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Suzuki Df-90 Making oil

Old 12-17-2019, 03:48 PM
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Default Suzuki Df-90 Making oil

2007 df90 making oil. Has about 350 hours. Just noticed its way over the fill line. Motor running fine. Seem to remember something about the VST can cause this, but VST is hard to get to on the df90 - going to try and research a little bit. anyone else had this issue?
Old 12-17-2019, 04:22 PM
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I’m pretty sure that year zuke has a mechanical cam driven fuel pump on the valve cover. The pump’s drive passes through the valve cover. I’ve heard of seals in the pump going bad allowing fuel to enter the engine crankcase via the fuel pump.
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Old 12-17-2019, 05:18 PM
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PM HighSpeedPursuit here on THT. He's got a good bit of experience with motors that age. Been a Suzuki owner forever.
Good luck.
Old 12-17-2019, 06:09 PM
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First check the low pressure pump. On vavle cover. Normal culprit. Is the seal. Then the float in the vst gets stuck. Check the injectors before touching the vst.
Old 12-18-2019, 04:14 AM
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Yes check the fuel pump for leaking gasket.

Its easy to check if its the VST, theres a vent hose from the VST to the crankcase. Pull it out of the crankcase, start the engine and wait a few minutes while it idles, if fuel drips out of the vent hose then the VST is blocked up or float level is wrong, usually just needs to be cleaned out and heights chexked.
Old 12-18-2019, 04:34 AM
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Oil looks really “clean” and smells of fuel, and is way over the full mark

will try to trouble shoot the lp pump and then vst
Old 12-18-2019, 04:56 AM
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Send sample out for oil analysis. Not Blackstone, though, because they don't accurately measure fuel dilution. Can't recall the name of the other company that does measure fuel dilution. Maybe someone will chime in.

2007 is out of warranty :-(, so you are on your own.....(save for the army of THT experts that will guide and misguide you......)
Old 12-18-2019, 07:08 AM
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Originally Posted by Freeportchris View Post
I’m pretty sure that year zuke has a mechanical cam driven fuel pump on the valve cover. The pump’s drive passes through the valve cover. I’ve heard of seals in the pump going bad allowing fuel to enter the engine crankcase via the fuel pump.

^^This, take the 2 10mm bolts out of the pump, pull the pump out of the but leave the hoses attached then have some one pump the fuel bulb and if it leaks gas out of the end, you need a new low pressure fuel pump.
Old 12-18-2019, 01:46 PM
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Originally Posted by pierdude View Post
^^This, take the 2 10mm bolts out of the pump, pull the pump out of the but leave the hoses attached then have some one pump the fuel bulb and if it leaks gas out of the end, you need a new low pressure fuel pump.

Not all failed seals leak that way. You also need to push in and let back out on the back side of the lp fuel pump (as if the cam was moving it)while priming the ball. The seal leaks alot In between the movement . I have seen them leak both ways.either way look for gas coming out the back side of the lp pump.
Old 12-20-2019, 12:16 PM
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pulled vent off VST and started motor . After about 30 seconds a steady dribble of fuel started coming out hose.

So looks like a little bit of a process to get to the VST on this motor. Can anyone verify the correct parts needed? Looks like the needle and seat seem to be the most common problem

Old 12-20-2019, 12:54 PM
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just needs cleaning.. I have never needed to replaced .only clean. It's a real easy task. If your in va I can help..


But word of wisdom. Unhook harness from intake. pull the whole intake with all hoses attached with the intake. Unbolt or detached everything that meets at the block or head that is attached to the intake. Do not unhook anything from intake side other then both fuel rails. Fuel rails come off attached to the intake.Leave injectors attach to fuel rail. And any gas lines attached. Unbolt lp fuel pump. Make sure you get all 4 black injector seal out before you lose them. After this is done whole intake come off in one giant piece. Now you have access to vst. Do not use a regular screw driver or impact gun. Use a impact driver like what you use on lower units. to get screw off the vst to split the shell. Otherwise you will stripe them btw they always strip. Buy extra vst Phillips bolts as. Some long smoke short. Rest is cleaning and reassembling. Btw I would drain fuel filter and bust open the fuel rails to clean the fuel system since your already in there. Now once you have it back together you need to prime the fuel system to get the vst back full
do not use the key first. Use primer ball to fill the system.
.


