PMDG FUEL IMBALANCE TROUBLE SHOOTING

[rsrandazzo 6,353]

Captains-We are still getting reports of wide inconsistencies in the fuel usage between tanks on the airplane, and some users still experiencing engine flamouts when the center tank fuel is exhausted.NEITHER OF THESE THINGS SHOULD BE HAPPENING!I've been trouble shooting this since early July and thought we had a good fix in place with SU1, but apparently that isn't the case.I've tried about 50 different variations to duplicate the flameout and have so far failed to duplicate....I HAVE been able to duplicate the excessive fuel usage from the right side tank but I haven't determined the cause yet.Here are some KNOWN CONDITIONS that each of you should be aware of:1) If the APU is running, our fuel control logic will prevent you from updating the fuel level in the left wing tank.2) We do not use the MSFS default fuel system logic because it does not work effectively for a Boeing airplane. (great for Cessnas tho...)3) Our system uses a series of "states" to define which tank/s to pull fuel from. If your Center tanks are running, you will get fuel from teh center tank, etc.4) There are a number of gates that force the direction of fuel flow given certain conditions. (i.e: when the center tank fuel is less than a certain level- the fuel system logic should force itself into the tank-to-engine configuration.)5) To kill any misconception about Xfeed... Only open the Xfeed valve if you want to draw fuel from the a single side of the airplane. If you aren't actively trying to balance fuel- leave the XFeed shut!6) MSFS will not allow a "tank-to-engine" configuration within the simulator. As such, when the airplane is in the T2E configuration, we have a nice little system that is quietly alternating the fuel valve between left and right tanks at a common timing interval. This simulates the T2E fuel consumption process marvelously. This also explains why you often see LEFT or RIGHT selected in the MSFS fuel valve selector in the FUEL menu. ;-)7) Our airplane SHOULDN'T care whether you change fuel from the external menu or from the internal menu. Some folks have found that they have success with using one menu as opposed to another. From our logic standpoint- it really shouldn't matter....so we'd be interested to hear more about user experience in this regard.8) All of this being the case SOMETHING is causing the fuel imbalance and the center tank flamout..... The question is: what?If you are experiencing the FLAMEOUT and/or the IMBALANCE:1) What version of FS are you using?2) Do you have "unlimited fuel" deselected? (I ask because after tens of hours of testing in FS9 I realized I had this box checked....duh)3) Have you manually set the fuel valve within MSFS before/during your NG flight?4) Which fuel menu did you use to set your fuel leve?5) What was the fuel level in each tank approximately at Takeoff...6) Had you conducted ANY crossfeed operations during the flight?7) Had you operated the APU at any time during the flight? Was it On/Off when the flamout occurred?8) Did you experience IMBALANCE, FLAMOUT or both?9) Please tell me you are running SU1-1, right? ;-)Thanks gents- looking forward to collecting some data from you to see if we can't beat this little bug back into it's hole...

[Guest Henri W]

Robert,I did have severe fuel imbalance problems when running the APU in flight. No flameouts, though. Last night I conducted a flight with APU off and everything worked perfectly. Cross feed worked, no fuel imbalance, fuel only from center tank when sufficient left in that center tank. I switched the fuel switches a lot, but everything worked like a charm. Again, this is only the case with APU off.My data:1) FS2002 on Win XP Pro2) No3) Did not matter4) FS2002 aircraft fuel menu5) 4000 - 1000 - 40006) Did not matter7) APU was on all the time8) IMBALANCE9) Yes, off course. But problem also occured with SU1Hope this helps.Best regards,Henri

[Guest Fortress]

Hi Robert,1) FS9 on WinXP Home2) Unlim Fuel IS deselected3) Centre pumps to OFF when fuel in this tank depleted. ('FUEL' annuciated)4) External5) Wing tanks 100% each, centre 5%6) No7) APU running on ground, off at circa 6000' on climb-out8) Both, but flameout (Eng2 only) only once9) Yes.I say the flameout happened only once but the imbalance occurs everytime. Apart from varying the fuel (question 5) the other steps are common to all my flights.Cheers,Paulhttp://www.strontiumdog.plus.com/sbird.jpgOfficially licenced by British Airways plc for use of name and logo[p]AMD XP2800+ Barton, Gigabyte GA-7NNXP nForce2, 1Gig Crucial PC3200 DDR 400MHz, Gainward 128 MB GF4-4200, SB Audigy, 3 x WD Caviar SE[/p]

[Hakkie 0]

