Low fuel pressure... again

[Lance Murray]

It is very possible that the connection is an issue however it seems that ALL DA40's suffer from the fuel pressure issue. This includes G1000 and non G1000 VMS equipped airplanes. I haven't checked my 2002 airplane but I believe that they use different brand sensors and plugs.

I wonder if the capillary between the fuel servo and the pressure sensor is inadequately sized causing vapor in the system? Another thought is the location of the sensor directly connected to the servo. Many airplanes have the sensor on a T off of the fuel pump outlet and not on the servo. These are just guesses of mine at this point since nothing else seems to explain the issue. Unfortunately we are stuck with what Diamond gave us unless a mechanic is willing to file a 337 and change the fuel pressure pickup point. Diamond has ignored the issue within the fleet so we are on our own.

I may talk to my AMT about doing exactly this to see if it changes the indication issue. The part that would need to be added is a KB-090-T "Tee Fuel Pump Fitting" and a a modified AN823-4 with a 040" Capillary hole. I would have to plug the hole on the fuel injector also. Not a big deal but not sure a 337 covers this as a minor alteration or a major alteration. A major alteration requires an FAA sign off.

The parts look like this:

http://www.aircraftspruce.com/catalog/e ... -11908.php
http://www.aircraftspruce.com/catalog/e ... g00783.php

If anyone else has the time and the AMT that is willing to give this a try PM me and I will share my SWAG knowledge with you. It is also worth a call to Precision to ask their opinion of the location of the pressure sender.

I don't believe that Precision intended for a fuel pressure gage to be connected directly to the servo.

I'm sorry for not posting back about this. A couple of months ago, my fuel pressure reading became even more erratic, both high and low multiple times on every flight. I finally disconnected the plug and applied Stabilant to the connector, and my fuel pressure has been rock-solid ever since. My mechanic said he has changed the connector on several DA40's to fix this problem, so I ordered a new connector, but I thought I'd try the Stabilant first, since the connector is so easy to get to. If the problem comes back, I'll probably install the new connector next.

I wonder if those who had success by just swapping the sensors, actually "fixed" the problem by simply removing and reconnecting the plug, thereby reestablishing a good connection again...

[blsewardjr]

The rest of the story. In addition to swapping out the transducer, I tried cleaning the fuel servo. Debris was found, but the swapping and cleaning didn't change anything. After consulting with Glenn Lawler at Southtec Aviation, I had the engine fuel pump changed. The variation remains but at about 5 psi? higher, i.e., it now varies from 26-30 (the acceptable range is 14-35), with the outliers at 24 and 31. Apparently, this is not unusual so I'm going to continue to monitor but not make any further changes.

[haykinson]

I just had to fight this problem and wanted to share my experience.

On a long cross-country trip (Los Angeles -> Toronto) with family, my fuel pressure gauge started mis-indicating after a landing mid way through the trip. Specifically, it started varying between normal, zero, and max readings erratically and beeping at me. A short test on the ground showed that the gauge was not getting better regardless of RPM or mixture settings and didn't change with the fuel pump on or off. Everything else (fuel flow, engine performance, lack of fuel puddle on the ground) indicated a problem with the probe rather than an actual fuel problem. A local maintenance shop took the fuel pressure transducer off, cleaned the contacts, and put it back on and ran up the engine with no problems -- and on my next leg of the trip, everything behaved correctly from takeoff to landing.

One leg later, however, the gauge went bad again on takeoff. Fully believing this was an indication problem, I chose to continue. My trip very shortly after that took me to London, Ontario, where I had a maintenance shop look at the transducer. This time they took it off, cleaned it very thoroughly, performed a bunch of runups, and I even did a test flight -- everything was fine. We chose to not replace the transducer (it's an outrageously expensive part). As luck would have it, ten minutes after departing on my way back to California, the probe went bad again. I was on an international flight plan with border crossing times etc, so again I chose to continue and to fix it at my next stop (or the nearest Diamond facility to it). So, after tolerating yet another couple of hours of incessant beeping, this time with seeing the probe X-out at times in addition to max/min readings, I ended up at a shop in Ohio. There we swapped the oil and fuel pressure transducers (same part number), and this seemed to have fixed it. However, not wanting to end up with an errant oil pressure indication mid-flight, this time I just decided to pay the money to replace it.

