Mariner 175 Magnum EFI performance problem

[ronb]

I am going to post this in the Merc forum as well but, I'm hoping someone here has some advice too.

My 1992 184 SCR with a 1992 mariner 175 Magnum EFI, with 6 inch jackplate, and 24 pitch Tempest Plus prop has been getting 65 gps at 6000 to 6200 rpms all summer long. 65 with just me in boat, 59-60 with co angler aboard.

This last weekend at a tournament at paint Creek lake ( which I won BTW ) I prefished alone on Saturday and had a co angler on Sunday.

My problem is I couldn't get the boat over 51 mph at 4500 rpms. Sometimes I couldn't get over 47 mph at same rpms. I didn't notice the motor sounding rough.
When I got home, I pulled the plugs one at a time and found 5 plugs had some carbon on the disc...the top right plug was clean as a whistle and looked brand new. All of the plugs had some oil on them but the top rght had barley any sign of oil. The only thing I have done to the motor since spring was have the oiler removed and I mix my own oil 50/1 and put in Stabil and I have used Quick Clean the last two tanks.

Could my coil be bad and I am not getting fire to that one plug? Or does anyone know of something else that could be bad? Plugs are cheap and I plan on replacing all this week.

Thanks,
Ron

[Charlie206]

A clean, used plug generally means water is entering the combustion chamber. Do not run it anymore. If you are mechanically inclined do a compression check then pull the head and see if the head gasket failed. If it did not, look for a crack in the block.

[ronb]

I just got off the phone with a tech who just told me the same thing.

[Eyra1]

I actually had something similar happen to my 96 Mariner 175 Magnum EFI in 2008, loss of power like that.
Shut it down and got it to a dealership. Recommend/replaced both head gaskets as the left one was basically disintegrated and the right one was going bad.
Tech also took time to show me the pistons/cylinders while we had it on the operating table so to speak....said I was very lucky, no cracks/scuffing or pitting along the walls.
Good luck

[rchavis]

You could also have a switch box going bad also , mind 2.5 / 200 did that last year ,but think all the plugs had oil on them but sound like the same problem could not not get the rpms know more than 4600 rpms the battery cable came lose or the tech dont tighten them down when he rebuild the motor dont know because of the break time ?

[Eyra1]

I replaced my switch box this summer . Boat ran fine out to the fishing then engine would not start, like I had activated the kill switch.
So far since owning the motor I've replaced the power trim motor, voltage regulators, wiring harness, head gaskets, switch box and lower unit seals.
Damn thing is practically new now.................bought it in 2007. Now it is paid for!

[ronb]

I am scheduled to have it checked out tomorrow morning. The tech said the first thing is going to be a compression check and then spark test. When I bought the boat last january, I was getting 110 to 115 all the way around..I'm sure hoping it is the same.

I'll post the results.

Thanks folks,
Ron

[ronb]

I had the boat checked today at a local boat shop. compression test showed 115 on all cylinders except one, which was 110. Tech said spark seemed weak on top right plug, so boat got all new plugs, and replaced one coil and oe spark plug wire. Tech also showed me where one of my thermostat housings was leaking and allowing water to run down over my plugs (left side) so he checked thermostat and resealed the housing.
tech also topped off my trim oil.

All together he worked on my boat for 2.5 hours...total bill was $73.00 (he gave me a coil and got me plugs at his cost.)
It's a small shop that does not have a computer to hook to motor or anything like that so I won't know for sure if that completely fixed the problem until I can get it out and run it but, having good compression made me a lot happier.

[ronb]

Disreguard my last post....
Took the boat out to Brookville lake today to try it out.
Right from the start something was wrong..didn't sound right at idle.
I couldn't get any rpms at all...After a few minuted of removing the cowling and checking the plugs...the boat started to run great. I was at 60 mph gps and had pedal to go....then the motor lost all rpms and was back to idleing only.
When I was running, I had 15 psi water pressure at 5000 rpms.
Not sure what else it could be.
I going to a real shop tomorrow.

[hopalong1954]

power pack just went out on you.

[ronb]

How much is a power pack?

[Eyra1]

With install.....good bet would be $300 range........shop is so busy here, took boat sitting at the dealership 3 1/2 weeks for a 3 hour job. Went by the shop the late afternoon the day before it was serviced "Sorry, we've just been running behind. Everytime we get ready to get your boat in it seems something else came up. Should be first thing tomorrow." Next day, part apparently there, they open at 8am and at 11am were calling me to say it's ready.
But it runs like a scalded cat...........

[Lea]

OK, this might sound dumb, but been there....Is it possible that a bit of debris is getting into the carb jet? I had it happen. One minute great perforamnce, the next, back to almost idle...

[ronb]

Lea,
My motor is fuel injected, so I'm praying it's not something computerized that controls the fuel feed...something stuck sounds much better than something fried. I have had good fortune this year, boat has been great, caught lots of fish, won my first tounement....now just hoping the luck holds out and it's something simple!! The shop said he would squeeze it in and get it back to me before my next tournament on the 7th and 8th of August.

Thanks Everyone

[Lea]

I should have noticed the EFI in your post title...

I have no idea if anything can get stuck in that type of fuel feed, but sure hope it is simple. Keep us posted.