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Fuel pressure problems continuing / possibly relocating the

 
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PostPosted: Fri Feb 17, 2017 5:30 am    Post subject: Fuel pressure problems continuing / possibly relocating the Reply with quote

When I had the fuel flow sensor in the tunnel it would fluctuate a lot with the fuel pump and I didn't like that. So I moved it so that it is between the fuel servo and the divider and it is accurate there.  I think it will work well for you in that position.

On Fri, Feb 17, 2017 at 5:38 AM, Dan Charrois <dan(at)syz.com (dan(at)syz.com)> wrote:
Quote:
--> RV10-List message posted by: Dan Charrois <dan(at)syz.com (dan(at)syz.com)>

Hi everyone.

I thought I'd report back that I've pulled apart most of the fuel lines, including those in the tunnel and unfortunately haven't yet found any blockage or cause for the low pressure I'd been experiencing (the tunnel fuel filter is completely clean, and there don't seem to be any leaks or issues with any of the fuel connections).  I'm still going to check further (and perhaps try bypassing a gascolator), but I seem to be quickly eliminating things my low fuel pressure problem is not likely caused by, rather than finding anything that it might be.  One suspect (however unlikely) still remains with the one way bypass valve around the boost pump, since the boost pump seems to bring the pressure up, and the bypass valve is only used with the engine pump.  But the valve seems to be cemented to the pump manifold with some sort of white compound, so I haven't been easily able to remove it to check.  Or perhaps the engine pump itself could be a problem, though it's factory new, so I'!
 m not sure how likely that is either.

But while I have everything apart, I'm thinking of possibly relocating my fuel flow transducer from the tunnel to somewhere after the engine pump (I'm not sure if the transducer is the culprit either, but putting it after the engine pump can't hurt, plus would give me more accurate readings with the boost pump on).  But where are people putting it? The most convenient location in the engine compartment would be to mount it to a bracket on the engine mount and locate it right after the engine pump, on the way to the throttle body.  But if it's right after the engine pump, would I really be accomplishing anything different than its current location right after the boost pump?  Would the engine pump cause similar problems in transducer accuracy if the transducer is placed there?

Thanks!

Dan
---
Dan Charrois
President, Syzygy Research & Technology
Phone: [url=tel:780-961-2213]780-961-2213[/url]


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Dave Saylor



Joined: 11 Jan 2015
Posts: 89
Location: GILROY, CA

PostPosted: Fri Feb 17, 2017 6:25 am    Post subject: Fuel pressure problems continuing / possibly relocating the Reply with quote

Dan,

I think the best place for the red cube is between the servo and the fuel distributor (spider).  I like the method shown in these pics.  It's an -8, but the idea is the same.  Fab a steel bracket that catches the two forward servo-to-sump mounting bolts.
I'd be looking pretty close at your engine pump at this point, or your pressure sender.
--Dave
[img]cid:ii_15a4c74fb413e6af[/img][img]cid:ii_15a4c74f9180647f[/img]
On Fri, Feb 17, 2017 at 3:38 AM, Dan Charrois <dan(at)syz.com (dan(at)syz.com)> wrote:
Quote:
--> RV10-List message posted by: Dan Charrois <dan(at)syz.com (dan(at)syz.com)>

Hi everyone.

I thought I'd report back that I've pulled apart most of the fuel lines, including those in the tunnel and unfortunately haven't yet found any blockage or cause for the low pressure I'd been experiencing (the tunnel fuel filter is completely clean, and there don't seem to be any leaks or issues with any of the fuel connections).  I'm still going to check further (and perhaps try bypassing a gascolator), but I seem to be quickly eliminating things my low fuel pressure problem is not likely caused by, rather than finding anything that it might be.  One suspect (however unlikely) still remains with the one way bypass valve around the boost pump, since the boost pump seems to bring the pressure up, and the bypass valve is only used with the engine pump.  But the valve seems to be cemented to the pump manifold with some sort of white compound, so I haven't been easily able to remove it to check.  Or perhaps the engine pump itself could be a problem, though it's factory new, so I'!
 m not sure how likely that is either.

