Weird weird situation Optimax 150

[miagonz85]

Hi guys,
So I went out this last weekend and started having this weird issue, I wish I could post a video I recorded for better explanation.

Motor won’t rev full rpms, yet when I tap the trim switch on the throttle (up or down) rpms raise for a second or 2, then drop back down. It’s random, sometimes I tap the trim and rpms stay up for a little longer, 30 secs, 1 min, then drop again. At WOT it won’t reach max rpms, stays around 4500, tap the trim and it bumps to 5000 then drop.
No beeps, checked batt connections for loose / corroded ground, looks good. I don’t understand how the trim has anything to do with motor rpms?! All power cables in the motor are solid, nothing loose. I don’t even have an idea of where to start troubleshooting this issue. Any input helps!

Its a 2006 Merc Optimax 150Hp

[miagonz85]

Here’s a link to video:

https://youtu.be/ha3HDmjXwsM

[Merc 2.5]

Yes I would say that's pretty off the wall rite there
Even if batt was bad seems like you would lose rpm from lack of voltage when u trim. Maybe one these guys will shed sum lite for ya. Unfortunately I'm not gonna b much help on newer motors. Gud luck

[miagonz85]

I know, this one got me. The boat has 2 batteries. I tried it on batt 1, batt 2 and both. Doesn’t make a difference.

[half fast]

What ever it is ,seems electrical . How old all the spark plugs ? Along those years we had some coil issues . I'de buy a coil and one at a time substitute the new one in all cylinders to see if you have one failing on you. If you have a digital temp gun you may be able to check the temp of the coils or the temp of the spark plugs and find one much cooler than the rest and narrow it down that way. Dump a little air off the air Schrader valve on the fuel rail and make sure no fuel is present . hf...

[miagonz85]

The spark plugs are new, not the coils. It also has a new alternator. The bottom coils did get wet at one point and missed fired, I dried them up with a rag while out in the water and it cleared up, ran fine after. But how will the trim switch interact with the coils?

[FMP]

A wet coil leaking may indicate a break. Wouldn't think they're related. But a drop in voltage or extra trim motor load is helping rpm. Regulator out of range causing a reduced power mode until the trim brings it back down into range or the like? That isn't a throttle by wire vs cable?

[miagonz85]

Throttle is by cable

[XstreamVking]

Try the trim switch back on the cowl. Does it do the same? If not I would say you might have a problem under the console (different power feed) maybe key switch feeding current back to motor on kill circuit? Just a guess. It is a new one on the list of opti weirdness. Just guessing....

[vnemous]

Does the battery cable from engine to battery switch lie in the bilge? They can look fine but be corroded.

[99fxst99]

Does the battery cable from engine to battery switch h lay in the bilge? They can look fine but be carroded.

Replaced a lot of Evinrude harnesses in 17 Whalers years back because they laid in a trough of water all the time.

[Dave Strong]

Bad ground some place.

Dave

[gfinch]

David Strong is my guess also. Look up Volt drop testing..... Poor grounds give the weirdest symptoms.

http://fme-cat.com/docs/1519.pdf

[Capt.Insane-o]

Main engine harness. Pull the fuses out of the holders and see what the sockets look like.

[flabum1017]

Thinking out of the box, what is your voltage at speed? Are you over-charging? High voltage can wreak just as much havoc as low voltage.