module mounted on the aluminum plate,........ Or the Box Type,???? <br /><br />If it's the Little Module,.. The Advance is Stamped into the face of it......Right by the Plug...........<br /><br />If the Carb. is running Lean,... Yes, It Could Also be a Big Part of your Issues.....<br /><br />A Slightly Lean Carb.,+ your Timing Issues,....You're Blowing the Best Parts of your engine Right Out the Exhaust...........

 

[Chris1956]

Re: Center Electrode burned away

Bondo, My motor has a small Sensor module inside the distributor. It has two studs which stick through the Dist. housing, which connect to both the ignition coil and the ignition amplifier.<br /><br />Unfortunately, I do not know how to check max advance, since the engine only has a timing indicator plate which will indicate 10-12 degrees BTDC maximum.<br /><br />I will also clean the main jets on the carb to be sure.<br /><br />Thanks for the info.

 

[Lou C]

Re: Center Electrode burned away

Timing total advance can be checked with a timing light that allows you to dial in the degrees of advance on the timing light, then run the motor at the specified RPM and you can see if it is right. To do this the boat should be in the water, you really can't run a motor on the hose at 3000 rpm!

 

[jeff13601]

Re: Center Electrode burned away

vipzak put a web add in my last post that explains why plugs do what very thoroughly

 

[Bondo]

Re: Center Electrode burned away

With a T-Bolt IV,..the Advance is built Into the "the ignition amplifier".............<br /><br />Where is your "ignition amplifier" mounted,..... What's it Look Like.....<br /><br />So You're saying, you replaced the Senser, Inside the Dist. ?? Not the Module mounted Outside the Dist.????<br /><br />Either Way,.... Don't Keep Running It the Way It Is..............<br />My 1st Guess is You Should go back to where the Issue Started,+ See What Got Screwed Up.........<br />Something Is Very Wrong........

 

[Chris1956]

Re: Center Electrode burned away

Bondo, The Ignition Amplifier is mounted on the inside of the exhaust Manifold. It is aprox. 4" x 4" x 1.5" box with heat sink fins. It is original. The component I replaced mounts in the base of the distributor, near the reluctor. I will check part numbers to see if I was sold the correct module. If you have a method to adjust the advance, I am all ears!

 

[Bondo]

Re: Center Electrode burned away

If you have a method to adjust the advance,

If you Changed the Pick up Senser, then the over all timimg Advance shouldn't have changed,... it's controled by the Box on the manifold.....<br /><br />I'd Still think you've got to go back to When you changed the part you Did,+ See What you Screwed Up..........<br />It was OK, Before you Fixed it,+ Since that time it's been Wrong...... So, Go back to Where/When things Changed......

 

[Don S]

Re: Center Electrode burned away

The Ignition Amplifier is mounted on the inside of the exhaust Manifold.

No wonder it doesn't work, they won't live INSIDE the manifold !!!!! <br /><br />Seriously, the exhaust amplifier is what controls the timing. Be sure you have the wires hooked up properly on the distributor.<br />Also check the small harness where it plugs into the ign. amplifier. If it's corrode, it should be replaced, also check the amplifier itself. I've seen many of them without advance have one of the termanils corroded off completely.

 

[Chris1956]

Re: Center Electrode burned away

Don, The ignition amplifier is the old style without a connector. The wires appear to be in good condition. <br /><br />The Ignition pickup module faces the stern, with the two connector studs sticking out the rear of the distributor. I have two White/green wires on the starboard connector stud of the ignition pickup, and a single white/red wire on the port connector stud. Since my Seloc manual is not specific, is this correct? Is there a correct connection point, or with either work?<br /><br />Also, the purple wires are on the + side of the ignition coil, and grey on the negative side of the ignition coil. This matches the wiring diagram in my manual.

 

[Don S]

Re: Center Electrode burned away

Here is the wiring diagram for the TB IV ignition, it's for a V8, but is the same as a V6.<br />Sounds like you have it right, you just need to check if you have advance timing.<br />Start the engine, with a timing light verify where the timing is. Then run the engine rpm up to 3000 rpm and see how far the mark moves from the original setting and let us know that distance. It doesn't have to be in degrees.<br /><br />