yammie OX66 225 issue - The Hull Truth

the other tom · 12-04-2006, 01:18 PM

I believe this is a fuel delivery issue, but before tearing into it thought I would ask...
Motor starts and idles perfectly, warms itself up at high idle of 1200 then backs down to 750-800. In gear, idles up to 1400 rpms without issue, but moments after jumping on plane or running WOT, the engine will quickly lose rpms all the way down to zero, and then stop. Immediately it will start and idle perfrectly, but anything over 1500 - 1600 rpms and she shuts down again. Not a sputter or erratic rpm issue but quickly losing rpms down to nothing. All fuel system components are checked out up to and including the on-engine separator. This is the stbd engine of twins, and one single tank is delivering fuel to both. Racor is clean and never has had water, and when engine slows/stops, the bulb is firm and pumping it does not affect the stalling.

I am leaning towards the VST screen, since the bulb pumping would solve the fuel pump(s) if they were the issue....

Any other comments or ideas from experience? thanks

2005FishermanWinner · 12-04-2006, 01:23 PM

i am pretty sure there was a post a week or 2 ago that it was a weak fuel pump problem and the poster replaced them and said it was the problem , use the search button i guess

this is the post i was refering to , it was a different problem but might be worth taking a look , sorry

http://www.thehulltruth.com/forums/t...ode=1#M1260749

throwbacki · 12-04-2006, 02:45 PM

Had TWO VST filters replaced on my 200 OX66. Switched standard spin-on with 10 micron version after second replacement---changed every 50 hours. Problem went away. Apparently ethanol was cranking up old crud from my fuel tank.

willtalton · 12-04-2006, 06:35 PM

VST filter. Just changed one and the issue is resolved (knock on wood). Would not be a bad idea to have racor filter changed at same time.

John_Madison CT · 12-04-2006, 07:52 PM

I would bet a clogged VST filter. My last Ox66 was losing RPM's and I fixed it after replacing the VST filter.

If that's not it, check your low pressure fuel pumps or possible a dirty 02 sensor.

Dentman · 12-04-2006, 08:24 PM

Check out my posts, clogged VST filter than later in the season needle stuck in the seat.The needle was very etched and would not slide in and out of the smoothly. Ethanol is a PITA.

2870bw · 12-04-2006, 08:26 PM

low pressure fuel pumps

suncoug · 12-04-2006, 09:09 PM

I would strongly suspect the vst filter as well. I would also change out the low pressure pumps, if you haven't done so in a while. If these measures do not help, I would hook up the winky-blinky and see if there are any error codes. It is also possible that you have a defective TPS sensor.

I would also hook up the fuel pressure meter while running and see if the pressure drops below 35psi when the motor acts up, as it is possible that you may have a defective high pressure pump, regulator, or injectors.

Bucktail · 12-04-2006, 10:16 PM

Try the VST filter. From what I have learned, when the low pressure pumps start going up you will get a lot of smoking and the prime bulb will soften up. Being that you are not reporting any of these symptoms check out the VST. There are a number of articles on the NET on how to do it.

DreamWeaver21 · 12-05-2006, 02:14 AM

Just for kicks, why don't you pull the paper element out of the filter that is on the motor and give it a test run. One more thing to eliminate.

the other tom · 12-05-2006, 11:07 AM

wrenched for a few hours this morning, 3 possible problems. 1) the water separator filter on the engine had some debris in it, changed. 2) 3 of the low pressure fuel pumps had loose cover plate screws, possibly allowing air to be sucked or the vacuum to be lost 3) the VST screen had a covering of fine debris, which appeared to be particles of the grease I used to hold the gasket in when I changed the pumps 6 months ago. By smearing grease around the INSIDE edge of the gasket, it was able to be somewhat dissolved by fuel, and get sucked up into the screen. water test this afternoon, will report back. (installed new VST tank gasket without grease, and thoroughly cleaned the tank)

the other tom · 12-05-2006, 01:11 PM

update, Seatrial, up on plane, then WOT and after 3 minutes, same problem. Engine RPMs down to zero and shutdown. Immediately restart, and shutdown in 20 seconds. Pump bulb firm for ahwile, and runs for 3 minutes at WOT, then shutdown. Immediate restart = 20 second run again. Diganosis; low pressure pumps are not able to keep up with filling the VST tank at higher rpms, thus, the short fuse on the immediate restart and the longer run on a bulb-filled tank. Pull the low pressure pumps, slap a new set on, and bingo. problem solved.

John_Madison CT · 12-05-2006, 05:35 PM

Glad to read things are fixed. The beauty of the Ox66 engine is just how predictable they are when something goes wrong. Most of the time, RPM issues are either VST filtger, dirty 02 sensor or low pressure pumps. I learned a lot about the Ox66 from Rodbolt over at the Iboats.com forums. If you're not a member, sign up. Lots to learn from this guy !