Yamaha 90 sudden power loss then powers up again.

[ship happens]

Similar issue with a old 150 black max several years ago. After many attemps by marine mechanic to identify it was a stator issue, $$$ later. Hope yours isn’t heading in that direction.

Not with the 4 strokes. They draw power from the battery to drive the ignition through the ecu.

 

[Sea lyin’]

If it was fuel restriction it could possibly do that, however not likely. If it was a bad low or high pump it would die, not keep running. I would say its loosing a cylinder. Either an injector, plug or wire. I've seen all three what I just mentioned on the yammy stuff

If it was one of the above would it be intermittent? He’s had the motor a few years and has had it happen only twice.

 

[ab1752]

Does this issue just instantly cut off and cut on? I have suffered heat soak lots of times with old SU carbs, they don't hard start / stop, they stumble and sputter. If its a hard stop then run, that to me is spark.

 

[ship happens]

If it was one of the above would it be intermittent? He’s had the motor a few years and has had it happen only twice.

Yeah it's possible a fuel restriction could do that it's really highly unlikely but yeah its possibly. If the VST cannot draw fuel from the tank faster the outboard injection consumes then yeah it could stumble, sounding and feeling like a down cylinder or 2.

The anti syphon valve should be removed regardless.

 

[Sea lyin’]

Does this issue just instantly cut off and cut on? I have suffered heat soak lots of times with old SU carbs, they don't hard start / stop, they stumble and sputter. If its a hard stop then run, that to me is spark.

Running great in a dead straight line at WOT on glass calm lake. Motor just drops from right around 4800 to 1200-1500 rpm for less than about 20 seconds then powers back up to 4800 and carries on as normal. He says it’s never completely shut off and he’s never had to touch the throttle to correct the problem. It just does it on its own.

 

[Sea lyin’]

Yeah it's possible a fuel restriction could do that it's really highly unlikely but yeah its possibly. If the VST cannot draw fuel from the tank faster the outboard injection consumes then yeah it could stumble, sounding and feeling like a down cylinder or 2.

The anti syphon valve should be removed regardless.

Too small of fuel line? Not sure if that would show up at random times but maybe combined with a kink In the line or sharp bend somewhere?

 

[Sea lyin’]

Thanks for all the reply’s. There’s quite a few things for him to check now. More than we’ll be able to check in a single day. Keep the ideas coming and I’ll pass the info along.

 

[Sea lyin’]

If it was fuel restriction it could possibly do that, however not likely. If it was a bad low or high pump it would die, not keep running. I would say its loosing a cylinder. Either an injector, plug or wire. I've seen all three what I just mentioned on the yammy stuff

Also, would these show up on the scan when he’s able to get it done?

 

[sly_karma]

Sounds very similar to an issue I had with my merc. Full throttle, then drop down to just above idle out of no where. I would shut off, restart and all was good again until the next time. Mine ended up being the filter in the fuel bowl assembly. Could be this part. These should be changed every 500 hours.View attachment 61702

Ye gods!! I thought Etec parts were expensive! VST filter for mine is $3. (Although the official spark plugs are like 25 each and oil is north of $60 a gallon).

 

[ship happens]

Also, would these show up on the scan when he’s able to get it done?

No nothing will show up unless there is a hard fault like an injector shorted. Etc.

Like I said these guys are right it very well could be a restriction. Or it could be an injector or even a plug. Sounds stupid, but I've seen it alot on the 4 strokes.

Change fuel filters everywhere
Remove anti syphon valve

See what happens

 

[ship happens]

Ye gods!! I thought Etec parts were expensive! VST filter for mine is $3. (Although the official spark plugs are like 25 each and oil is north of $60 a gallon).

We sell a gallon of full synthetic for 45. Case of 4. 180 plus tax 4 gallons

 

[profisher]

If it just dropped a cylinder from an ignition missfire it would still run at more rpms than twice idle. It would probably not quite get up on plane and run rough. If it does have water cooling check that those cooling lines aren't plugged.

 

[ship happens]

Wont be going anywhere on 3 cylinders

 

[ab1752]

Start with the easiest stuff first, make sure all accessible + and - are clean and tight. Dump out the filters into a can so you can see how they look inside. Pull the plugs and see how they look. Go for a boot, ideally crack beers and celebrate NFF condition. Woot

 

[32Knots]

On my 250hp it was a cam sensor.

Would intermittently lose power like that and have to be turned off to go above 3000 again. Ran perfect otherwise. No alarms no codes. Puzzled boathouse and yamaha rep until they figured it out. 3 seatrials and laptops hooked up. even tried a different ecm etc

 

[Slabbedout]

Brothers boat, he’s got a 2014 90yamaha. Runs great except twice now at wide open throttle it has suddenly bogged down and slowed down to about double trolling speed but not quit. Then without touching anything it picked up speed again and continued on the rest of the journey with no problem. One trip was about 3 miles after it happened and the other was about 10 miles with no problem. And about 3 months use between the two incidents. It’s in storage now but he’ll be taking it to get scanned come spring. Til then anybody have any ideas?

Sounds to me like a fuel restriction / pump issue

I suspect 2014 is fuel injected ?

I bought a boat with a low hour 2001 40HP yammie that multiple shops said needed replacement because it would not run properly. Turned out to be the accelerator pumps sticking on 2 of the 3 carbs. It would do exactly as you say run great then just randomly bog down for a moment before running full speed again. It was super random and would only happen every couple trips but I never trusted the motor to go far.

 

[Sea lyin’]

Sounds to me like a fuel restriction / pump issue

I suspect 2014 is fuel injected ?

I bought a boat with a low hour 2001 40HP yammie that multiple shops said needed replacement because it would not run properly. Turned out to be the accelerator pumps sticking on 2 of the 3 carbs. It would do exactly as you say run great then just randomly bog down for a moment before running full speed again. It was super random and would only happen every couple trips but I never trusted the motor to go far.

Those are the symptoms but yes it is a fuel injected motor. After poking around a bit today, nothing stood out as obvious but the fuel line does pass through a bulkhead and to me seemed pretty tight in the hole. It’s pretty chilly here right now so when it warms up some he’ll start to dig into it in earnest.

 

[ship happens]

On my 250hp it was a cam sensor.

Would intermittently lose power like that and have to be turned off to go above 3000 again. Ran perfect otherwise. No alarms no codes. Puzzled boathouse and yamaha rep until they figured it out. 3 seatrials and laptops hooked up. even tried a different ecm etc

The 250s and all vblock injected 4 stroke engines use a completely different system for controlling the ecu. Not the same engine in any respect. They have 3 sensors that work in conjunction with a motorized throttle plate assembly.

The inline engines are mechanical with TPS like most fuel injected engines.

 

[lemmy]

I had the exact symptoms on my 02 225 4 stroke Yamaha . Changed both fuel filters and havent had a hiccup since.

 

[searun]

No nothing will show up unless there is a hard fault like an injector shorted. Etc.

Like I said these guys are right it very well could be a restriction. Or it could be an injector or even a plug. Sounds stupid, but I've seen it alot on the 4 strokes.

Change fuel filters everywhere
Remove anti syphon valve

See what happens

Sound advice. Would also check and replace the squeeze bulb, and also make sure your fuel tank vent is functioning properly. The problem corrects itself after the built up pressure from some blockage is relieved, which points to either a blockage or venting issue. With today's modern fuel management/control systems its likely any major faults would show a fault code. If there is no fault code, then problem is more likely within the fuel system itself.