But while I have everything apart, I'm thinking of possibly relocating my fuel flow transducer from the tunnel to somewhere after the engine pump (I'm not sure if the transducer is the culprit either, but putting it after the engine pump can't hurt, plus would give me more accurate readings with the boost pump on).  But where are people putting it? The most convenient location in the engine compartment would be to mount it to a bracket on the engine mount and locate it right after the engine pump, on the way to the throttle body.  But if it's right after the engine pump, would I really be accomplishing anything different than its current location right after the boost pump?  Would the engine pump cause similar problems in transducer accuracy if the transducer is placed there?

Thanks!

Dan
---
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President, Syzygy Research & Technology
Phone: [url=tel:780-961-2213]780-961-2213[/url]


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Tim Olson



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PostPosted: Fri Feb 17, 2017 6:46 am    Post subject: Fuel pressure problems continuing / possibly relocating the Reply with quote

Hi Dan,

I did not reply to your email a couple days ago but will
quick jump in now.

First, when you said your engine died on you, nobody
at that point will give you the guidance to not investigate
that. My engine has never once died when giving throttle,
and if yours did, everything should probably be checked out
unless you can find a legitimate cause. That said, this
all happened right after you tore some things apart,
which would leave areas of fuel lines with air in them.
I would expect unusual engine response until you get this
air out of the system. If you pull apart fuel lines,
you should disconnect the fuel lines after the fuel
pumps, and run the boost pump into a container for
a while and make sure to purge any air out of the lines,
before starting. That would minimize this a little.

Beyond that, nothing you stated in that email is
highly unusual. If you climb lower than 120kts or
so, and do an extended climb to 10,000', in my experience,
you have a high chance that after about 8,000'
at some point you may start to see a reduction in
fuel pressure. Some people say they never see it.
I know many who have. Unless you are looking for it
and have an audible alarm set you may never even know.
I set my yellow alert for 16psi, and red for 10 or 11,
and I never get a red alert, but I do stare at it
when it gets below 16. I usually let it go
and don't hit the boost right away, but first
lower the nose and climb at a higher speed, and make
sure I've leaned for climb. A reduction in fuel
requirement and temperature helps it. If not, the
boost goes on. I have no leaks in any fuel lines,
and nothing for blockages.

Now your other point was that you advanced the throttle
and the fuel pressure dropped. If you saw that video
that was going around on the forums a couple weeks ago,
this makes perfect sense. It also happens to me
many times. If I try a takeoff without boost pump,
within 1 second of going full throttle I may get a
warning, but by the time I can glance to the fuel
pressure gauge, the warning is gone. First, this is
good because it's a reminder that we should be using
the boost pump during takeoff. We should try to correct
our form if we aren't doing that. But second, just
like the video says, you can have high flow and low
pressure, or high pressure and low flow, but you're
going to get one or the other and that is determined
by the fuel servo. When you rapidly advance the
throttle, the fuel servo demands instantaneous
fuel flow. This flow causes lowered pressure in
the line after the engine pump, where the pressure
transducer is located. The pump stroke of course,
as the video shows, is variable because of the way
the arm and spring interact, so it may take a couple
of pump cycles for that diaphragm to move up and
down enough to start flowing more fuel to meet
this need. The pump has limits to how quickly it
can fill this reduction in pressure. In your situation
it was still worth checking for air leaks around the
pump inlet, but as these are factory built hoses and
steel fittings on the pump, you're not likely to find
a bad flare or something be the cause, so the
probability is low that you'll find something other than
a loose fuel hose. Anyway, without the boost pump on,
I would absolutely expect a very short term, momentary
loss of fuel pressure when quickly advancing the throttle.
The quicker the advance, the more likely you'll see it.
So none of that shocked me and caused me to think
you had an issue.

I doubt you do have any unusual issue, personally, but
as I said, with your engine stoppage, it's probably
the time to do as you did and tear it apart. But,
after not finding anything, prime those fuel lines
and put it together and see where you're at again.
The gascolators are something most of us don't have,
so perhaps you can look into those for flow
restriction. I wouldn't expect it there though.

