HowTo: Sea Doo Running Rough? Change the Spark Plugs First

I had one of my 2006 Sea Doo RXPs out on the lake last weekend, when I noticed it was running kind of rough. The engine didn’t sound right, and it felt low on power. Every now and then, I’d get a burst of full power, but then lose it again. Those are classic signs of not running on all cylinders — and on a three cylinder craft, that’s no good.

If this same problem is happening to you, don’t drive to the Sea Doo dealer with your wallet open just yet. You can save yourself a lot of time and money by simply replacing your spark plugs. Changing the spark plugs on a Sea Doo is fast, cheap, and even if you’ve never changed a spark plug on anything ever before, you’ll be able to do this — all by yourself — by following this simple guide.

Toos & Supplies You’ll Need:

A 5/8″ spark plug socket (around $9 for a nice one, but you may already have one in your tool kit)
A ratchet and at least one socket extender (you probably already have this in your toolbox)
Some dielectric grease or compound ($8 for a tube that will last you a long time)
Some anti-seize lubricant ($8 for a bottle that will last you a really long time)
OEM-recomended spark plugs (mine were under $3 each at a local auto parts store)
A spark plug gapping tool ($1-2 at a local parts store)
A shop rag

As far as the spark plug wrench or socket goes, you may already have one in your tool box, and hopefully it’s the right size. Spark plugs are either 13/16″ or 5/8″. On the 2006 Sea Doo RXP (and probably most other Sea Doos), you’ll need a 5/8″ socket. You can find them sockets for on Amazon, and if you’re feeling really fancy, you can even opt for one that’s magnetic.

Because the spark plugs are down inside the engine block, you’ll need an extended spark plug socket, and/or a socket extender on your ratchet. I use a standard size socket with an extender.

Any hardware or auto parts store will have dielectric grease. I’m a fan of Permatex brand. It’s especially useful in watercraft applications, as it helps prevent electrical connections from corroding. You can buy a large tube, or individual use packets. I like to be generous with the stuff, and it stores for a long time, so a large tube isn’t a bad idea. You may want to try some Dow Molykote (also called Compound 111). It’s a grey substance that’s thicker than dielectric grease, but serves the same purpose. BRP uses it at the factory on the rubber spark plug caps (you’ll see it when you take the caps off to access the plugs).

Anti-seize lubricant is also a must. It’s about $16 for a large bottle on Amazon, but you can use it on lots of stuff, and it lasts forever. Any time you’re joining two pieces of metal that you’ll later want to un-join, and especially if they are made of two different metals (like screwing a steel spark plug into an aluminum Sea Doo engine block), you need to use this stuff.

As far as which spark plugs to get, you’ll hear a lot of advice about iridium plugs, or high-tech blah blah plugs. But the truth is that the cheapo OEM-recommended plugs work the best, last just as long as any of the exotic plugs, and are a fraction of the price. Any of the Sea Doo 4-tec engines (on the RXP, RXT, GTI, or GTX) use the NGK DCPR8E plugs (also referred to as NGK part 4339). They’re about $3.70 each on Amazon (which is so cheap that they’re only available as an “add-on” item if you’re ordering something else, since shipping would be more expensive than the plug). I ended up buying a box of 12 from O’Reilly Auto Parts for around $3 each. They don’t go bad, and you’ll be glad you have extra when you need them (I actually keep one in the on-board tool kit). Be careful not to buy the DCPR8E “Solid” plugs. You need the ones with the threaded cap, and you’ll need to remove that cap before you install them.

Getting Started

Once you have all your parts and tools handy, remove the seat to expose the engine bay. I’ve found this procedure is easiest if you’re on the port side of the boat. Before touching anything, make sure you don’t have a key attached to the ignition. If it makes you feel better, you can disconnect the battery, but as long as you don’t have the key attached, you’ll be fine.

First, pull out the oil dipstick and place it down somewhere clean. The dipstick is attached to the smaller yellow plastic ring handle in this photo:

Sea Doo 4-tec Engine Bay

Next, use your fingers to depress two tabs (one the left and right of the engine cover) and then pull the cover upward to remove. I like to place the cover face down on a towel on my dock when I do this, then I can store removed parts inside the cover like a dish.

Before you move on to disconnecting stuff, I recommend doing all the steps necessary to change a plug one plug at a time, and then move on to the 2nd and 3rd plugs, especially if this is your first time performing a plug change on your Sea Doo.

Remove the Rubber Spark Plug Cap / Ignition Coil

You’ll see a quick-connect attached to each of the rubber spark plug caps (also called a “coil stick” or “ignition coil”). Use your thumb to release the connector, pull it out of the spark plug cap, and move it out of the way. Grab the top of the rubber cap and rotate it back and forth while also pulling upwards. It should pull out without much resistance. Carefully set it down somewhere clean (inside the engine cover works for me).

