another fuel pressure question

[carusoam]

I didn’t find the exact one...

But this one gives a hint of how the insert may fall out during disassembly...

https://shop.vansaircraft.com/cgi-bin/shop.cgi?ident=1592680810-32-678&browse=engines&product=va-128

It is essentially a long thin hole inserted into the elbow...

Somebody probably had to test a bunch of different holes to get the best one that works with the Mooney set-up...

 

If you have a bunch of extra energy... taking the elbow out to see what is inside, may be the next step... or consider the EI alternative...

EI makes the popular digital fuelP gauges people select before going all JPI primary...

PP thoughts only...

Best regards,

-a-

[carusoam]

75F,

See if the frequency matches the 2700 rpm... or a factor of 2, or 1/2...

45 beats per second?  (Would be impossible to see...)

It may depend on a gear driving the pump actuator... so the ratio may different than expected...

Searching for some logic...

-a-

[Guillaume]

On 1/8/2021 at 10:00 PM, 75_M20F said:

Hello Clarence,

Any idea what might be causing this (see video)? My fuel pressure gauge seems to keep time with the engine RPM. The higher the RPM the faster the needle oscillates back and forth. At times the needle is a blur even!  I have cleared out the fuel line from the gauge to the servo like you suggested in another thread by disconnecting both ends and blowing it out with compressed air. The problem is still there. Engine is the IO360 and it a pure mechanical gauge with a hose running from the gauge to the fuel servo.

Thanks! 

Michael

 

 

I had more or less the same issue years ago. 

See 

 

 

Replacing the mechanical fuel pump did the trick. 

The engine runs fine because the RSA 5 fuel servo works across a wide range of pressure by design. 

Edited January 10, 2021 by Guillaume

[carusoam]

Great video Guillaume!

The power of MS is awesome... 

 

Kind of a reminder... it may be the fuel pressure actually varying as the fuel pump is coming to the end of its useful life...

Might be a good time to check the age and hours on the mechanical pump...   have a look at the pump’s drain to see if anything is draining out...

Some times, when fuel leaks out on the ground... air leaks in in flight...

PP thoughts only, not a mechanic...

Best regards,

-a-

[75_M20F]

2 hours ago, Guillaume said:

I had more or less the same issue years ago. 

See 

 

 

Replacing the mechanical fuel pump did the trick. 

The engine runs fine because the RSA 5 fuel servo works across a wide range of pressure by design. 

Thanks for the information!

[75_M20F]

 

[Ragsf15e]

On 1/10/2021 at 6:40 AM, 75_M20F said:

 

Did you ever figure it out?

[75_M20F]

On 12/30/2021 at 12:46 AM, Ragsf15e said:

Did you ever figure it out?

Hello Mr. Rags,

Yes, I finally solved the problem (of the surging fuel pressure needle) after throwing a lot of money in all directions. Tried purging the fuel line to the fuel pressure gauge, that did not work (cheap fix if it works). Replaced the mechanical fuel pump, that did not solve the problem. Sent the MP/FP gauge out for overhaul, that did not fix the problem. I became suspicious it was still the gauge even after overhaul because now the MP needle was hanging up. So I sent it back to the overhaul place again, they worked on it and sent it back to me. Still had issues with the MP needle and I was tired of dealing with it. So I ordered this:

http://www.aerospacelogic.com/index.php?dispatch=products.view&product_id=106

Removed the old 1975 MP/FP gauge and installed this with a reducer plate so it would fit in the larger hold left in the panel.

Problem solved!!!! and as an added bonus fuel pressure line no longer enters into the cockpit.

Installed it all myself and had it signed off and paper work done by my mechanic.

 

 

[carusoam]

Great follow up 75F!

Thanks for sharing the details…

-a-

[65C_flier]

Hi all,

I am having a fuel pressure issue with my 78J (IO-360A3B6D) that sounds similar to some of the issues discussed in this thread. I am hoping somebody might have experienced the same symptoms as me and be able to offer some advice before we go pulling too much apart.

About 10 flights after my last annual I noticed that my fuel pressure on the ship's gauge during cruise climb with boost pump off was lower than its usual 25PSI (middle-of-the-green). It progressively got worse over the next few flights to the point where it dropped below the green (14 PSI) which really got my attention. Switching the electric boost pump on put the pressure back to around 23PSI. In cruise with boost pump off and leaned, the engine pump held around 23PSI.

After some troubleshooting on the ground it was much worse than I thought. I took a video (that I cant figure out how to upload). At full power run-up the fuel pressure drops from 23PSI to about 6PSI and the RPM drops about 100RPM (from 2650 to 2550). Fuel pressure then oscillates between 6-10PSI as the RPM oscillates between 2550-2650 every 5-6 seconds. The boost pump puts the pressure back to 23PSI and stable RPM 2650.

I had a look through my JPI data and I can clearly see the exact flight where this started. The graph below is an example from one of the later flights. The fuel flow starts to oscillate every 5-6 sec as soon as the boost pump is switched off. The EGTs follow. FF stabilizes for a few minutes when I reduce RPM for cruise climb, but then it returns. RPM is stable and I don't recall noticing the fuel px gauge oscillating at all during flight, but it is clear from the data that something is very wrong.