Takes me maybe 15-20 min at most to remove the intake and vst.
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Old 12-20-2019, 03:32 PM
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thanks for the help . SO maybe not as bad of a job as I was thinking ? THought I had read before it was several hours to remove intake. Will most likely try to do this in the next week or so. Any gaskets I need to order to put everything back together?
Old 12-20-2019, 04:28 PM
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Order the VST o-ring.
Old 12-21-2019, 07:50 AM
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ordered the VST o-Ring part # 15626-90J00 and new needle valve assembly 13370-99E00

will update after install
Old 12-21-2019, 08:21 AM
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I pulled my VST out through the top, leaving the intake intact. I have a 2008 115.

I ended up replacing my (vapor separator tank) due to multiple issues. See below.

You can remove the VST with out removing the intake manifold. You can take it out thru the top.

1. Remove black plastic flywheel (1 screw) cover and the black plastic intake cover (2x 10mm bolts from the side) right above the VST.
2. Remove the top oil pressure sender, to give you room.
3. Facing the front of the motor, remove the left side lower engine cover.
4. Drain the VST from the bottom screw that has the drain tube below it.
5. Remove lower fuel line from VST to lower fuel rail.
6. Remove lower 10mm bolt for the VST, not that you can get to it.
7. Remove the high pressure fuel filter & hose (2 x 10mm bolts).
8. Remove all other fuel hoses and small vent tub from the top of the VST.
9. Unplug electrical connector from the top of the VST to the fuel pump.
10. Remove the last 2 10mm bolts from the VST (the top bolt with a 10mm wrench and the lower with a 10mm ratchet wrench.
11. Remove VST from top.

My high pressure pump was not able to keep 38psi on the fuel rail, you will see in the pictures that the high pressure pump bushing that seals the neck of the pump to the VST was swollen from ethanol use and was cracked. This was causing the fuel to leak past the fuel pump back into the VST hence losing fuel pressure, causing drop in speed and sluggish running. This would allow the fuel pressure to bleed off making it harder to restart the motor after sitting for some time.

In the other pic you will see the neck of the fuel pump has a check valve and retainer, there was a small piece of plastic that broke off (brittle) that would keep the black rubber check valve and white plastic retainer in the pump. Now with that broke the check valve and retainer would shoot up into the high pressure fuel filter and would not be able to hold 38psi in the fuel rail when the motor is shuts off, causing the pressure to bleed off making it harder to restart the motor after sitting for some time.

In the bottom of the float side of the VST is the pressure regulator which didn't look great being on the bottom, I had no way of testing it and didn't want to take a chance of it not working and having to take out the VST for the second time. So by the time you replace the pump and the pressure regulator, you might as well by the entire VST unit with all new stuff including needle and seat.

On a side note after talking with the Suzuki mechanic he informed me if you have ethanol damage to the inside of the VST coating (surface damage due to water..corrosion) it allows tiny tiny particles of aluminum to bypass the fuel pump screen into the pump causing the pump to fail over time. This added to my decisions to by a complete new VST unit.

I hope this helps anyone with this issue.








Last edited by pierdude; 12-21-2019 at 08:41 AM.
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Old 12-21-2019, 04:56 PM
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Originally Posted by jeffro22 View Post
2007 df90 making oil. Has about 350 hours. Just noticed its way over the fill line. Motor running fine. Seem to remember something about the VST can cause this, but VST is hard to get to on the df90 - going to try and research a little bit. anyone else had this issue?
My 2002 DF115 did this. Turned out the culprit was the Regulator inside the VST.
Old 12-21-2019, 08:34 PM
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Yeah regulator failure, over pressurized it to overflow.
Old 12-22-2019, 01:03 PM
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Thanks for that write up pierdude. Will let you know how it goes
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Old 12-22-2019, 02:49 PM
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It's ok to cuss a little, letur rip.
Old 01-08-2020, 10:18 AM
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Got vst out and separated not sure what the issue is because to me it looks really clean and I don’t see any wear of dirt on needle or seat. Will check float height

the black rubber grommet seal on top of high pressure pump is swollen and slightly cracked so will plan to replace that while it’s apart

a little worried putting it all back together without seeing anything definitive on the issue.

Float actually seemed a little out of adjustment, so got that to the 43mm mark with digital calipers. original Measurement was almost 47mm (assuming I am measuring correctly)

Last edited by jeffro22; 01-08-2020 at 11:59 AM.

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