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Suzuki DF115 Fuel Issues

Old 11-10-2020, 09:31 AM
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Default Suzuki DF115 Fuel Issues

good morning, I have a lingering issue with my boat motor that I can't diagnose. its a 2006 Suzuki DF115 with 250 hours. here is a list of everything I have replaced this summer (all OEM parts):

1) spark plugs
2) low pressure fuel pump
3) low pressure fuel filter
4) high pressure fuel filter
5) fuel/water separator filter
6) thermostat
7) primer bulb (not OEM)
8) oil/filter change
9) IAC valve (was throwing code)

here is the issue: the last 2 trips, we would drive 5000-6000 rpms for like 5 miles and you can see the rpms gradually start coming down until it gets to about 2900-3000 rpms, which it stays like that all the way back to the boat ramp. no codes were given. never has a problem idling. starts right up no issue. i have the suzuki SDS software that i hook up to and there are no codes. we recently dove into the VST thinking it would be trash in there causing our issues, VST was spotless and pump/screen looked new. verified i had no kinks in the fuel line anywhere and that there was no trash or anything in fuel tank. i'm also aware of the faulty plug in the exhaust system. we tried to replace it with the right one we found online but we ended up ripping hole in the side of the casing which we had to get welded so that issue has been resolved. I'm kinda dumbfounded now. hate to keep throwing parts at her but it sounds like a starvation of fuel but I just don't know from where. any help would be greatly appreciated. thanks
Old 11-10-2020, 09:38 AM
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Have you checked the anti-siphon valve on the tank? I had a mech tell me it was fine and couldnt fix my starvation issue and he replaced/checked a lot of the items you list. A week later i replaced it. All fixed.
Old 11-10-2020, 09:42 AM
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Originally Posted by zx7king View Post
Have you checked the anti-siphon valve on the tank? I had a mech tell me it was fine and couldnt fix my starvation issue and he replaced/checked a lot of the items you list. A week later i replaced it. All fixed.
thank you for the response, yes i looked and verified that there isnt a anti-siphon on the tank at all. verified that the vent was clear as well.
Old 11-10-2020, 09:51 AM
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Cool. That was driving me nuts and when the very experienced mechanic pulled it off the tank and inspected it and said it was fine i didnt know what else to do. One day i got a straight through fitting (no valve) to try it and sure enough no starvation issue. Then i put on a new AS valve. Its strange how mine looked/behaved correctly when inspected but no doubt was not functioning consistently. The other tell i had i switched lines on the motors and sure enough the other motor started having starvation issues. Good luck!
Old 11-10-2020, 10:02 AM
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Originally Posted by zx7king View Post
Cool. That was driving me nuts and when the very experienced mechanic pulled it off the tank and inspected it and said it was fine i didnt know what else to do. One day i got a straight through fitting (no valve) to try it and sure enough no starvation issue. Then i put on a new AS valve. Its strange how mine looked/behaved correctly when inspected but no doubt was not functioning consistently. The other tell i had i switched lines on the motors and sure enough the other motor started having starvation issues. Good luck!
it defiantly makes sense about the AS valve. i appreciate the help. hopefully we will have a resolution soon.
Old 11-10-2020, 10:50 AM
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I recently did all of the above.

my motor sat for 5 years prior to me acquiring it. Ethanol in gas had eaten my plugs and injectors and VST pump. replaced everything the gas touched. I still had trouble with it surging and finally was told to pull the injectors. BAM! Got some off Amazon and she runs like a banshee now. Best money I have ever spent! it was a $40 bet!!!! LOL


