2006 175 optimax seems to be dropping a cylinder under load

**Fishinmymission** · 08-11-2018, 01:36 PM

Engine has been flawless all year. Yesterday I was moving at about 4600 rpm and all the sudden. Mid trip rpms were occasionally dropping to about 4000 rpm then back. Boat was very jerky when this was occuring. Issue has not shown at lower rpms yet about 3000rpm or lower.
Any ideas I don't have a copy of my manual on my phone.
Hoping it's a coil.
Any tips on how to do the diagnosis?

**flabum1017** · 08-11-2018, 02:52 PM

start out with a spark checker, should be able to jump a 1/2" air gap. Then you will need to break out the ohm meter and test the coils. I don't have the info in front of me, so I can't tell you what the values should be, but they should all be within a hundred ohms of eachother.

You could also have an injector problem as well.

**Motv18** · 08-11-2018, 06:55 PM

Does it sound or feel like a miss; or just feel sound more like it just drops out power.

One I would start injectors or spark the other fuel supply.

**Fishinmymission** · 08-11-2018, 07:11 PM

It's not a single miss. It drops for a second or two and then comes back. The boat accelerates and deaccelerates hard while it's cycling. Then it returns to full rpms for 30 seconds then fluctuates again for another 5 seconds. That's the best way to describe it but it's random

**Fishinmymission** · 08-13-2018, 12:11 PM

I drove it again on Sunday. Issue has not yet occured below 3000 rpm. The issue does not occur often enough for me to figure out how to diagnose it yet.
Again on sunday was cruisng at 4600 rpm for 10 minutes and then hard drop in in rpms and regains it. It will do this 1 to 5 times in a 5 second period then will drive smooth again for another 2 to 5 minutes at normal rpms and then fluctuate again.
The fluctuations are usually so fast the rpms dont really bottom out to a stable number but occasionally it drops for a full second or two from 4600 rpm to a stable 4000 rpm.
Seems like Im losing a cylinder but not sure how to diagnose which one and whether it is a coil or injector.
Of course in the back of my head I feel like I'm playing a dangerous game if it ends up being an injector that is momentarily sticking closed.

**flabum1017** · 08-13-2018, 03:49 PM

could be a tps.... might need to get it scanned

**Fishinmymission** · 08-13-2018, 04:57 PM

I have vessel view mobile and have no codes. Not sure if professional scanner can learn anything else.

**XstreamVking** · 08-13-2018, 05:13 PM

You have coil issues. Replace them all. Merc had a recall on them and may help. I have swapped them on two 06 175XS's and merc helped out the customer.

**Fishinmymission** · 08-13-2018, 05:44 PM

Thanks Vking. a little more reading shows quite a few people experiencing the same intermittent symptom as me and talking about the coil recall which ended in 2015. I'm going to probably end up wasting my time and start swapping them out till i find which one it is as I just can't quite justify dropping $600 on it yet. If they lasted 12 years (and 900 hours) I'm hoping they all don't crap out at once. When the second or third one goes maybe ill smarten up.

Or is there a benefit to replacing them all such as more uniform or stronger spark?

**XstreamVking** · 08-13-2018, 07:47 PM

From my understanding a bad coil can take another out. They also can go bad to the point they blow the fuse for the power supply. I am no real tech, just learning from experience as I go and work on a few friends motors as well as my own. I have seen the coils on line for less than the dealer charges.

**hsbob** · 08-14-2018, 09:50 PM

if not coils look at the plugs. they can fail under hi rpm [load]

**Fishinmymission** · 08-15-2018, 02:49 PM

Thanks. I'm going to check for any arcing at night at idle to make sure its not a wire/boot issue. Then Ill bring my timing light with me on the boat to diagnose when it starts acting up. I bought the coil already but this seems like the easiest way to diagnose it rather than installing it up to 6 times.
If that doesn't work new plugs. These ones were new this spring and have to have under 50 hours on them.

**XstreamVking** · 08-17-2018, 03:33 PM

Might inspect your plug wires too. I found one on my 225 opti was arcing by checking them at night.

**Fishinmymission** · 10-02-2018, 05:59 PM

So been ignoring the issue and it doesn't even seem to occur when temp outside is below 70F. But its def getting worse because it only use to happen on 80F+ days.
Should i unplug the wires to the air injector or the lead going into each coil from the driver? I figure ill ride on 6 cylinders till it heats up and starts to fluctuate then I'll deactivate a cylinder at a time until i can find the culprit.

**Motv18** · 10-02-2018, 07:02 PM

Oil goes in the standard way so you’ll load up the cylinder with oil. May or may not hurt.

Unclip the coil coil might be better

running on 5 shouldn’t hurt it but no garuntee it would fail.

Check for a lose ground or hot. If all the plugs look the same. May be hitting a wave just right and nocking something lose.

Opti have several things that that can cause the same symptoms to show.