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Old 06 April 2019, 08:38   #1
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Please help with Yamaha 150hp 4 stroke issues.

Hi folks, Iíve was pointed in the direction of this forum in hope of fixing a long term engine problem Iíve been having. Itís stumped myself and 2 mechanics for the last 2 years and Iím finding myself at a bit of a loss. The following is as detailed an outline of the problem well as some theories and solutions we have already tried. All input welcome!.

Engine:
Yamaha 150 4 stroke which bought new with this zeppelin rib in 2009.*

No previous issues, serviced and winterized yearly.*

Fuel system:
The boat has an Internal fuel tank. The fuel line runs short distance up from tank connection to fuel filter in the console. From fuel filter the fuel line continues the length of the boat back to engine and into its internal smaller fuel filter as normal. There is also a hand primer bulb in console. All a very standard setup.*

So... now to describe the problem:
The engine starts perfectly and gets up to full speed on flat water with no problems. *On flat to small choppy conditions everything *is 100% perfect.*

The problem arises as the swell starts to build (only slightly) and the banging this causes begins to increase. I will be cutting through a very small sea state nicely and as it builds just a small bit she will come down from a wave with a slightly bigger bump and instantly the engine will change from itís nice perfect revs to a chug with a bit of a wobble that can be felt in the wheel. I can keep the throttle at the same position but the engine sound has completely changed to what I would *describe as a rumble with an associated vibration. If I increase throttle speed the rumble and vibration or imbalance increase and she is under powered. If I bring the throttle back to neutral the rumbling/vibration decreases with revs but *if I again increase power they increase also.

There is no clear method to fixing this issue on the water but the following have worked. 1) turn her off for a few seconds and restart. This doesnít always work as the problem can still be there upon restart. 2) after trying a restart drive at lower revs and bring up the speed. This some times works some times doesnít.*

When doing number 2 above and driving at say 40% on the throttle (noting she is vibrating and under powered) she can suddenly kick in to being perfect again for a few seconds, then back to a wobble, then back to perfect on and off until the issue clears and sheís back to running smooth.. until the next wave of the right size.*

One thing to note, when I say swell above I mean very small swell or even large wind chop. Just enough to get a bang vibration through the hull. *

An engine fault does show by means of a slow flashing engine symbol which seems to flash every 5 seconds.*

We ran engine diagnostics live while engaging the problem and it showed no faults but did indicate that the engine could be entering ďguardian modeĒ

Another thing Iíve noticed. When this issue kicks in and I return the throttle to neutral and there is still a wobble in the engine *the idle revs seems smooth when I rise them.*

What we have tried so far:*
Theory 1) injectors:
The first mechanic removed injectors and cleaned and reinstalled them but the fix didnít seem to do much if anything. All in all we have tried this 4 times over the years and while it might seem like it had some effect at first the problem soon returns.*

Theory 2) bad spark plugs, loose filters, fuel line issues:
All of these have been changed and checked multiple times except the fuel line we havenít run a new one. No dirt or water has shown up in any of the filters. The fuel tank does have a second outlet for a second engine, I changed the fuel lines to this and the problem was the exact same.*

Theory 3) Apricots or loose debris in the fuel tank. I had trouble with this theory for 2 reasons. Firstly, if I bring the boat up to say 75% speed and then kink the fuel line by the tank, there is no effect on the engine for some time as it stall has all the fuel in the lines as well as the fuel filters etc. If something is suddenly stirring in the tank I canít see how it would have an instant effect on the engine as this problem kicks in instantly. My second issue is that no debris of any kind has ever shown up in the filters. I will try and test an external tank this week just to be sure.*

Theory 4) electrics.*
I was told that a bad connection in my isolater switch could be causing the issue which engages *from the bang of a swell. I bypassed the switch and the problem continued as normal.*

Other theories)
Air entering fuel line.
Wiring loom problem.

