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2004 Yamaha 300 HPDI Poor Idle

Old 03-04-2019, 05:29 PM
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I've replaced the 4 mystery filters in the HP pump and the 6 injector filters.
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Old 03-04-2019, 06:56 PM
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I still think it will ultimately end up being an air leak in the fuel line or bad low pressure pumps. I know you've checked but they are common sources of your exact problem and if the tpms voltage is set correctly there isn't much else I can think of since you have a good WOT.
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Old 03-05-2019, 02:57 AM
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I ordered a new fuel bowl. That's the only thing I haven't replaced. O-ring was already replaced. I'm thinking the samething. Thanks.
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Old 03-13-2019, 06:31 PM
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Fuel bowl and VST filter replaced. Hopefully test run next week when the weather gets better.
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Old 03-13-2019, 07:06 PM
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Do you have YDS? If so, what's the throttle plate opening at idle?
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Old 03-14-2019, 02:36 AM
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YDS reads .60v and 2 - 2.1 degrees angle. I've tried .58v - .62v on the TPS and didn't make a difference. Link and sync has been done 4 times and no change. I also double checked the LPFP and they are good.
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Old 03-15-2019, 11:39 AM
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Took the boat for a test run and it still idles horrible. After the fuel bowl was replaced. It will not stay full. Replaced the o-ring and still won't stay full. I'm about to remove the fuel bowl assy., LP fuel pumps and install a low pressure electric fuel pump inline before the fuel filter in the boat. Tried to readjust the TPS per the service manual and YDS. Seems to run rough until it gets above 1600 rpm - 1800 rpm and then seems to smooth out some. I tried to do a injector test and when the engine is shut down. the high pressure pump leaks down to around 400 psi. Is this normal? The high pressure pump is running 980-990 psi at idle. Maybe injectors leaking??? I thinking about pulling them and have them cleaned and flow checked.
Any thoughts????
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Old 03-15-2019, 12:09 PM
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Thermostat stuck open????
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Old 03-15-2019, 12:26 PM
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Check the pressure regulator and filter on top of the VST
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Old 03-15-2019, 01:01 PM
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Thermostats were replace 2 weeks ago. I checked the pressure regulator and screen and planning to recheck it. The medium pressure fuel filter was replaced.
Checked the fuel pressure regulator and the fuel pressure would drop to 43 psi with 15-20 in vac on the regulator. As the vacuum dropped on the gauge. The pressure came back up.

Question: I put a vacuum on the regulator before starting to see if it would hold vacuum and it would drop slowly. Is that normal? or should it hold the vac?
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Old 03-15-2019, 03:54 PM
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I didn't pull the regulator to check the filter this time. Which side of the filter gets dirty? The side closest to the regulator or the backside of the filter?
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Old 03-15-2019, 04:01 PM
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Throw new plugs in it, one year old plugs are old. Remove, clean, check, and retighten every ground wire you can find.
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Old 03-15-2019, 04:28 PM
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The plugs are new. They have about 2 hours on them. I'll recheck the the grounds. Thanks for the info.
Correct me if I'm wrong.... Would leaking or dirty injector/injectors cause my issue at low speed?
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Old 03-15-2019, 05:47 PM
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Check all the grounds and all were clean and tight.I did clean all of them while I had them apart. Couldn't find any issues with the grounds.
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Old 03-17-2019, 07:51 AM
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You mentioned you changed the filters on your injectors. Did you send out the injectors to be serviced (ultrasonic cleaning)? "Changing the filters is not enough to get the injectors performing properly. The services check them before and after. Poor injector performance is often cause of poor idling.
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Old 03-17-2019, 04:28 PM
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Thanks for the reply Capt Harv. Injectors any out to Injector Clinic in Hobe Sound, Florida for cleaning. Hope to have them back next week.
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Old 03-27-2019, 08:27 AM
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Well, the injectors were flow checked and flow and pattern are good on all injectors. No problem found. I should have them back this weekendand reinstall them. Any more suggestions?
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Old 03-27-2019, 08:31 AM
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High pressure pump/s service, all 10 micro filters, metal canister filter, pressure regulator/screen, vst pump filter, low pressure pumps, paper filter/o-ring, water separator or any other pre-motor fuel system leaks.
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Old 03-27-2019, 08:39 AM
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Thanks for the info Luke. All has been done except for the fuel pressure regulator screen. I did pull the regulator and the screen looked clean. I plan to pull it again and pull the screen and check it. The regulator is working correctly. It was tested per the service manual. All filters have been replaced and all 4 screens in the pump and 6 injector screens have been replaced.
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Old 03-27-2019, 04:05 PM
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Cleaned the regulator filter today. Waiting on the injectors.
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