1) What version of FS are you using? FS2004, WinXP Pro SP1 etc.2) Do you have "unlimited fuel" deselected? Yes3) Have you manually set the fuel valve within MSFS before/during your NG flight? No, I only use the valves in your panel, don't use any MSFS fuel related key assignments. I usually fly trips of around 1 hour, so center tank is empty. I fill in 0% in the FS2004 fuel menu of the 'Create a flight' section. Wing tanks are filled according to the fuel needed ofcourse. Then I start with cold&dark, provide power, start APU, switch on left/right fuel pumps, switch off/leave off center tank pump, start engines. All according standard procedures (I hope ;-)) Switch off APU. When I keep it like this, I always get a right tank fuel imbalance warning after some minutes of flight. I then select crossfeed and turn off the right pumps till the imbalance is gone. Then switch on right pumps, switch off crossfeed. From this point on the flow is good. No more imbalance warnings during the remainder of the flight.4) Which fuel menu did you use to set your fuel leve? FS2004 menu5) What was the fuel level in each tank approximately at Takeoff... Left/right at 99%, center tank empty6) Had you conducted ANY crossfeed operations during the flight? Yes, see point 37) Had you operated the APU at any time during the flight? Was it On/Off when the flamout occurred? No, APU off after engine start.8) Did you experience IMBALANCE, FLAMOUT or both? So far no flameout at all occurred, I guess because my short flights do not require center tank fuel? I've only seen the imbalance warning a lot.9) Please tell me you are running SU1-1, right? Sure! Used the remove tool, re-installed base and then SU1-1.Hope it's helpfull. Also, if I'm doing something wrong in my procedures, please let me know!EDIT:I did change Aircraft.cfg to show 'number_of_tank_selectors = 3'Henk-Jan

[Guest Fortress]

Sorry, I should've said 'no' I haven't manually set any fuel pumps from the MSFS menu - only the switches in the PMDG panel.Cheers,Paulhttp://www.strontiumdog.plus.com/sbird.jpgOfficially licenced by British Airways plc for use of name and logo[p]AMD XP2800+ Barton, Gigabyte GA-7NNXP nForce2, 1Gig Crucial PC3200 DDR 400MHz, Gainward 128 MB GF4-4200, SB Audigy, 3 x WD Caviar SE[/p]

[Guest boblj56]

1) What version of FS are you using?FS92) Do you have "unlimited fuel" deselected?yes3) Have you manually set the fuel valve within MSFS before/during your NG flight?No4) Which fuel menu did you use to set your fuel leve?I don't understand this question. I thought there was only one way to set the fuel level, and that is via File/Aircraft/Fuel an Payload. What is the other?5) What was the fuel level in each tank approximately at Takeoff100/20/1006) Had you conducted ANY crossfeed operations during the flight?No7) Had you operated the APU at any time during the flight? Was it On/Off when the flamout occurred?Used APU to start engines, shut it off after start.8) Did you experience IMBALANCE, FLAMOUT or both?Flamout when center tank was empty9) Please tell me you are running SU1-1, right? ;-)Yes of course. LOL

[Guest Dino_Giannasi]

...>8) All of this being the case SOMETHING is causing the fuel>imbalance and the center tank flamout..... The question is: what?Hi,mmmhhh, now I have a suspect: the running APU, at least for the fuel imbalance. Switching off the Apu immediately after engine startup resulted in a successful test, with no imbalance at the end of the flight, without the need to Xfeed. I was also able to refuel the left tank normally.I'm wandering whether the imbalance is related with the control logic preventing you to refuel the left tank with a running Apu. Anyway here are my answers.All the best, Dino Giannasi>1) What version of FS are you using?FS2004 and FS2002. Same problem. As told before now OK at least for FS2004 (to be confirmed in FS2002).>2) Do you have "unlimited fuel" deselected?YES (i.e. NO unlimited fuel)>3) Have you manually set the fuel valve within MSFS>before/during your NG flight?NO>4) Which fuel menu did you use to set your fuel level?Internal FS>5) What was the fuel level in each tank approximately at Takeoff...Left 51%, Right 51%, Center empty>6) Had you conducted ANY crossfeed operations during the >flight?Yes and no, but it doesn't matter.>7) Had you operated the APU at any time during the flight? Running = imbalance. Switched off = even drainage>Was it On/Off when the flamout occurred?Never experimented a flameout (never filled the center tank)>8) Did you experience IMBALANCE, FLAMOUT or both?Yes. No (see above)>9) Please tell me you are running SU1-1, right?Absolutely YES>Thanks gents- looking forward to collecting some data from>you to see if we can't beat this little bug back into it's hole...You bet... Joint work is the way to go.

[B777ER 2,485]

Uhmmm Henri, I guess you did not know this but PMDG has modeled the APU to suck fuel from the left tank while running. Why you are having fuel imbalance problems is because of operator error. If you keep the APU on during flight, you WILL have a fuel imbalance problem with the left tank draining faster than the right tank.