Old vs Amazon injectors


https://www.amazon.com/gp/aw/d/B01DVVWX0Y?psc=1&ref=ppx_pop_mob_b_asin_title https://www.amazon.com/gp/aw/d/B01DVVWX0Y?psc=1&ref=ppx_pop_mob_b_asin_title
Old 11-10-2020, 10:56 AM
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Have you checked the fuel pressure regulator? Or checked fuel rail pressure? The regulator is in the bottom of the VST....and maybe the needle and seat in the VST...I'll always replace the needle and seat if I pull the VST down anymore ....just a few thoughts...not too much else you haven't replaced, there's a rubber seal on the high-pressure pump that also has a tendency to swell up and not seal good...
Old 11-10-2020, 10:58 AM
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Originally Posted by Dblex View Post
I recently did all of the above.

my motor sat for 5 years prior to me acquiring it. Ethanol in gas had eaten my plugs and injectors and VST pump. replaced everything the gas touched. I still had trouble with it surging and finally was told to pull the injectors. BAM! Got some off Amazon and she runs like a banshee now. Best money I have ever spent! it was a $40 bet!!!! LOL


Old vs Amazon injectors


https://www.amazon.com/gp/aw/d/B01DVVWX0Y?psc=1&ref=ppx_pop_mob_b_asin_title https://www.amazon.com/gp/aw/d/B01DVVWX0Y?psc=1&ref=ppx_pop_mob_b_asin_title
thank you very much. $40 is not a bad way to start. i appreciate it. i will keep you posted.
Old 11-10-2020, 11:03 AM
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Originally Posted by Weekend-Hooker View Post
Have you checked the fuel pressure regulator? Or checked fuel rail pressure? The regulator is in the bottom of the VST....and maybe the needle and seat in the VST...I'll always replace the needle and seat if I pull the VST down anymore ....just a few thoughts...not too much else you haven't replaced, there's a rubber seal on the high-pressure pump that also has a tendency to swell up and not seal good...
i just verified the regulator. my suzuki manual states the pressure should release at 34.1 - 38.5 psi. mine released at 36 psi. i took the needle out and it had a little trash on it but i cleaned it off and is still a good pyrimid shape but replacing it would be easy while vst is out. the rubber seal on HP pump looks ok and seals pretty tight. probably wouldnt hurt to get a new one of those as well. thank you for the reponse.
Old 11-10-2020, 05:40 PM
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Weird problems like this can actually be electrically related. These engines demand good power supply otherwise they can do strange things.

As engines run power runs thru harnesses. Corroded wires and bad connections get hot. When they get hot, current is compromised, and things start to happen.

I would check and verify the condition of main battery cables, clean and tighten all battery connections, and check and clean all connections to main battery switch. And special attention to check the white wire and its fuse. That wire provides power to the engine ecu.

If you can get access to the harness, check and clean all connections that you can find.

Also you didnt say what the primer bulb does when the revs fall away - is it still firm or does it get soft or go flat?

Have you checked the tank breather to make sure its clear?
Old 11-12-2020, 08:03 AM
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Originally Posted by Moonlighter475 View Post
Weird problems like this can actually be electrically related. These engines demand good power supply otherwise they can do strange things.

As engines run power runs thru harnesses. Corroded wires and bad connections get hot. When they get hot, current is compromised, and things start to happen.

I would check and verify the condition of main battery cables, clean and tighten all battery connections, and check and clean all connections to main battery switch. And special attention to check the white wire and its fuse. That wire provides power to the engine ecu.

If you can get access to the harness, check and clean all connections that you can find.

Also you didnt say what the primer bulb does when the revs fall away - is it still firm or does it get soft or go flat?

Have you checked the tank breather to make sure its clear?
thank you for your response, i will definitely check the wire connections and the white wire. i have already cleaned the battery cables and tightened everything up. the primer bulb sucks in some when the issue occurs. i did check the vent to the tank and it was clear. As i was cleaning the VST and before i took the needle valve out to clean i blew down the tube just to see if the need valve was holding like it was supposed to and 2 small pieces of trash (looked like pieces of rubber hose) blew back in my face. we haven't test drove the boat after putting everything back together but with trash being stuck in the seat of the needle valve, i can see how that can restrict the flow of gas coming into the vst and which could limit my WOT. if that doesn't make sense please let me know. im learning as i go. thanks

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