Engine Failure / Bad Aux Fuel Pump

[hnorber]

This past Sunday my engine lost power a few seconds after rotation (1991 M20J).   Fortunately, I still had plenty of runway in front of me and had not yet retracted the gear, so the forced landing was really a non-event (no decisions to be made, and no special skills needed – just lower nose, short glide, bleed off some energy and plant the wheels).

My engine came back to life on the rollout.  After taxiing to parking, I noticed the aux fuel pump switch had ‘tripped’ to off at some point during the ordeal, and that the aux fuel pump was not working.  Looking at my engine data, it seems that fuel flow declined from 17.6 to zero in about 12 seconds (steady decline from 17.6 to 13.4 in 6 seconds, then 6.2, 2.2, 0.2 and 0 in the next readings at 2 second intervals).  The fuel flow went back up to 3psi after landing.  I’ve attached a screen shot of the JPI data.  I also notice that cylinder #1 EGT is below the other 3, and drops way way low when I pull power (I’ve seen that on a few other flights as well). 

My first question to the group is: even though the POH calls for using the aux fuel pump on takeoff, shouldn’t the mechanical pump be able to provide adequate (or at least some) fuel flow after rotation?  I seem to recall doing one or two go-arounds without remembering to add the fuel pump in the past, with no issues.

I haven’t had a chance to get back out to the airport and open up the cowl – but could my aux fuel pump have failed in a way that affects fuel flow generally?   Most obvious thought is that it ruptured or created a leak - but  I didn’t see any signs of a leak or smell gas after landing (although I have smelled gas after other landings in the past).

Hoping to get a bit more insight on what the problem might be!

Thanks in advance for any replies!!

-Howard

 

 

Engine Analysis (2).docx

[N6758N]

Sounds like your engine driven fuel pump is bad. The aux fuel pump can mask the failure of the main pump until it no longer works.

[peevee]

Our manual calls for boost pump off for takeoff. Does the j call for boost pump on?

[kortopates]

Our manual calls for boost pump off for takeoff. Does the j call for boost pump on?

Yes, it's a fundamental difference between Continental powerplants and Lycoming. Although Continental is starting to call for non-emergency use of the boost pumps in its latest installations like the M20 TN.


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[hnorber]

Right - the J POH calls for the aux pump during t/o.

To 6758N - interesting thought about the mechanical fuel pump, but it seems I would have noticed during cruise climbs or even inital climb since I generally turn off the aux pump at 1000 ft.  Also, the mechanical pump did seem to be providing enough fuel flow at idle, taxi and takeoff (assuming that the aux pump wasn't working the entire time).

Thanks for the responses so far!
 

[carusoam]

The electric pump is designed to supply enough pressure to pass through the mechanical pump to support the engine through the high FF of even T/O.

The IO550 automatically turns on the fuel pump at full throttle so it seems like the FP is not needed, but it is there.

Part of my departure T/O check list is to check to see FF is in place early on.  Airspeed alive, then FF...

In this type of failure both pumps are not working properly.  

It is really interesting that your FF data is recorded by the JPI.  It was so close to letting you know something was up but didn't finish the job.

hopefully you will be able to get more data out of it.

Expect OH on both pumps is in order.

PP ideas only, not a mechanic.

Best regards,

-a-

Edited May 11, 2017 by carusoam

[Yetti]

If it was a dukes and it exploded there is plastic pats that could go downstream. There is supposed to be a filter that keeps the parts from going to the mechanical

 

[Guest]

Either fuel pump should be capable of delivering enough fuel to run the engine at max power.  Both of yours seem to have issues.

As pointed out  Dukes pump can shed parts into the fuel system and take out the engine pump.  S/B M20-222 covers it, covers J models thru s/n 1016, below yours I think.

Clarence

[bradp]

This is another example of either fuel pump inop is an AOG situation.  

[ArtVandelay]

You talk about fuel flow but don't mention the fuel pressure?
Turn on the boost pump for cold start and note the pressure.
Check pressure after start.
Could be a failure with RSA fuel injection: broken diaphragm, etc.
Bits could have clogged the injector #1.

