Engine Trouble - symptoms familiar?

[DividedSky]

I've been having an issue with my port side engine (2000 Yamaha 4 stroke, twin 225's).

We were running at about 4200 yesterday, and I noticed the port side engine kept cutting down to about 3500 on it's own, randomly and abruptly. Once it would return back to 4200, we would try to accelerate and it would actually lose power - dropping back down in the 3k range again. It really felt like the engine was choking on something.

We had a mechanic look at it, and he couldn't find anything. Both engines ran fine at 6k, passed any computer diagnoses, and we couldn't reproduce the problem, yet it was happening all day yesterday.

We've had this same issue 3 weeks ago and even tripped the engine alarm, not being able to get it back up above 1700, so we really feel something is wrong here, but once we shut down it takes hours of running to reproduce again.

Anyone have any thoughts?

 

[BobP]

Go to Yamaha authorized mechanic next time, computer will show those alarms.

 

[seasick]

I agree with BobP. The ECU will slow the motor when certain alarm conditions occur like low oil pressure or high water temp. There are other causes as well and without the Yamaha diag tools you won't be able to identify the culprit

 

[jehines3]

Check that plug wires are seated properly and none show any signs of leakage around the insulator. jh

 

[grady33]

Not an expert, but I had a similar problem 5-6 years ago. Have 2 stoke YAM EFI's and had this happen once and turned out to be the low pressure fuel pumps. Apparently there is a small membrane that can tear. Not sure 4 stokes have them but would assume so. I actually just replaced all 6 (3 per engine) just to be safe. Also, checked and replaced the VST filters which had never been done and were clogged up. Afterwards, all my RPM problems went away.

 

[JUST-IN-TIME]

what did the yami gauges say?

either
low oil
overheat

 

[DividedSky]

Well I should stress that we didn't have any kind of alarm yesterday when the port engine was acting up - just a dramatic alternating loss and recover of power, over and over, without the ability to accelerate at all beyond 4000 rpm.

The Yami guages didn't show a thing - no codes at all, which was disappointing. I ran it today for about 20 minutes and no issues. The issue with this is that it's hard to recreate the symptoms unless you run it for an hour or two, therefore they can't fix what they can't see.

 

[JUST-IN-TIME]

fueling issue then

 

[grady33]

Fuel or filter issue I would think.

 

[CJBROWN]

X3...sounds like water in the fuel.

 

[BobP]

Just n time, would the computer pick up what the motor did ?

 

[JUST-IN-TIME]

Just n time, would the computer pick up what the motor did ?

only if it threw a code or alarm

so if an alarm went off, yes like it did it will tell u the hr when it happened

 

[BobP]

And the computer will retain the codes until reset, or some time period?

I don't undertand the avoidance for getting professional evaluation considering how costly these motors are. If the guy had a 300 buck lawmower instead doing the same. may not think twice about dropping in the trunk and off to the dealer.

Even to just pay the dealer to query the computer and identify a fix, then do it youself, is so inclined.

 

[JUST-IN-TIME]

you can clear codes but u can not erase the history

 

[DividedSky]

Guys - we took this to a Yamaha certified mechanic at one of the largest and most reputable marinas in the state...I'm not sure where I mentioned that we took it to some random mechanic, but that's definitely not the case

 

[JUST-IN-TIME]

if he is good he would have had a fuel pressure gauge on the motor with a laptop while running the motor

 

[Twisted28]

Some mentioned it may be afuel issue but didn't he say it was only one motor, the port side. if it was fuel, it would be both, right?

 

[LI Grady]

Bad fuel pump maybe?

 

[seasick]

Swap the fuel lines just after the primer bulbs. If the symptoms move to the other engine, the problem is back of the bulbs, lines, filters, tank, pickups whatever.
if the problem stays with the same motor, look deeper into the engine.
By the way, check the oil level in the motor that is acting up. Insure that oil is not low OR too high (overfilled)

 

[JUST-IN-TIME]

just do the test i said
20x easier than swaping this and that!