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Yamaha F250 Losing Power and Backfiring

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Yamaha F250 Losing Power and Backfiring

Old 04-15-2019, 09:04 PM
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If you're 100% sure you're getting a spark to all cylinders and you disconnected the coil wires with no change, it sounds like a fuel issue - did you ever try swapping the injectors around?
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Old 04-15-2019, 10:22 PM
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Originally Posted by Fwpratt View Post
that is the (optional) sensor for converting cooling water pressure to an electrical value,
for display by Command Link gauges / NMEA 2000.
The same sensor is alternatively used to convert pitot tube water pressure to speed.

That small metal hex is the original style,
which was notorious for allowing water to pass into the wiring harness,
causing havoc with the ECM reference voltage
and thus other essential operating sensor outputs.

The revised part has a much larger metal hex body.

Attachment 1098320
Thanks for that. I donít think this sensor has worked at all for me. I use GPS for speed on my gauge so I will probably do without for now. Water speed would be nice, but I can get by without it.

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Old 04-15-2019, 10:25 PM
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Originally Posted by REGMARINE26FS View Post
It sounded like a ground issue, or an electrical issue-----but i am not sure i could have found that one. Learn something new every day. Hopefully it will fix your problem
I sure hope so. I forgot to take pics of the wiring harness but will do so when I get back to the boat. If we didnít have to pull the powerhead to replace the oil pump and gasket, we never would have this. Since the extension harness was brand new, I never would have suspected that it would have failed after 4-5 months.

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Old 04-15-2019, 10:29 PM
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Originally Posted by DaveHNL View Post
If you're 100% sure you're getting a spark to all cylinders and you disconnected the coil wires with no change, it sounds like a fuel issue - did you ever try swapping the injectors around?
Not yet. We had to drain the oil to do the water test and then pulled the powerhead to do the water pump. Once we put it back together with fresh oil, we will see how it ru s. If it doesnít run, weíll swap injectors. Donít jinx me! Itís gonna run like a striped ape! LOL

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Old 04-16-2019, 01:44 AM
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Best of luck to you Captain Paul, after all you've been through, you deserve a break...
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Old 04-16-2019, 12:36 PM
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Originally Posted by DaveHNL View Post
Best of luck to you Captain Paul, after all you've been through, you deserve a break...
Thanks for your help!
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Old 05-04-2019, 04:46 PM
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Any updates to report?
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Old 05-04-2019, 11:08 PM
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I have an update but no good new. We replaced the oil pump and engine harness extension and put everything back together. Replaced the Racor filter, and added fresh oil. Fired it up and had the same problem. Wouldn’t run worth a shit. We changed plugs and it ran even worse. We were convinced that corrosion was causing an electrical issue. We didn’t see any codes in the engine monitor, however, there were three codes in the diagnosis records. Electronic Throttle system, Intake Pressure, and Intake Temp. We had used BraKleen to see if we had an intake leak so those codes made sense. We cleared the codes and ran it again and they didn’t come back. At this point we are stumped and at a loss. I don’t know what the hell to do at this point. I’ve run out of money to keep chasing this down.
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Old 05-05-2019, 03:35 AM
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You never replied as to whether you have checked the fuel pressure now it runs like shit all the time. What is fuel pressure now?
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Old 05-05-2019, 06:21 AM
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Have you tried the Yamaha Outboard Parts Forum? I've read some replies from a guy that goes by Rodbolt and he is very knowledgeable and helpful. Maybe you can get in contact with him.
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Old 05-05-2019, 08:10 PM
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Originally Posted by brendanm View Post
You never replied as to whether you have checked the fuel pressure now it runs like shit all the time. What is fuel pressure now?
I did reply. It was 44psi. That was the first shop that tested it last fall. The other two shops that tested it last month said it was fine. I didnít get the numbers. But has been running like shit since the end of September last year before all of the fuel pressure tests were done.
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Old 05-05-2019, 08:13 PM
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Originally Posted by tarpononecharter View Post
Have you tried the Yamaha Outboard Parts Forum? I've read some replies from a guy that goes by Rodbolt and he is very knowledgeable and helpful. Maybe you can get in contact with him.
I haven’t posted there. I can try that. I just wanted update everyone here since you all have tried so hard to help.


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Old 07-08-2019, 08:19 AM
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Any updates on this? Definitely sounds like a timing issue - did you happen to swap the oil control valves?
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