OX 66 RPM drop

[ManateeBWN]

Thanks - will do.

[jb123]

i havent read each post thoroughly but have you checked/replaced the check valve after the lp pumps ?

[ManateeBWN]

Check valve after the low pressure pumps?
I have one prior the low pressure pumps

[jb123]

ooops yes, prior to lp pumps

[ManateeBWN]

O.K. - the valve prior to LP pumps has been checked!

I re-installed the VST today after cleaning everything (HP fuel pump filter, pressure regulator vlv filter) and also re-installed the main relay after workbench testing it.

Normal engine start and normal engine behaviour for 1.5 hrs with load between 4000 and idle. At the end I tried WOT - no complaints. Still: that´s exactly what the engine did last time before the problems reappeared.
For I did not have cutbacks I could not measure the HP fuel pump current under faulty conditions today.
Instead I tried to check the VST pressure regulating valve. I connected a vacuum pump to the top-connector and applied vacuum. I expected to see a pressure drop on the fuel pressure gauge, but I did not! Might that be the reason for my problems - or have I been too carefull on the vaccuum side? Has anybody a clue how the pressure valve on the VST works exactly, i.e. what is connected to what and senses what to regulate what?

I´ll take her out one of the upcoming days and try to go for 4 hours or so. If the behaviour is as expected problems will rise after that and when the engine is warm ...

[rodbolt17]

it connects to the intake manifold.
with the engine idling if you dissconect it you should see a 5-7 PSI increase in rail pressure.

[ManateeBWN]

Well - I did not observe that increase in rail pressure.
That might be a problem between the ears - I only checked p when I was trying to do something with the vac pump. If you ask me now what the fuel pressure was I saw??? I was looking for a change and did not see one while handling the vac pump. I know the fuel pressure was 33/32psi before. But I do not remember what value I read today.
Does the valve beeing connected to the intake manifold mean that the increasing vaccum when opening the throttle sucks the valve that in turn lets more fuel pressure reach the rail to satisfy the increased fule demand of the engine?

[99yam40]

If you think about it, the vacuum decreases when you open the throttle, and that causes increase in fuel pressure

[ManateeBWN]

Correct - my mistake!
But anyhow the pressure valve is meant to adjust fuel pressure to changing throttle positions. Highest pressure I can get at the manifold is surrounding air pressure. Therefore: as soon as my engine sputters again and I pull the tube to the valve I should hav max fuel pressure and no problems anymore?! Or the valve is faulty and nothing changes. At least an option to try.
I will check the increase again as suggested by rodbolt17 and make sure I look at the fuel p gauge when disconnecting the valve this time.

[ManateeBWN]

I did no new measurements up to now - however I ran the engine for about 5 hours now without any complaint. The only glitch I noticed was a little hickup when passing throught 2000 during acceleration.
I´ll be back when I have more news...

[smokeybear]

Manatee and Rodbolt...HELP!
I am glad I found this post. Sounds like manatee is experiencing the same problems that I have just encountered. My nephew took my boat out last Friday and instead of a fishing report I got a call that my boat wasn't running right. He stated it ran fine from the landing out to where we get bait and out to the inlet, about 30 minutes run time. After going through the inlet he rolled the coals to her and says she stalled and then picked back up. Did the same thing all day but ran fine while *****ing.
When he came in we replaced the fuel water seperator, cleaned the bowl on the side of the engine and drained the VST. There was a little water in the seperator but little to no trash in any of the components. We figured the only way to test was to fish on Sat. Nothing changed. Ran like a top for about 20-25 minutes. 3400 rpms seemed to be the magic number where she would stall...when I say stall I mean stall, she never sputters or acts like she's missing. Acts just like you've cut the switch off for one second and turned it back on.
I quess with all that said...where do I start?
Thanks in advance for the help guys!!

[99yam40]

best to start your own thread with all the info on your motor and problem.
Monitor fuel pressures

[smokeybear]

I appologize for infringing on someone elses "thread." Thought that sharing information was what this was all about. I'll start a new one.

[rodbolt17]

its not an "infringement" its that it gets confusing.
the OX66 motors were made in both 2.6 and 3.1L displacements some used CCS some did not.
were some minor variations in fuel and ign control.
however those minor variations can mean the difference in properly diagnosing a running issue.
some years back a dealership owner that I have known many years called me.
his tech had been troubleshooting a no spark condition on #5 cylinder.
2 days he says.
model number was an sx250txrz.
I told him to quit hunting that rabbit its designed to operate like that.
I also told him if you throttle up to 1000 RPM you will find no spark on cyl 2 as well.
an SX200TXRZ wont do that.
thats why we say start new threads including the model number.

[cichucki1]

Same problem. Found that the output from Voltage Regulator would go up to 17 volts when that happend. Replaced the rectifier/regulator two weeks ago, engine still runs like a charm.