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2008 yamaha f150 4 stroke power loss

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Firemedic0822

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So I have a 2008 yamaha f150 4 stroke with 490hrs and about4 weeks ago while on vacation with the boat I wasn’t able to get max rpm. Prior to going on vacation I changed themotor and lower oil, changed the plugs and all of the fuel filters. Trimmed I can usually get 6000 rpm out of themotor. I have owned the boat since newand have always used pump gas…..i know I know. But I have never had a problem with the boat….ever.
Originally I thought it was water in the fuel so while onvacation I had the tank cleaned and the fuel polished. An additive, gas shok was added by the fueltank cleaning company and that did increase performance. The day the tank was cleaned I ran the boataround 2000 rpm for about 2 hours and I was able to get about 4800 rpm out ofthe motor at about 85% throttle. I wasable to get higher rpm intermittently by pumping the throttle but it would dieback down to around 3000rpm at WOT. The following day I fueled up at the dock withrec 90. After that the problem came backand was only able to get 3000 rpm out of the motor.
Since the problem started I have purchased the Yamaha YDSprogram to see if it was throwing any codes. It had a few codes but from back in 60 and 100hr range.
Compression test showed
199psi cyl 1
203psi cyl 2
190psi cyl 3
195psi cyl 4
Fuel pressure was 48psi at the fuel rail
Shop tank was run and same symptoms
Fuel tank was completely changed along with fuel lines,racor and motor filter (tank had holes from pitting on the top of the tank soit had to be replaced).
Drained the VST
Injectors were tested at 2500 rpm on a hose and disconnectedand I got an rpm drop on all cylinders
Ignition was checked on a hose with an ignition tester andby pulling the wires off of the plugs and got drops in RPM with this test


Checked the mech fuel pump diaphragm for any tears andchecked the plunger for wear

With the YDS software, the TPS was showing very erraticvoltage so we assumed it was that. TPSwas ordered and replaced.


Fast forward to yesterday….
I took the boat out and ran it after setting the TPS voltageand got the same result. 2000rpm. The boat idles very rough and pops all overthe place. Going from idle andthrottling up the motor will stall. Idid notice that the IAC gets very very hot. You can hear the rattle when you shut the motor off but when I pulled itoff to see if it would open and close it doesn’t do anything.
So needless to say I am pretty stumped and any help would begreat!!
TIA
 
Can you post a YDS report of the engine at idle after it's warmed up?

Also remove the spark plugs and take some pictures.

Also, confirm that all the plug wires are actually producing good spark with a spark tester.

Finally, did you measure the fuel pressure within 3 seconds after key-on? If you only took the measurement when it was running, I would check what it is at key-on. It should be about 45psi at key-on, and 38 while idling after warmup.
 
rejesterd said:
Can you post a YDS report of the engine at idle after it's warmed up?

Also remove the spark plugs and take some pictures.

Also, confirm that all the plug wires are actually producing good spark with a spark tester.

Finally, did you measure the fuel pressure within 3 seconds after key-on? If you only took the measurement when it was running, I would check what it is at key-on. It should be about 45psi at key-on, and 38 while idling after warmup.
Click to expand...

I will take a pic of the plugs and get the yds info. I will also run another fuel pressure check. But I’m pretty sure it was around 40psi without the motor running. You can hear the fuel pump turn on and the pressure goes up key on motor off.
 
If it's 40 at key-on, that's a bit low. And if it was 48 while idling, that's definitely too high. The pressure regulator might be stuck.
 
Docksidemarineservices said:
You cleaned the fuel tank and have new filters and fuel.....You should have had the injectors cleaned also. Have them done.

Did you adjust any screws on the throttle plates besides the base idle screw?

Your TPS voltage should be around .7 volts
Click to expand...

The tank was completely replaced along with all fuel lines and filters. TPS voltage at idle is .7. I have not adjusted any throttle screws. I am going to order some rebuilt injectors tomorrow. I found them for about $60 for Bosch replacements.
 
Firemedic0822 said:
The tank was completely replaced along with all fuel lines and filters. TPS voltage at idle is .7. I have not adjusted any throttle screws. I am going to order some rebuilt injectors tomorrow. I found them for about $60 for Bosch replacements.
Click to expand...

DO NOT ORDER REBUILT INJECTORS! There really is no such thing.


Pulls your out, find a local shop and have them cleaned and serviced. Around $25 each for the service W/filters and o-rings. Simple job on your 150.
 
Docksidemarineservices said:
DO NOT ORDER REBUILT INJECTORS! There really is no such thing.


Pulls your out, find a local shop and have them cleaned and serviced. Around $25 each for the service W/filters and o-rings. Simple job on your 150.
Click to expand...

There are a few places that sell cleaned serviced injectors. I was going to order them and send mine out for service so I have an extra set. I found these guys

https://www.newenglandinjectors.com...low_Tested_Cleaned_(4)_63P-13761-00-00.html#/

any thoughts on that plan?
 
rejesterd said:
Can you post a YDS report of the engine at idle after it's warmed up?

Also remove the spark plugs and take some pictures.

Also, confirm that all the plug wires are actually producing good spark with a spark tester.




Finally, did you measure the fuel pressure within 3 seconds after key-on? If you only took the measurement when it was running, I would check what it is at key-on. It should be about 45psi at key-on, and 38 while idling after warmup.
Click to expand...

Here is the yds info
...also when turning on the key the fuel pressure initially jumped to 50psi after about 10 seconds it dropped to 39psi and stayed there

While running at idle fuel pressure was 43 psi. I didn't have time to pull the plugs but I did use a spark checker and it was showing it had spark.

I also pulled the plug wires off when it was running and each cylinder dropped rpm and would immediately regain rpm before the plug wire was fully attached to the spark plug.
 

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Yeah, the fuel pressure seems high, even at key-on. Clogged injectors wouldn't do that. They could certainly be clogged, so it's a good idea to have them cleaned, but I would take a closer look at the pressure regulator. Seems like it's stuck.

However, your YDS shows idle speed is only 585 rpm. That's definitely too low. So I would go through the link/sync procedure outlined in the service manual. That could be contributing to the problem as well.
 
rejesterd said:
Yeah, the fuel pressure seems high, even at key-on. Clogged injectors wouldn't do that. They could certainly be clogged, so it's a good idea to have them cleaned, but I would take a closer look at the pressure regulator. Seems like it's stuck.

However, your YDS shows idle speed is only 585 rpm. That's definitely too low. So I would go through the link/sync procedure outlined in the service manual. That could be contributing to the problem as well.
Click to expand...


Ok awesome. I’ll take a look at the service manual and pressure reg. I will have the injectors tomorrow so we will see.
 
Docksidemarineservices said:
Good deal.
Click to expand...
Chris - Just for my own curiosity.. Do you know if clogged injectors would cause the fuel pressure to increase at key-on? Seems like it should not matter in that case. Looking back on the OP's numbers, it seems like his gauge is just a little off (because key-on and idle pressure are exactly 5 psi off the spec).

Also to the OP - If you have time, I'd be interested in seeing a new YDS report while idling. Just to see what (if anything) changed. I'm surprised the idle speed was as low as it was. Just wondering if new/cleaned injectors would bring it back up to 650-700.
 
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