There have been periods where this issue was worse. During this times it would be there from the moment you start the engine and with an even more notable imbalance and associated chugging sound. Other times itís more resilient and takes a bigger bang to engage the issue.*

There really isnít much rhyme or Rhythm to it. Just the fact that a small bang to the boat which she has always handled no problem now causes this issue.*

Any help, theories or thoughts with this would be greatly appreciated. Itís been plaguing my now for 2 years and I donít know what else to do. The boat is seems so close to being perfect, I just need to solve this issue.*

Please add any follow up questions below.*

Thanks for reading,
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Old 06 April 2019, 12:17   #2
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Quote:
Originally Posted by Alex88 View Post
Hi folks, Iíve was pointed in the direction of this forum in hope of fixing a long term engine problem Iíve been having. Itís stumped myself and 2 mechanics for the last 2 years and Iím finding myself at a bit of a loss. The following is as detailed an outline of the problem well as some theories and solutions we have already tried. All input welcome!.



Engine:

Yamaha 150 4 stroke which bought new with this zeppelin rib in 2009.*



No previous issues, serviced and winterized yearly.*



Fuel system:

The boat has an Internal fuel tank. The fuel line runs short distance up from tank connection to fuel filter in the console. From fuel filter the fuel line continues the length of the boat back to engine and into its internal smaller fuel filter as normal. There is also a hand primer bulb in console. All a very standard setup.*



So... now to describe the problem:

The engine starts perfectly and gets up to full speed on flat water with no problems. *On flat to small choppy conditions everything *is 100% perfect.*



The problem arises as the swell starts to build (only slightly) and the banging this causes begins to increase. I will be cutting through a very small sea state nicely and as it builds just a small bit she will come down from a wave with a slightly bigger bump and instantly the engine will change from itís nice perfect revs to a chug with a bit of a wobble that can be felt in the wheel. I can keep the throttle at the same position but the engine sound has completely changed to what I would *describe as a rumble with an associated vibration. If I increase throttle speed the rumble and vibration or imbalance increase and she is under powered. If I bring the throttle back to neutral the rumbling/vibration decreases with revs but *if I again increase power they increase also.



There is no clear method to fixing this issue on the water but the following have worked. 1) turn her off for a few seconds and restart. This doesnít always work as the problem can still be there upon restart. 2) after trying a restart drive at lower revs and bring up the speed. This some times works some times doesnít.*



When doing number 2 above and driving at say 40% on the throttle (noting she is vibrating and under powered) she can suddenly kick in to being perfect again for a few seconds, then back to a wobble, then back to perfect on and off until the issue clears and sheís back to running smooth.. until the next wave of the right size.*



One thing to note, when I say swell above I mean very small swell or even large wind chop. Just enough to get a bang vibration through the hull. *



An engine fault does show by means of a slow flashing engine symbol which seems to flash every 5 seconds.*



We ran engine diagnostics live while engaging the problem and it showed no faults but did indicate that the engine could be entering ďguardian modeĒ



Another thing Iíve noticed. When this issue kicks in and I return the throttle to neutral and there is still a wobble in the engine *the idle revs seems smooth when I rise them.*



What we have tried so far:*

Theory 1) injectors:

The first mechanic removed injectors and cleaned and reinstalled them but the fix didnít seem to do much if anything. All in all we have tried this 4 times over the years and while it might seem like it had some effect at first the problem soon returns.*



Theory 2) bad spark plugs, loose filters, fuel line issues:

All of these have been changed and checked multiple times except the fuel line we havenít run a new one. No dirt or water has shown up in any of the filters. The fuel tank does have a second outlet for a second engine, I changed the fuel lines to this and the problem was the exact same.*



Theory 3) Apricots or loose debris in the fuel tank. I had trouble with this theory for 2 reasons. Firstly, if I bring the boat up to say 75% speed and then kink the fuel line by the tank, there is no effect on the engine for some time as it stall has all the fuel in the lines as well as the fuel filters etc. If something is suddenly stirring in the tank I canít see how it would have an instant effect on the engine as this problem kicks in instantly. My second issue is that no debris of any kind has ever shown up in the filters. I will try and test an external tank this week just to be sure.*



Theory 4) electrics.*

I was told that a bad connection in my isolater switch could be causing the issue which engages *from the bang of a swell. I bypassed the switch and the problem continued as normal.*



Other theories)

Air entering fuel line.

