Spark Plug Boots on 91 120HP Force

[ebjr]

First let me say that I've been browsing through these forums for some time now and have found a wealth of knowledge on here. This is a very informative site, especially for a newbie like me.

Now to my issue.
Went out saturday afternoon and shortly after getting out of the "idle wake" zone we get on the gas and almost instantly notice that the somethings not right. the motor sounded like it was firing properly. the motor wasn't knocking or anything but it would lose a little power every few seconds, almost like it was hesitating. We were still able to cruise around 35mph. We didn't notice the issue when going at slower speeds.
So we get the boat back home and started checking the simple things, looking for loose wires, checking the pugs and water separator. It didn't take long to find the problem. The top spark plug wire just about came off on its own when I went to check the spark plug. The top of the spark plug was brown and the inside of the boot itself was filthy. The spark plugs are less than 2mo and the other 3 looked nice and clean and the boots were perfect as well. Also, the back part of the boot that attached to the wire had a bunch of black gunk oozing out when you pinch it.
So now the question is can we just replace the boot or do we need to replace the entire wire/coil set?

I appreciate any advice. Thanks! Ed

 

[Dave K.]

Re: Spark Plug Boots on 91 120HP Force

Hello Ed & welcome to the site. Yes, you can just replace the SP Tips. I have a 85hp & a couple of years ago noticed one boot was broken at the elbow & the plug was arcing. I replace all three boots - just cut the plug wire & trim so a little wire is showing & use a little vasaline to insert the wire into the new boot - very easy!

Now I'm assuming your 90 is the same set up as my 85

 

[kandil]

Re: Spark Plug Boots on 91 120HP Force

I would buy new wire and boots from the Mercury dealer it cost about $6

 

[roadrunnr]

Re: Spark Plug Boots on 91 120HP Force

Ed:
As Dave says spark plug boots are easy to replace and are also available here on iboats. The wires are part of the coil and cannot be replaced. I don't know how others have done this but when I replaced mine on my 85 hp I lightly sprayed the wire with WD40 for ease of installing the boot. Good luck and let us know if this corrects your problem.

 

[john from md]

Re: Spark Plug Boots on 91 120HP Force

Sometimes the plug connector is so corroded that you need to replace it.

One way I found that works is this.

I went to the hardware store and bought some springs that fit on the top connection of the spark plug. I then cut the connectors off of the wires, removed the boots and replaced them. Then I cut the springs to about 1/2 inch long and bent one of the ends out a little. I then pushed this end through the spark plug wire and bent it over. I coated it with marine teflon grease and inserted on the plug.

My latest engine has had all three plug wires modified like this and it runs like a champ for the last two years.

Regards,

John

 

[kandil]

Re: Spark Plug Boots on 91 120HP Force

I have a 94 and if the 91 is the same as the 94 you can buy the wire and boots and it comes off at the coil.The wires are not a part of the coil on mine.post a photo of the coil if you want

 

[roadrunnr]

Re: Spark Plug Boots on 91 120HP Force

Ed:
I checked on mercruiserparts.com, Kandil is right, Merc did make a change over in the ignition systems on Force. From 91-94 they list two different coils, one with a seperate plug lead and one with the lead integrated with the coil. You may or may not be able to replace the high tension leads depending on the type of coil you have. It looks like from 95 on the coils have replacable leads. Sorry if I gave you misleading info, I was basing my reply on my 89. If I had replacable leads I would definitley replace them!