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Old 25-01-2025, 22:26   #1
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Hard Start after HP pump o-ring replacement

Story and back story. About a year ago I replaced my tank vent and lift pump on my Yanmar 3GM30F in sailboat. Afterwards I chased an air leak that made me have bleed system every time I started the motor. I have a factory installed electric pump that I can turn on to assist with bleeding. It was inconvenient but easy to do. I just turned on the pump and bleed at banjo bolt inlet to HP injection pump. Motor would the start right up and run fine for hours. After 8 hours shutdown I would need to bleed again. Always had some diesel on the pad under the motor and figure it was from a combination or the small leak and my bleeding. About a month ago I got/paid a Yanmar mechanic to help me trace down the air leak. He was great and we found the leak was due to a wrong size hose/fitting combo mismatch. He changed a fitting on the Racor and put proper size hose from Racor to lift pump. Motor ran great, started every time, didn’t have to bleed anymore. I did however notice I was still having diesel on the pads under the motor. Over the last month the amount on pad was increasing. Upon my investigation I saw that the leak was coming from around the top of the HP motor injection pump. Motor was still running great and starting with no bleeding needed. Even though we are not near him, we are actively cruising right now, I call the mechanic that fixed my air leak. We figured it was the o-rings that had become brittle and were leaking. He said it was not a hard job but suggested that it would be better to hire it out instead of DIY because to be very careful with springs and cleanliness when opening up the HP injection pump.I got a recommendation and hired someone. Let’s save the I can’t believe this guy story and just say I was not impressed with his cleanliness around the open HP Injection pump or handling of the springs. He got it back together with new orings installed. We also replaced all three fuel lines between the HP pump and injectors. We got the HP Injector pump primed. Bleed fuel all the way to the injectors. Got the motor started. It was running rough at low RPM. Running fine at higher RPM. No leaking fuel anymore. Since the orings have been done the motor is now hard to start. Before it would start at idle or 1/4 throttle right after pushing start button. Now it takes 15-30 seconds of cranking to get motor running. Once running it is way more rough and clunky at idle than it was. Above 1200 RPM it runs like it did before. I have run the motor for over an hour a couple of times without any issues while running. It will restart easily right after shutdown. But a few hours after shutdown it takes extended cranking to start again. Any help or ideas would be appreciated. I am thinking perhaps the mechanic got some debris in the open pump and screwed up the pump. Or maybe there was some debris in the new fuel lines that got pushed to the injectors. Could there still be air in HP fuel lines or the pump after hours of running. Is there a way to tell if it is the pump or the injectors?
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Old 26-01-2025, 13:24   #2
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Re: Hard Start after HP pump o-ring replacement

Since the engine runs fine at higher speeds, it's not the injectors. If it was, you'd never reach high speed.
Something isn't sealed right in the pump or line and small amounts of air is getting into the pump. Not enough to keep from starting but enough to cause excessive cranking until air is compressed and the pressure is built enough to open the injectors. It runs poor at idle because one or more injectors are still getting air. At high rpm you may still get some air but it's being masked by higher fuel flow. The air could be entering at the pump, but could be somewhere in the supply line that may have been jarred during rebuild.
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Old 26-01-2025, 19:42   #3
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Re: Hard Start after HP pump o-ring replacement

I assume that the orings you replaced were the ones that seal the delivery valve holders and my only suggestion would be that somehow the mechanic has reinstalled the delivery valve, the spring, the valve body or the copper washer incorrectly. You’re 100% correct about cleanliness when handling parts of the fuel injection pump and the proper method of removing the delivery valve assembly is to use tweezers and place the parts in a small tray filled with diesel fuel, no contact at all with skin or gloves. Its surprising how rough a yanmar runs at low rpm if the delivery is worn or the spring is damaged, I can post a screen shot of the valve if you don’t have a copy of the service manual, …..we remove one delivery valve every time the injection timing requires checking and adjusting.
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Old 28-01-2025, 17:23   #4
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Re: Hard Start after HP pump o-ring replacement

Thanks. We only changed the orings at the top. Only removed the cap with the spring in it and did not pull out the lower portion where the copper washer sits.

I did another bleed today into see of perhaps air might be issue. Did the bleed after tightening fuel line at pump. Could only tight#2-3 until I get an extension for my wrench. When bleeding at the injectors #2-3 had a nice obvious “squirt”. #1 bleeds but doesn’t have the “squirt”. Still hard to crank. Will try tightening #1 when I get wrench extension.

Wondering if perhaps #2-3 reseated on copper washer and #1did not. I check oil but no level increase or diesel smell.
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Old 29-01-2025, 13:06   #5
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Re: Hard Start after HP pump o-ring replacement

There’s a chance that the spring is crooked in the holder or on the valve, usually I use a short piece of wire ( as per the Yanmar manual) to keep the spring exactly where it needs to be then slide the holder down the wire and engage the threads. This is a bugger of a job on the GMF’s because the heat exchanger blocks access to the top of the pump.
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