Regarding your flow transducer, yes, when it's in the
tunnel it won't read accurately with the boost pump
on. It may fluctuate more too during operation. You
didn't mention which type you have. Mine is the FlowScan
in the RV-10 and the red cube in the RV-14. I don't
know how much restriction the FlowScan causes, but
if you have the same, maybe that is why we see
some of this where others don't. The thing is,
with the RV-10 fleet, you can't count on all of us
having everything 100% the same. Mine is 100% per
plans...except for the braided lines, which I DO
find have more restriction than solid lines, as well.
When building the RV-14 I compared the effort to blow
air thru solid lines vs braided and there is definitely
a difference. All these things can account for
small differences in what people report.
Moving your transducer may improve it's stability, but
I would find it unlikely to change your fuel
pressure reduction issues. It may, but I would be
skeptical until you try it and say it did. Personally,
I don't see enough variation (fluctuation) to worry
about it much, and my boost pump is off by 1000' on
takeoff so the effect on my totalizer value is minimal
and I don't worry about it. Beside that, by using
the boost pump and the reading being higher, it just
gives me that tiny bit of extra margin on remaining
fuel. Were it the other way, where it reduced my
margin by showing lower flow, I'd definitely change
it because I want more, not less, fuel than indicated
on the totalizer. But if you are motivated to move
the transducer, I say go for it. Do it, and let
us know how it goes. Just don't do it expecting it
to fix the pressure drop....let that be a benefit
if you get lucky.

I've only had mine flying for 11 years and 1230+ hours,
and only have experience with my RV-10 that is first
hand, so my info is only worth 1.5 cents with inflation.
In a few years, you will have your own first hand
experience to share when the next guy asks this question.
Tim


On 2/17/2017 5:38 AM, Dan Charrois wrote:
Quote:


Hi everyone.

I thought I'd report back that I've pulled apart most of the fuel
lines, including those in the tunnel and unfortunately haven't yet
found any blockage or cause for the low pressure I'd been
experiencing (the tunnel fuel filter is completely clean, and there
don't seem to be any leaks or issues with any of the fuel
connections). I'm still going to check further (and perhaps try
bypassing a gascolator), but I seem to be quickly eliminating things
my low fuel pressure problem is not likely caused by, rather than
finding anything that it might be. One suspect (however unlikely)
still remains with the one way bypass valve around the boost pump,
since the boost pump seems to bring the pressure up, and the bypass
valve is only used with the engine pump. But the valve seems to be
cemented to the pump manifold with some sort of white compound, so I
haven't been easily able to remove it to check. Or perhaps the
engine pump itself could be a problem, though it's factory new, so
I'! m not sure how likely that is either.

But while I have everything apart, I'm thinking of possibly
relocating my fuel flow transducer from the tunnel to somewhere after
the engine pump (I'm not sure if the transducer is the culprit
either, but putting it after the engine pump can't hurt, plus would
give me more accurate readings with the boost pump on). But where
are people putting it? The most convenient location in the engine
compartment would be to mount it to a bracket on the engine mount and
locate it right after the engine pump, on the way to the throttle
body. But if it's right after the engine pump, would I really be
accomplishing anything different than its current location right
after the boost pump? Would the engine pump cause similar problems
in transducer accuracy if the transducer is placed there?

Thanks!

Dan --- Dan Charrois President, Syzygy Research & Technology Phone:
780-961-2213



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PostPosted: Fri Feb 17, 2017 9:22 am    Post subject: Fuel pressure problems continuing / possibly relocating the Reply with quote

I relocated my Flowscan from the tunnel to between the pump and spider -
it resolved the inaccurate reading problem. (The problem was actually
pretty minor since I ran the boost pump for such limited amounts of
times but now it's just dead nuts accurate).

I simply cut the fuel line and inserted the flowscan unit wrapped in
head shield. I secured the ends of the fuel line but the flowscan unit
is floating so to speak. I just could see any reason to secure it
further. Many hours later - all okay.