FYI – if any of the rubber pieces are worn and/or need replacing, the part numbers you need are 420664020 for the whole ignition coil assembly and 420460830 for just the rubber boot / sealing cup.

Remove the Old Spark Plug

There’s actually a proper sized spark plug wrench in your on-board tool kit which will work, but I find it easier to use a ratchet and socket, especially if you encounter resistance. Use your 5/8″ spark plug socket and ratchet to apply gentle counter-clockwise pressure to unscrew the spark plug (remember: righty-tighty, lefty-loosey). The plug should remove rather easily, but if the current set of plugs weren’t installed using anti-seize lubricant, there could be a fair amount of resistance. It’s OK to push/pull your ratchet handle with some smooth force, but be very careful not to apply too much force. The plug threads are made of steel, while the engine block is softer aluminum, so don’t damage your block by cranking away on a stuck plug. If it’s really stuck, auto parts stores sell a product called PB Blaster that you can spray down the hole, wait a while while it loosens things, and then give it another go. If it’s still too hard to remove, your best bet is to take it to the shop, which is cheaper than a damaged engine block.

Here’s what my engine looked like while removing the plugs:

Sea Doo RXP Spark Plug Removal

Once the plug is loosened all the way, you can use the rubber spark plug cap to press down in the hole, grab the top of the plug, and pull it out. The bottom of the plug will probably appear dark, and when it’s too dark that’s called being “fouled.” Here’s what a well used plug looks like once removed:

Fouled DCPR8E Spark Plug

Throw away your old plugs one they’re removed.

Prepare the New Spark Plug

To prepare your new spark plug for installation, you’ll need to do three things:

Remove the threaded cap
Set the proper gap
Coat the large threads with anti-seize lubricant

Removing the small silver threaded cap on top of the plug is easy. If it doesn’t just come off by hand, you can use one or two sets of pliers to help do the job. Discard the small metal cap, leaving just the exposed threaded post.

Next, your DCPR8E spark plugs should be gapped to a width of approximately .030 (inches). Out of the box, the gaps on mine were too small. Grab your spark plug gapping tool and slide the smallest part of the tool into the gap, then rotate the tool until the prong is at the .030 position. If your gap was too wide to start with, gently press down on the bottom end of the plug to reduce the gap, then use the gapping tool to set the proper width.

The final plug prep step is to evenly apply a coat of anti-seize lubricant to the larger bottom threads (not the smaller threaded post up top) to make them easy to remove the next time you need to change them. Make sure the threads are covered, but don’t go crazy and use too much. A nice, thin, even coat works best.

Install the New Plug

To help put the new plug down into the engine block, use the rubber spark plug cap to “grab” the top of the plug and lower it down into the hole, give it a couple gentle turns to start it threading, pull out the rubber cap, then use your spark plug wrench to tighten the rest of the way. I like to initially tighten just past “snug” to crush the spark plug washer, back it out a bit, and then re-tighten it down all the way to seat it properly. The factory spec torque is 17 ft-lbs, but I don’t use a torque wrench. Just make sure they’re in nice and tight, without over-doing it. You are going to want to get these out again some day.

Grease and Re-Install the Spark Plug Cap

Break out your dielectric grease or compound, and apply liberally to the top part of the rubber spark plug cap’s shaft, as shown here (credit to Dr. Doo on Sea-Doo.com):

Put dielectric grease on the rubber shaft

This helps seal out water and gunk from getting down into the spark plug hole. You should also apply a glob on the bottom of the cap, inside the hole that covers and connects to the spark plug.

Push the spark plug cap back down into the hole, on top of the new spark plug. Wiggle it gently back down into place, and then turn it so the connector is facing the right way. Put another dab of dielectric grease on female side of the connector, and reconnect the wire.

Replace the Engine Cover and Dip Stick

Once you’ve repeated the above steps and replaced all three plugs, replace the engine cover by snapping it down into position, wipe any debris from the dipstick with a shop rag, then re-insert it into the engine. Replace the seat, and you’re done!

Go for a Test Ride

Now all that’s left is to take your baby out on the water, warm it up a bit, then open it up wide. You should have full power with all three cylinders firing strong. You’ll also have a huge grin on your face, knowing you now know how to fix the #1 most common cause of PWC misfires and loss of power — at a fraction of the cost the shop would have charged you.

And the next time your Sea Doo engine starts running rough, you’ll know exactly what to do, and you’ll probably able to do it in half the time.

If you have suggestions, feedback, or questions, please leave them in the comments below. And I invite you to check out my other Sea Doo related posts while you’re here!