The engine driven pump was overhauled a few years ago and there is no sign of fuel or oil from the drain line. No fuel stains around the servo or anywhere else. No loose fitting that we could find. My assumption is that air is being sucked in through a gascolator o-rings (which were replaced last annual) or the fuel tank selector. Interested in any advice before we go and pull those apart. I am also worried that the old Airight fuel selector (610289-007) will be difficult to repair or impossible to replace.

 

Edited July 14, 2022 by 65C_flier
better pic

[N201MKTurbo]

Did you try switching tanks to see if the problem changed?

[Fly Boomer]

1 hour ago, 65C_flier said:

engine driven pump was overhauled a few years ago

Some really smart people around here will help you, but I would avoid exonerating any component because it was replaced, or repaired, or cleaned recently.

[PT20J]

Engine operation appears to verify that it is a real problem rather than an instrumentation issue.

The boost pump is plumbed after the fuel selector and gascolator so it's not clear why the pressure would stabilize with the boost pump on if the problem were air entering at either of those locations.

Fuel or oil leaking from the fuel pump drain line indicates a failure of one of the two diaphragms, but the pump should continue to function normally if the other diaphragm is intact.

The engine-driven pump is actually operated by an internal spring -- the engine drive compresses the spring, but the spring provides the pumping force. A weak or broken spring will cause reduced output.

I would suspect the engine-driven pump.

Skip

 

 

 

[65C_flier]

7 hours ago, N201MKTurbo said:

Did you try switching tanks to see if the problem changed?

Yes. Same symptoms.

[65C_flier]

3 hours ago, PT20J said:

Engine operation appears to verify that it is a real problem rather than an instrumentation issue.

The boost pump is plumbed after the fuel selector and gascolator so it's not clear why the pressure would stabilize with the boost pump on if the problem were air entering at either of those locations.

Fuel or oil leaking from the fuel pump drain line indicates a failure of one of the two diaphragms, but the pump should continue to function normally if the other diaphragm is intact.

The engine-driven pump is actually operated by an internal spring -- the engine drive compresses the spring, but the spring provides the pumping force. A weak or broken spring will cause reduced output.

I would suspect the engine-driven pump.

Skip

 

 

 

Thanks Skip. I had similar thoughts about the boost pump being downstream of the suspected leak so it shouldn't help,  but the tempest video linked a few times in this post seems to indicate the additional pressure might blow enough through to effectively get the engine pump going (at 11min 35sec). That might also explain why it works for a bit after RPM reduction,  but creeps back in.

I agree there is still a good chance it is the engine driven pump,  i just want to eliminate any easier options first.

[PT20J]

1 hour ago, 65C_flier said:

Thanks Skip. I had similar thoughts about the boost pump being downstream of the suspected leak so it shouldn't help,  but the tempest video linked a few times in this post seems to indicate the additional pressure might blow enough through to effectively get the engine pump going (at 11min 35sec). That might also explain why it works for a bit after RPM reduction,  but creeps back in.

I agree there is still a good chance it is the engine driven pump,  i just want to eliminate any easier options first.

I looked at the video again and it seems to indicate that the pump will quit working entirely if there is air in the system.

I have read various threads where air was speculated as being an issue, but I don't recall hearing from anyone who actually found that to be the problem. So, if someone has, please give us the details so we can all learn from it. Personally, I have never had a fitting that leaked air but not fuel, but my experience is pretty limited compared to those that work on this stuff daily.

Skip

[65C_flier]

Problem is fixed. It was either the fuel selector or the gascolator. On close inspection there was some slight blue fuel staining on the top of the gascolator bowl (shaw aero 1540-3), so a new o-ring kit was installed. The top of the fuel selector shaft looked pretty worn, but we ended up reinstalling for a ground run after the gascolator o-rings were installed and fuel pressure was good. Next flight, climbed to 8000ft and left the mixture rich. We saw about a 2 needle-width drop (to ~20 PSI), but assumed that was ok given the excessively rich mixture. Performed fine throughout the rest of the flight including go arounds.

Noticed a few drops of fuel coming from the sniffle valve drain line (sump breather line) after the flight which I had never noticed before, but I assume that is unrelated and not a problem (normal fuel injector draining?)

[Ragsf15e]

5 hours ago, 65C_flier said:

Problem is fixed. It was either the fuel selector or the gascolator. On close inspection there was some slight blue fuel staining on the top of the gascolator bowl (shaw aero 1540-3), so a new o-ring kit was installed. The top of the fuel selector shaft looked pretty worn, but we ended up reinstalling for a ground run after the gascolator o-rings were installed and fuel pressure was good. Next flight, climbed to 8000ft and left the mixture rich. We saw about a 2 needle-width drop (to ~20 PSI), but assumed that was ok given the excessively rich mixture. Performed fine throughout the rest of the flight including go arounds.

Noticed a few drops of fuel coming from the sniffle valve drain line (sump breather line) after the flight which I had never noticed before, but I assume that is unrelated and not a problem (normal fuel injector draining?)

Awesome! Sometimes these fuel pressure issues are pretty mysterious.  A little fuel drip out the sniffle valve after shutdown is indeed normal.

[carusoam]

Great follow-up C_F!

1) Blue stains outside, often lead to air going inside….

2) The engine driven fuel pump is strong enough to oil can the wings….

(has anyone seen an oil can collapse this century?)

3) to watch air exiting the fuel system… people put a clear hose on the fuel injector system while doing other tests like the baby bottle test for flow balance checking of the injectors

 

PP thoughts only…

Best regards,

-a-