Loss of power / won't reach WOT

lakeliving

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Do those I/o motors have a port to plug in a diagnostic meter like a car?
 

jhill

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Will it rev up high rpm in neutral if you momentarily rev it like a hotrodder?
 

Tin Diesel

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Those are two great questions : I don't know if it has a diagnostic port.
Regarding the rev in neutral, it puts out an alarm if I rev past a certain rpm... I think about 1500. I assumed this is a standard warning alarm, but now I'm wondering if it is telling me something else?
 

Tin Diesel

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So, I give up - taking her in to Bowden Marine (certified Mercury repair shop north of Houston) on Thursday. There is, apparently, a diagnostic port because he said "we'll get her hooked up and see what's goin' on...".

I'll let y'all know.

Break Out Another Thousand...
 
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lakeliving

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Hopefully it's something minor and you're back on the water soon.
 

BigKahuna

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Yes there is a diagnostic port on top of Mercruiser I/O's. On my 4.3L it was near the distributor/cap. Your Mercruiser engine guardian system is performing exactly how it's supposed to. It's limiting the RPMs preventing damage to your engine. With the diagnostic scan tool it shouldn't take them long to figure out what's up. You'll be back on the water in no time. Be positive. There's plenty of summer left!
 

jhill

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Yes there is a diagnostic port on top of Mercruiser I/O's. On my 4.3L it was near the distributor/cap. Your Mercruiser engine guardian system is performing exactly how it's supposed to. It's limiting the RPMs preventing damage to your engine. With the diagnostic scan tool it shouldn't take them long to figure out what's up. You'll be back on the water in no time. Be positive. There's plenty of summer left!
.....so it is in limp mode (reduced power) because of a fault code.....makes sense so you aren't stranded on water. Funny they don't add "check engine" light on dash so you are aware it needs error diagnosed
 

BigKahuna

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Yup it's designed to get you back to where you need to go so you are not stranded.......
 

Tin Diesel

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Guardian system makes sense - it is so consistent. I searched for what the Guardian monitors and came up with the following brochure. My guages tell me temp, oil pressure and voltage are OK. Perhaps it's seawater pressure...
20200707_065801.jpg
 

Tin Diesel

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Update: the Mercury dealer finally hooked it up and said it was throwing numerous engine fault codes. His initial diagnosis was fouled plugs. He said that my engine has a tendency to that. $425 (plugs $180, the rest labor and tax)

Haven't had it out on Lake yet, but I ran it in my driveway and as the dealer said, the engine was much smoother. MUCH smoother!

In the driveway it used to sound like a dragster at idle... loud brap brap brap. On the water, I always thought it was loud. I now realize this was a lot of misfires. This is my first motor boat and I bought it used, so I don't have a basis of comparison.

Now, she just hummms!

If Hurricane Hanna is gone in time, I may try to get her out tomorrow for a test run.

Also, I bought the Vesselview Mobile and installed it. Seems pretty cool. Looking forward to trying that out also.
 

Jack M

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I was fouling plugs after I moved . The other marina I was at is on a lake ,the marina I am at now is in a cove on a river and a 35-40 minute ride in a no wake zone to a lake . After changing out fouled plugs 2 years in a row the mechanic at the dealer asked what I was doing different to foul the plugs . I explained the move and was told after I get out of the river to open it up for 5 minutes or so . No fouled plugs since
 

BigKahuna

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Update: the Mercury dealer finally hooked it up and said it was throwing numerous engine fault codes. His initial diagnosis was fouled plugs. He said that my engine has a tendency to that. $425 (plugs $180, the rest labor and tax)

Haven't had it out on Lake yet, but I ran it in my driveway and as the dealer said, the engine was much smoother. MUCH smoother!

In the driveway it used to sound like a dragster at idle... loud brap brap brap. On the water, I always thought it was loud. I now realize this was a lot of misfires. This is my first motor boat and I bought it used, so I don't have a basis of comparison.

Now, she just hummms!

If Hurricane Hanna is gone in time, I may try to get her out tomorrow for a test run.

Also, I bought the Vesselview Mobile and installed it. Seems pretty cool. Looking forward to trying that out also.
Oh yeah those plugs arent cheap. I'm assuming they're iridium??? But they perform well and last long. Hope this solves your problem......
 

SEMPERFI8387

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Oh yeah those plugs arent cheap. I'm assuming they're iridium??? But they perform well and last long. Hope this solves your problem......
Nothings cheap when it has “Marine” in front of it (except maybe me:p) When I had my old jet boat and was constantIy changing plugs, I cross referenced my “marine plugs” to regular and price was like 75% less ..:oops:
 

BigKahuna

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Nothings cheap when it has “Marine” in front of it (except maybe me:p) When I had my old jet boat and was constantIy changing plugs, I cross referenced my “marine plugs” to regular and price was like 75% less ..:oops:
Yup used to do the same in our first boat. Back then the AC Delco "marine" plugs were $6 or $7 a piece. Regular automotive ones were a dollar. Put them together and they were identical! Same with the oil filters......
 

Tin Diesel

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Got the boat out on the lake today... WOW!
Feels like a new boat!
Engine is smooth and much quieter.
Accelerates aggressively.

I hit 5000 rpm easily - more left on the throttle. I think I got to 38 mph on gps. My wife was getting nervous so I didn't take time to tweak the trim before I backed off.

According to the Mercury prop selector my calculated max speed with this prop is 42.7 mph so I'm pretty satisfied.
:cool:
 

lakeliving

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Great news!
 

Tin Diesel

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Thanks. As I said, this is my first motorboat and we bought it used, so we have no baseline for comparison.

We were thinking today that it has never run this well. The plugs were possibly bad from sitting unused for 3+ years before we bought it, and kept getting worse in the 3 years since.

Today, during 2 hours of run time, it seemed to get smoother. As Jack M said... maybe some high speed blow out helped?
 

BigKahuna

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Thanks. As I said, this is my first motorboat and we bought it used, so we have no baseline for comparison.

We were thinking today that it has never run this well. The plugs were possibly bad from sitting unused for 3+ years before we bought it, and kept getting worse in the 3 years since.

Today, during 2 hours of run time, it seemed to get smoother. As Jack M said... maybe some high speed blow out helped?
Wow at least 6 years without changing the plugs. I bet you won't do that again. While you are at it have them check the distributor cap and spark plugs wires. Especially if they are the originals. Also put a can of Seafoam in your gas tank. Clean those fuel injectors.......Have you changed the impeller?
 

Tin Diesel

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Yes, impeller changed 2 years ago (less than 70 hours)
 

Tin Diesel

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Thanks for the advice on the other stuff
 
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