Spark plug issues.

[erie_guy]

My 1997 VP 5.7 l GI engines needed a tuneup this season and as a first step I decided to first change the sparkplugs. They have 540 hours on them and I do not know when they were last changed.

The port engine had plugs that were light tan in color and had no other deposits. However, the center electrode on two of the AC 43 plugs was worn below the ceramic insulator (and the gap was greater than 0.10"). The other six plugs were in fine shape with gaps that were ~0.045". My question is what could have caused the tips of these two plugs to degrade in such a manner ?

The starboard engine had plugs that were carbon coated - but not oily. This engine runs about 50 deg F colder than the port engine (according to the gauges). I am thinking this cold operation may be the problem and plan on replacing the thermostat when I winterize later this month. Hopeful this will result in hotter operation of the plugs and I will not have to change heat range of the plugs as they are a PITA to reach and change.

Neither engine uses any oil between seasonal changes and seem to have proper power and reach 4500 RPM when at WOT.

These engines have the throttle body fuel injection system and start and idle like champs. Do I have a problem that needs to be addressed ? Would replacement of distributor cap/rotor be advisable ?

Thanks for any assistance.

erie_guy
Port Clinton, OH

 

[Alpheus]

Re: Spark plug issues.

Well the one with the burned plugs and running hot sounds like its running a tad lean and the one that runs cold with carbon buildup is running rich.

50 degrees is a heck of a gap. What are the actual temps???

 

[Bondo]

Re: Spark plug issues.

Ayuh,... 1 is runnin' Rich, the other is runnin' Lean,...

Could be as simple as a fuel filter with Crud or water in it causing the Lean condition...

 

[erie_guy]

Re: Spark plug issues.

Many thanks- I will change both fuel filters. They have been installed for a couple of years but I never thought I had a water or plugging problem.

The rich engine shows about 120 deg F while the lean engine indicates 175 deg F. Surface temperatures on the exhaust manifolds and heads confirm the engines do run at different temperatures.

Because the fuel/air mixture is controlled by the engine computer, I am curious how I can make the rich engine run leaner ? or the lean one richer ?

I do appreciate your advice.

erie_guy
Port Clinton, OH

 

[Don S]

Re: Spark plug issues.

Because the fuel/air mixture is controlled by the engine computer, I am curious how I can make the rich engine run leaner ? or the lean one richer ?

First, get the thermstat changed on the rich engine, then hook up a diagnostic computer (Like This). It will tell you if the sensors in the engine are right.
Also do a fuel pressure check, low pressure can cause a lean condition.

 

[erie_guy]

Re: Spark plug issues.

OK - that is more than I can handle with my limited tools and multimeter.

A trip to the local VP shop is probably needed before I pull the boat for winter storage.


Don, thanks for the advice.

erie_guy
Port Clinton, OH