[Guest Henri W]

Well,Than it is even worse, because the RIGHT tank was being drained much faster than the left tank. Furthermore, the imbalance was much more than ever could be attributed to the APU, or does the APU use more fuel than the two engines together ;-)Best regards,Henri

[Guest Henri W]

Robert,With 2) = No I meant no unlimited fuel selected, i.e. did you have unlimited fuel DEselected = yes. Sorry for reading so poorly. It isn't even a Florida ballot. ;-)Best regards,Henri

[Guest tcable]

Here's an interesting one- I'm not seeing the imbalance with the 1-1 update, however I have seen a consistient flameout when the center tank runs dry, but it did not happen last night for the first time!Flameout only seems to happen to me if I've used teh APU for engine start.I have unlimited fuel unchecked.Tim

[carlan2uk 0]

1. 20022.na3.no4.FS 20025.7500,2000,75006.no7.only startup -off when flameout occurred8.Flameout9.SU1-1This is the first time that I have had flame out -I believe because Idid not notice the warning and did not turn off the centre tank pumps.If I do that when warned no flame out occurs and - I notice that the centre tank empties itself.David Pedder

[Guest]

Most peculiar thing... When I took a test ride to answer these questions just now, it seems everything worked fine! However, I started a flight with the engines running, 1% fuel in the center tank and 50% in the wingtanks. Shut down fuel pumps for the centertank as soon as the flight started (had 280 lbs in it), and started the APU, configured and set the overhead panel, and turned the APU back off (I've flown with the APU running all the time earlier). When I arrived, no fuel had been drawn from the centertank (still 280 lbs left), and the other tanks had an almost equal amount left (1900 and 1890 left to right).Just to test - after landing I turned on the center tank fuel pumps and gave full throttle to empty it. Guess what? The engine(s) did not flame out! I kept throttling, and as long as the center fuel pumps were on, the right tank fuel flow rate was much higher than the left. As soon as I turned the center pumps back off, fuel were drawn equally from both wing tanks.So I guess everything is normal with me all of a sudden then? Well, my plane anyway... *:-* At least when starting the flight with engines running (through the 'Create a Flight'-menu).Anyway, here are my answers:1. FS92. Deselected yes3. No, not through MSFS, only your panel4. The FS menu before starting the flight ('Create a Flight')5. 1% in the center tank and about 45% in each wing tank6. I did not touch the crossfeed valve this time (since everything went ok), and I think that is a first. I've always switched this several times during earlier flights when I had the flame outs and imbalance.7. The APU was off when I started the flight (with engines running), then I turned it on and 'pushed the right buttons' (I think) on the overhead panel, and turned the APU back off. It was running for about a minute.8. For the first time, no imbalance (well 10 pounds. Probably from when the APU was running) and no flameout, even when the center tank was empty. The APU was not running at the time the tank was empty.9. Running the latest service update yes.Final note: I've been running the APU through the whole flight earlier, and just recently learned that it was supposed to be off after engine start (well I sort of knew, but didn't bother to turn it off earlier). This was the first PMDG flight I turned it off during flight.When I started the APU before engine shut-down upon arrival, I noticed the fuel flow rate from the right tank was much higher than the left, so that has probably caused the imbalance for me (and others) earlier. I think maybe the APU is not supposed to drain that much fuel in real life...?Ok I'll stop now...Good luck sorting out the problem, and thank you for a great piece of software!Best regards,Bj

[Guest iandavid]

1. FS92. Yes3. No4. FS9 menu from full screen using ALT key5. 80%, 0%, 80%6. No7. On till 5000ft after takeoff8. Imbalance only L=35%, R=30%9. Clean re-nstall after removal with tool. Patched using SU1.1Flight time 1 hr.Paul Gardner

[Guest Sartori23]

1) What version of FS are you using?FS92) Do you have "unlimited fuel" deselected? (I ask because after tens of hours of testing in FS9 I realized I had this box checked....duh)Unlimited fuel is deselected3) Have you manually set the fuel valve within MSFS before/during your NG flight?No4) Which fuel menu did you use to set your fuel level?Fuel/Payload menu5) What was the fuel level in each tank approximately at Takeoff...L 99.9% C 12.0% R 99.9%6) Had you conducted ANY crossfeed operations during the flight?Yes7) Had you operated the APU at any time during the flight? Was it On/Off when the flamout occurred?APU for cold/dark start. Shutdown APU prior to taxi.8) Did you experience IMBALANCE, FLAMOUT or both?Flameout when center tank goes empty. I usually shut down the center tank pumps with about 120lbs remaining in the tank. Imbalance is slight with crossover open for entire flight, however I recall imbalace can get to be quite severe without it constantly open. I'll make a couple of flights later tonight and update with my findings.9) Please tell me you are running SU1-1, right? Of course :)Carl MooreSystem specs:WinXP Pro SP1P4 2.4ABIT BD7 RAID 512 Corsair DDR 2100ATI Radeon 9800 Pro Cat 3.6Hercules Game Theater XP Driver 6.09