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Another HPDI thread

Old 06-10-2021, 06:51 PM
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Hi all

200 HPDI with fuel issues. Last weekend running though chop and RPMs fell flat while on plane. Figured stirred up the 20 year old fuel tank and clogged VST, limped home. (Had the same issue last year. Brought to dealer for three months, sent out HPFP and injectors, replaced all filters etc. have put about 70-80 hrs and the symptoms return)

At home I replaced the water separator with a 2micron, VST filter and gasket, filter in the clear container under cowling. Took it to the river tonight, idled fine 5 minutes to the no wake bouy, took it up on plane running 3K+ RPM ran great for about 30 seconds then same symptoms, falls on its face down to 500RPM. Gave the bulb a few squeezes, idled around for a bit then tried again, got up and planed for another 30 seconds sounding great then falls flat again. Clear bowl had 3/4 fuel, bulb felt soft (but hard to gauge).

the intermittent nature of the issue leads me to believe it’s not a traditional filter issue as it runs great when it’s not starving for fuel. It’s like it’s running off the fuel in he VST and then practically stalls when the fuel runs out or can’t keep up. Could low pressure fuel pumps cause this?



Old 06-10-2021, 07:22 PM
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Will it run more than 30 seconds on plane if you continue to pump the primer bulb? If so, I would say either the low pressure fuel pumps are bad, or there is a restriction between the engine and the fuel tank. You can unbolt the low pressure pumps and pump the primer bulb until it’s hard. Look at the back of the fuel pumps for signs of leaking fuel. If so, replace them
Old 06-10-2021, 07:47 PM
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My 250's had a filter between the VST tank and HP pump. Looks like a large in line fuel filter. I replaced that every other year because I once had a similar problem.
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Old 06-10-2021, 08:19 PM
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I can try that stainless filter, though I’m pretty sure it was just changed last season, worth a shot. Have to figure out a way to put a decent clamp back on those fuel lines

am I wrong in thinking it’s not a filter? If the boat can run perfectly at high RPM for a short burst doesn’t that say it’s sucking the fuel from the VST tank fine? I feel like a clogged filter would be a more consistent linear bog and not so much 100 to 0.

maybe this is why I work with computers and not motors
Old 06-10-2021, 08:25 PM
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Originally Posted by Matta0413 View Post
My 250's had a filter between the VST tank and HP pump. Looks like a large in line fuel filter. I replaced that every other year because I once had a similar problem.
and after being on the fence to replace those your making me buy them now. the more i read up on these do the filters or do the time.
Old 06-10-2021, 08:26 PM
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Not sure if you are aware, but there are “mystery filters” on HPDI’s. If you search THT there are plenty of threads with info about these undocumented filters.
Old 06-11-2021, 03:24 AM
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Sounds like gas tank vent to me. take your cap loose and see. There are filters in the injectors which would be new with your injector service. There are filters in your HPIP that might need to be changed as well, but sure sounds like fuel tank not venting.
Old 06-11-2021, 04:17 AM
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Originally Posted by cws View Post
Not sure if you are aware, but there are “mystery filters” on HPDI’s. If you search THT there are plenty of threads with info about these undocumented filters.
thanks for the reply. I haven’t ruled these out yet - but I did send both the injectors and HPFP out last season and the basket filters would have been changed with this service.

I did order some to try, however. They come Monday. You never know
Old 06-11-2021, 04:57 AM
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I think your theory that everything is fine from the VST on is correct. So it is a restriction or leak somewhere from the tank to the VST. Is there a lot of smoke at startup? That would be another sign of the low pressure pumps which are a common failure. You could try running directly from a portable tank to bypass the external filter, primer bulb, and tank to start narrowing things down.
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Old 06-11-2021, 07:41 AM
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Disconnect fuel line from main tank...connect a temp. tank of fresh gas. Open the vent screw on your VST tank, drain the gas from the tank. If you do not want to disassemble your VST to check filter and inside of tank, leave screw out. Move to inline fuel cup filter assembly, drain fuel from fuel cup. Re-assemble. Disconnect upstream silver fuel strainer, blow through top check for obstructions. re-connect the silver strainer. After that, pump primer ball to flush fuel from temp tank through system. Keep draining fuel until the gas looks crystal clean. Put screw back in VST, pump bulb to fill. After you cycle your ignition 2-3 times, give it a shot. HPDI's are so fuel sensitive-I have been OCD with it on mine and still, started my season with the same. Just did this and back in the game. You have to go through process of elimination to rule out culprits. You will go nuts with all of the "could-be's and maybe's". Fuel, air, spark. I was never an outboard mechanic-I've learned through trial and error, reading copious amounts of forums on the topics, asking advice of others. They are great motors but any questionable fuel will ruin your fun.
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Old 06-11-2021, 04:26 PM
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Connect up a seperate tank and run it. See if it's in the motor or fuel system. I had an issue years ago with an older fuel line getting jammed up from using ethenol gas which the lines were not rated for. Boat was a 98" Contender 27' open. It would rev up to 4k but over that it would restrict flow to one engine. Isolated the culprit, replace the lines and was back in business. 200hpdi's need clean fuel sounds like you know that by running a 2 mic H2o/fuel filter which should catch most of the crap in the tanks. I use to keep my used VST filters when doing my maintenance as they were almost perfect. Good luck you'll get it figured.
Old 06-13-2021, 05:43 PM
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Update - solved! It was the low pressure fuel pumps. One of the diaphragms was completely shredded and the other was very stretched. It was running off the fuel in the VST then bogging when the LPFPs couldn’t recharge the tank.

thanks for all the comments and help.



Old 06-13-2021, 06:20 PM
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DO you know how long it has been since the LP fuel pumps were changed?

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