Three days later (due to some part number confusion, and then problems with freight) the shop replaced the part, and I flew back to California with seemingly no problems in either fuel or oil pressure indications.

I'm not sure what the issue was -- the best I can tell is that the original transducer started failing unpredictably after exposure to engine heat. The probe sits close to exhaust piping, and not too far from the cylinder, so this is plausible, and would explain why a run up on a hot engine would show the problem while a post-maintenance run up would not. It would also explain why doing a pattern flight might not trigger the problem consistently. It doesn't fully explain the problem given the variety of situations where this was triggered, but it's the best I've got given all the troubleshooting we'd done.

[Pilot55]

On a flight from North Carolina to Florida at 9000 ft my fuel pressure would drop to 10 psi then up to 23 psi. Fuel flow would increase at the same time. Turned on electric pump to stabilize. This continued 6 or more times in a 2.5 hr flight. The next day at 3000 ft in slow cruise the engine stumbled and I immediately turned on the electric pump and all was fine. I left the pump on for a minute or two then turn it off. The engine did not stumble for the remainder of the flight. I am changing the mechanical engine driven pump for the return flight.

[Lance Murray]

Just a reminder. The Oil pressure sensor and the fuel pressure sensor are the same part number. They operate on different ranges. If you have a failure of one, try swapping it.

I have done this in the past and it worked for the duration of my ownership.

This is on the G1000 airplanes.

[DA40skyguy]

Recently on a flight from LAS to LGB, a club G1000 apparently had a double fuel pump failure (both the electric and the engine driven pumps) which resulted in an unscheduled landing at a dry lake bed near the NV/CA border. That's all of the information that I have at this time, other than the fact that intermittent fuel flow problems have been observed in the past.

[Rich]

Recently on a flight from LAS to LGB, a club G1000 apparently had a double fuel pump failure (both the electric and the engine driven pumps) which resulted in an unscheduled landing at a dry lake bed near the NV/CA border. That's all of the information that I have at this time, other than the fact that intermittent fuel flow problems have been observed in the past.

N165PS, perhaps?

This type of event might not show up in NTSB accident DB, due to what qualifies as an "accident". But we did wonder what the nature of the emergency was?

[Chris B]

That's all of the information that I have at this time, other than the fact that intermittent fuel flow problems have been observed in the past.

If you are able to get any additional color on this, please post. This is where the trend lines at Cirrusreports.com could be helpful, but the flight history may not be available.

I am particularly curious if the engine-driven pump gave any warning indications before total failure. I already know for sure that the electric boost pump can fail without warning.

Chris

[DA40skyguy]

If/when I learn more about the specifics of this event, I'll post it.
A question that I have concerns verification of the electric fuel pump's operation. According to the DA-40 AFM Normal Operating Procedures, the verification for fuel pump operation during a cold start is only "note pump noise" no mention is made of visual fuel pressure verification. However, during a warm start, fuel pressure noise AND fuel pressure increase is mentioned. Why is this?

4A.3.3 STARTING ENGINE
(a) Cold Engine
1. Strobe light (ACL)................................................................... ON
2. Electrical fuel pump ............................................................... ON, note pump noise
(=functional check of pump)

3. Throttle .................................................................................. 3cm (1.2 in ) forward from
IDLE (measured from rear of
slot)

4. Mixture control lever .............................................................. RICH for 3-5 sec, then
LEAN

5. Throttle ................................................................................... 1 cm. (0.4 in) forward from
IDLE (measured from rear of
slot)

(b) Warm Engine

1. Strobe light (ACL) ................................................................ ON
2. Electrical fuel pump ............................................................. ON, note pump noise
and fuel pressure increase

Rest of checklist essentially same as "cold start"

[Retz]

Quick question, you guys with the G1000 keep referring to checking the Fuel pressure gauge. I have an 06 with a G1000 and it doesn't display fuel pressure (just flow). Is there a way to enable display of fuel pressure on the G1000....perhaps in the mx page?

Thanks