Wiring loom problem.



There have been periods where this issue was worse. During this times it would be there from the moment you start the engine and with an even more notable imbalance and associated chugging sound. Other times itís more resilient and takes a bigger bang to engage the issue.*



There really isnít much rhyme or Rhythm to it. Just the fact that a small bang to the boat which she has always handled no problem now causes this issue.*



Any help, theories or thoughts with this would be greatly appreciated. Itís been plaguing my now for 2 years and I donít know what else to do. The boat is seems so close to being perfect, I just need to solve this issue.*



Please add any follow up questions below.*



Thanks for reading,


If when the problem happens, have you tried putting the engine into neutral & increasing the revs. Does the wobble continue or does it disappear when in neutral?
Have you checked the ingear start protection switch in the throttle?
I donít know about Yammies, but Etecs have a switch to drop the revs when going into gear.
Short/open cct in wiring loom?
It sounds like it could be losing a cylinder, have you checked the coils/ht leads.

All the above is a bit of a scattergun approach, but you never know.
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Old 06 April 2019, 14:40   #3
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I agree you are losing a cylinder. If it comes back as you describe Iíd say itís electrical. HT leads would be my start point if the plugs are new. A bad connection there will let it arc
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Old 06 April 2019, 16:38   #4
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HT leads do sound plausible. Take leads off. Clean and emery brush contacts, and torque down. Have you tried a continuity test on the electrics? Most wiring looms aren't tinned. Not sure that would cause the issues you have, but worth checking. The cable degrades and you lose connection. Can you purchase some second hand HT leads to test?
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Old 06 April 2019, 19:39   #5
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I had something similar on a 2005 Yam 150 4-stroke. Yamaha dealer mechanic advised I change the injector pump. Didnít solve it. In the end replaced the injectors and it was fine after. Have a look on eBay in the US (eBay.com) - there are much much cheaper injector options there than from Yamaha.
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Old 07 April 2019, 02:13   #6
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I think Pikey Dave may be on to something. My mates yam f150 has several relays/solenoids under the engine cowling. One of these is designed to limit the engine revs when the boat is out of gear. I presume it knows this because it knows its in neutral.Might one of these be failing? ill see him this week and get more info from him. It does sound very electrical as it happens so suddenly after hitting a wave. As Dave asks , if you close the throttle immediately the problem starts and put it in neutral, then raise the revs by using the idle lever does it rev cleaner then?? I would have thought that if you go out first thing a.m. on flat water and give it the beans/flat out for say 4 mins, that would put the highest demand on the fuel system from injectors to lines to filters, the lot.If it doesn't miss a beat then , I'd have thought its electrical. Keep us posted...its how we learn! Nik
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Old 07 April 2019, 10:09   #7
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I did have a similar problem with a Yam waverunner, but not as harsh, and sometimes it would completely die. Fine in calm water, hit some swell, and bang, issue!Don't think it the cure but it's worth a try-Turned out to be a dodgy earth connection on the battery. May be worth going through the earth points. As I said, probably unlikely , but worth a shot.
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Old 07 April 2019, 14:46   #8
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Thank you all!.

Ill check the earth connections and clean the HT leads.

Injectors have been cleaned many times but maybe a replacement is needed.. I did hear there were some bad injectors out there.

She will go flat out perfectly on the flat so ya.. I guess that can rule out fuel lines etc.

My gut is now almost certain its electric.

I will keep you updated on progress as I go. If any other ideas come to mind feel free to keep them coming.

Appreciate the help.
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Old 07 April 2019, 15:02   #9
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Check the caps on the HT leads where they are connected to the lead, vibration can create a gap and you will them lose spark at the plug
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Old 07 April 2019, 15:11   #10
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If your loosing a cylinder is the over rev limiter faulty

Fuel pick up in the tank clear of debris and not flexing so when you drive hard it picks up air being sloshed around.
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