Bill
Quote:
But while I have everything apart, I'm thinking of possibly relocating my fuel flow transducer from the tunnel to somewhere after the engine pump (I'm not sure if the transducer is the culprit either, but putting it after the engine pump can't hurt, plus would give me more accurate readings with the boost pump on). But where are people putting it? The most convenient location in the engine compartment would be to mount it to a bracket on the engine mount and locate it right after the engine pump, on the way to the throttle body. But if it's right after the engine pump, would I really be accomplishing anything different than its current location right after the boost pump? Would the engine pump cause similar problems in transducer accuracy if the transducer is placed there?

Thanks!


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Bob Turner



Joined: 03 Jan 2009
Posts: 759
Location: Castro Valley, CA

PostPosted: Fri Feb 17, 2017 10:37 am    Post subject: Re: Fuel pressure problems continuing / possibly relocating Reply with quote

I've been think of how to reply, but now Tim wrote it for me! I agree with everything he said. My FF is in the stock position, is (by my choice) 2% high (conservative) with boost pump off, and a little more with it on. I also get low fuel pressure warnings approaching 10,000' in a full rich climb. But now that I'm past break-in, it's just a reminder that I forgot to lean! The poor engine is flooded with fuel at full rich and 10K'.

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PostPosted: Fri Feb 17, 2017 11:28 pm    Post subject: Fuel pressure problems continuing / possibly relocating the Reply with quote

Thanks, everyone, for more great advice. I have some good ideas now (and thanks for the photo, Dave!) as to where to move my fuel sender (red cube) - I just wish I would have put it there in the first place!

It seems that low engine pump pressure on the takeoff roll and extended climb is relatively common - at least I'm not the only one experiencing it. Van's tech support wrote back to me as well to say they see similar issues with their factory RV-10 and encouraged me (as have many of you) to not worry about it too much if the engine pump can maintain pressure at cruise. What had me worried more than anything was when my engine quit during my runup.

For all my flights up until now I'd had a GoPro in the cockpit which has proven invaluable to help analyze things after the fact. As luck would have it, this time I forgot the GoPro at home, so I have to rely on my much less reliable memory. But with that said...

Quote:
On 2017-Feb-17, at 7:40 AM, Tim Olson <Tim(at)MyRV10.com> wrote:

That said, this
all happened right after you tore some things apart,
which would leave areas of fuel lines with air in them.
I would expect unusual engine response until you get this
air out of the system. If you pull apart fuel lines,
you should disconnect the fuel lines after the fuel
pumps, and run the boost pump into a container for
a while and make sure to purge any air out of the lines,
before starting. That would minimize this a little.

Tim, in and amongst all the other helpful things you said, I think you hit the nail on the head here, triggering a light bulb moment for me.

I'm pretty sure I didn't purge the air out of the lines when I refuelled the plane after having cleaned out the gascolators the first time - it never entered my mind. When I started the plane, the initial priming with the boost pump would have cleared out most of the air from the lines to the tank I had selected at first, which is why it ran and acted normally initially. But now that your comments had me second guessing the exact sequence of events, I'm pretty sure that I changed tanks right when I turned on the boost pump in preparation for taxiing for takeoff. When I turned off the boost pump a few seconds later to see if the engine pump was working (likely before the air pocket in the lines would have found its way to the engine), I saw fuel pressure start dropping dramatically. I thought it was the fault of the engine pump pressure problem I've been chasing, but in retrospect, I'm thinking now that since I likely had just changed tanks, it was right about when the engine was getting a big gulp of air from the unpurged portion of line to the other tank. For some reason, since I wasn't suspecting the tank switch would have mattered (since both gascolator screens were now confirmed clean), I unintentionally discounted it as unrelated.

At least that would perfectly explain why it died during my runup. And also serves as a classic example of my error in jumping to conclusions as to the cause, with prior conceptions of what I expected the problem to be. I was so fixated on judging the performance of the engine pump, I think I switched tanks without paying attention to how it would affect things.

