Fuel pressure, sensor

[designrs]

The exhaust wrap company recommends a spray application to seal the material from oils etc. I'm not fond of the idea due to overspray issues.

Roger have you ever sealed the exhaust wrap with anything?
Thoughts?

[roger lee]

First post.
Don't worry about the sealing spray on the wrap. Most don't bother with it and it'll be just fine.

Fuel issues like they are discussing has had leaking supply hose. It sucks in air.

[designrs]

Roger, at what point would a leaking supply line typically be?
Are you talking before the gascolator?
Or anywhere before the fuel pump?

I assume that you would be referring to a loose clamp around the fitting?

[roger lee]

Check all clamps on the supply side. I wouldn't bother with the one at the wing or tank. If that wasn't tight you would have a fuel leak.

Have you ever tried a different pump?

[designrs]

Thanks will do.

I'm also thinking possibly the return line might be a factor.
What's the purpose of the fuel return line?
Is it really for safety or just excessive liability fears?

Some Rotax aircraft don't have the return line, and some are even running the newer fuel pumps.

Some feel the return is necessary for safety.
Others wouldn't feel safe flying with the return.

I've heard of some experimentals installing a restrictor jet on the return line.

Comments?

[drseti]

The return line is generally used on all Rotax installations that include both a mechanical and an electric fuel pump. When (during takeoff, for example) both fuel pumps are operating simultaneously, they can deliver fuel in excess of that required by the carburetors. In order to prevent overflowing of the carb float bowls, the return line routes the excess fuel back to a fuel tank.

[designrs]

Alright... good point.

Per my POH normal fuel pressure is 2.2 to 5.8 psi.
Recently I was rapid descending at 3,500 RPM's.
The Dynon indicated fuel pressure at 5.0 psi.

The plane was significantly pitched down.
If excess fuel flowed out of the carbs and into the catch pans with drainhose under the carbs, maybe the attitude would have caused fuel spillage.

So maybe the fuel return line is a good thing in that circumstance?
Yet I seem to recall some Rotax owners seeing fuel pressure as high as 7 psi?

[bstrachan]

The fuel return line also helps to prevent vapor lock. There IS a restrictor in this line, in order to maintain fuel pressure at the carbs. The theory is, circulating fuel back to the tank keeps the contents of the fuel lines in the engine compartment cooler, and any vapor bubbles that do form will go back to the tank through the return line. The fuel pump is designed to operate on liquid, not vapor.

[drseti]

When Rotax changed from the AC to the Corona mechanical fuel pump, the changed their maximim fuel pressure specification. Your AOI might not reflect this change.

[designrs]

Check all clamps on the supply side. I wouldn't bother with the one at the wing or tank. If that wasn't tight you would have a fuel leak.

Have you ever tried a different pump?

Will check the supply side clamps.
Also have the 15 psi Kavlico sender to install.

I did put a mechanical fuel pressure gauge on T-connected to check.
Was hoping for a low pressure warning from Dynon... unfortunately didn't happen.

Mechanical gauge consistently showed 1 psi over VDO / Dynon.
VDO gauge is 30 psi.
New Kavlico is 15 psi.
I'm hoping that the new sender will have better accuracy indicate higher pressures.

If that doesn't work I guess I must look at pump and rubber.

Fuel pump is new style installed less than a year ago.
It is my impression that when fuel pumps fail they fail totally?

[roger lee]

The correct VDO sender should be 0-30 psi. The correct VDO sender is 360-043. The senders are notorious for being off a couple of psi.
This may be the problem with a higher psi sender. The new sender may solve your problem. I would wait until you put the new sender in before you do anything else. That will at least rule a sender error in or out.

[3Dreaming]

I have also seen on oil pressure where the wrong sender was selected in the Dynon.

[designrs]

The new Kavlico senders require a firmwear update, 5.4.2 or higher. (done).
Instructions say fuel pressure sender is type 6.

[roger lee]

And make sure your D120 fuel pressure Max is reset to 7.2 psi.
The electric pump should not add more than .5-1.0 psi more than the mechanical. It was not always this way, but it is now. The recirculation line helps prevent vapor lock and keeps cool fuel circulating. You absolutely need one with the new pump. It will also help control pressure fluctuations. Over heated fuel hose can and will cause hiccups with vapor at times depending on the engine setup and installation.

[designrs]

The fuel pressure saga continues:

Recap:
Original VDO sender: occasional fuel pressure warnings, becoming more frequent.
New VDO sender: same as above

Mechanical check gauge: consistently showed 1 psi over VDO

New Kavlico sender (15 psi):
1) consistently shows about .5 psi over VDO
2) fuel pressure fluctuates at cruse 3.4 to 4.4, in 10 to 15 second intervals... apparently a more sensitive sender.
3) turning the electric pump on at cruise causes more rapid pressure fluctuation... but no low pressure warnings yet.
** 4) ON FINAL / Power to idle / boost pump on: low pressure warning, pressures very rapidly fluctuating between 1.7 psi and 4+ psi.

What next? (sigh)