[M016576]

On 5/11/2017 at 0:00 PM, carusoam said:

 

The IO550 automatically turns on the fuel pump at full throttle so it seems like the FP is not needed, but it is there.

 

The IO-550A in my aircraft does not automatically turn on the aux fuel pump- I have to manually run it if I want it on.  And I do in the summer months (any time it's 25+ C outside)- it keeps the fuel from boiling in the lines on climbout (no cowl flaps on a missile)

 Perhaps that's a io-550G or Ovation only function?

[carusoam]

Dp...

Edited May 15, 2017 by carusoam

[carusoam]

Just now, carusoam said:

IO550g & n for the O...

Fuel pump options on the panel are Lo and Hi output.  Audibly you can hear an RPM change on the one Electric aux fuel pump...

The fuel system also includes the fuel selector with two return lines back to the Left and Right tanks as selected.

Unfortunately, there isn't a fuel pressure gauge to go with all of that.

The O doesn't have cowl flaps, just some enlarged openings around the dual exhaust pipes...

STC'd max FF is 27.2gph...

Go IO550! 

PP thoughts about the O fuel system only...

Best regards,

-a-

 

[tony]

The reason low wing aircraft have a boost pump is because the engine is higher than the fuel tank.  The boost pump is at the lowest point in the fuel system.  This insures there is a gravity feed to the pump and the boost pump lifts the gas to the engine.  In most cases there is enough of a siphon to maintain pressure to the engine that the boost pump doesn't do anything.  The POH has you turn on the boost pump at critical phases of flight (landing and take off) when the aircraft is experiencing maximum differential rate pressure changes to minimize the hazard, .  In addition to checking your fuel pumps, I would check you fuel tank venting system.  

[epsalant]

Just now, tony said:

The reason low wing aircraft have a boost pump is because the engine is higher than the fuel tank.  The boost pump is at the lowest point in the fuel system.  This insures there is a gravity feed to the pump and the boost pump lifts the gas to the engine.  In most cases there is enough of a siphon to maintain pressure to the engine that the boost pump doesn't do anything.  The POH has you turn on the boost pump at critical phases of flight (landing and take off) when the aircraft is experiencing maximum differential rate pressure changes to minimize the hazard, .  In addition to checking your fuel pumps, I would check you fuel tank venting system.  

What exactly is the best way to check fuel tank venting system ?  I've never seen (like in a Cessna 152/172) fuel dripping when the wing heats up in the sun...

[tony]

I'd run a piece of safety wire in the vent to make sure its not blocked with a mud dobber.

Edited May 14, 2017 by tony

[ArtVandelay]

I made some covers for the vents to prevent insect problems.

[mooney2201]

I had the same problem,,,,,send me your email and I can help you through this problem,,i will give you my phone number,,my email is mooney2201@aol.com...

[carusoam]

If a bug puts a nest in the tank vent on either tank.  The air flow into the tank can be completely blocked.  The flight may go one for a while without problems, depending on how much air is in the tank to begin with.  The pumps will be drawing enough of a vacuum that the wing skin on the top of the wing will start to oil can.

If you notice this happening, switch tanks...

It may be possible to relieve this vacuum challenge by opening the sump drain at your feet.  Expect air being drawn in this way is going to cause some fuel shortage to the engine.  I did not test this theory.  But I did see the oil can effect.

The other thing you may notice is the tanks being pressurized in the sun. During the pre-flight walk around, you get a hint of pressure relief when you open the tank's fuel cap.  This is a screaming hint something is wrong.  Mooneys don't have pressurized tanks.  No matter how new they are.

Similar experience: I got to buy a new fuel pump for my car this year.  The fuel filter blocked up over time and killed the fuel pump that was working extra hard.  Got a new filter too...

PP thoughts only.  But crummy memories are really hard to forget...

Best regards,

-a-

Edited May 15, 2017 by carusoam