So with that said, now that I have everything in my tunnel pulled apart anyway, I'm going to recheck connections, look for blockages, etc. to ensure everything is as it's supposed to be. But I now have a probable explanation as to why the engine quit during my runup, enough so that I'm comfortable taking the plane up for its next flight if I find nothing else wrong (and it does the next runup OK, of course). And naturally, I'm going to run the boost pump into a container, from *both tanks* for awhile before I reconnect the line to the throttle body to make sure they're properly purged for next time.

I've learned a few valuable lessons here:

- never assume that a problem is necessarily caused by what you expect it to be caused by.
- Running the boost pump while switching tanks was something I've always been told to do but never fully understood why it's important. Now I have a perfect example of why... and also know that leaving it running for a bit of time after switching tanks isn't such a bad idea either.
- Running the boost pump before going full throttle also makes a lot of sense - we can anticipate the upcoming higher need for fuel, so that it's there before it's needed, unlike the engine pump having to try and play catch up when it's caught by surprise.
- the people on the Matronics RV-10 list are an incredible resource Smile

I may still bypass one of the wing gascolators so I can do an apples to apples comparison as to if (or to what degree) gascolators affect things. If nothing else was found to be a problem, prior to this I was reluctant to close things up and go flying without knowing if the problem was potentially fixed. But now that I have an explanation that makes sense to me, I'm certainly anxious to give it another go.

Incidentally, Van's mentioned that they have a cooling shroud on the fuel pump of their RV-10 (as some of you do too) which seems to help with pressure problems in extended climbs. Since my climb where I saw fuel pressure dropping near 8000', I installed a blast tube to the fuel pump (like with the mags) as a quick and simple potential improvement (not as good as a shroud, but probably better than nothing). When I get the plane up next, I'll try another similar climb to see if it helps at all. If not, a shroud could be another improvement... though just running the boost pump in a higher altitude climb and leaning the mixture in the climb might be enough.

Thanks again for all your advice, everyone!

Dan
---
Dan Charrois
President, Syzygy Research & Technology
Phone: 780-961-2213


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PostPosted: Sat Feb 18, 2017 4:35 am    Post subject: Fuel pressure problems continuing / possibly relocating the Reply with quote

Dan reminded me that fuel issues can bite you when you least expect it.
When I was a baby pilot learning all the intricacies of my airplane I
had a mentor that shared his wealth of knowledge. One lesson was about
fuel exhaustion. There are some of us that, for various reasons, run a
tank dry. So, you fill up and put the plane away. The next flight you
start up and taxi for takeoff. The big question is how far will you go
before you exhaust the fuel in the lines? It's going to be different for
different planes. I had an AA-1B at that time that would start up, taxi
to the hold short line (it was close by) and make it through a quick
run-up ..... only to die approximately 3/4 or so down the runway in the
'simulated departure'. What an eye opener, and an important lesson that
has stayed with me for over 40 years. I've made that 'test' on every
plane I've owned over the years. Short of taking Tim's advice to break
the fuel lines at the servo and purge the lines, an extended ground run
on each available tank is cheap insurance.
Linn

On 2/18/2017 2:28 AM, dan(at)syz.com wrote:
Snip!!!
Quote:
I've learned a few valuable lessons here:

- never assume that a problem is necessarily caused by what you expect it to be caused by.
- Running the boost pump while switching tanks was something I've always been told to do but never fully understood why it's important. Now I have a perfect example of why... and also know that leaving it running for a bit of time after switching tanks isn't such a bad idea either.
- Running the boost pump before going full throttle also makes a lot of sense - we can anticipate the upcoming higher need for fuel, so that it's there before it's needed, unlike the engine pump having to try and play catch up when it's caught by surprise.
- the people on the Matronics RV-10 list are an incredible resource Smile
Snip!!!

Quote:
Thanks again for all your advice, everyone!

Dan
---
Dan Charrois
President, Syzygy Research & Technology
Phone: 780-961-2213

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PostPosted: Tue Feb 21, 2017 9:35 pm    Post subject: Re: Fuel pressure problems continuing / possibly relocating Reply with quote

To check for any flow restrictions, you should see at least 42 gph if you unhook servo inlet line and run boost pump.

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