t56jeff Posted April 1, 2010 Share Posted April 1, 2010 we are having a fuel enrichment problem.....note this is on an FCF aircraft so we can't pass until we get this fix.....it has us baffled.... enrichment works fine....until running engines for aprox 20-40 mins it is inop upon restart.and is consistant with the engine heating up......we have changed relay box, both LH and RH distro harnesses, enrichment valve, pressure switch, and last but not least speed switch.(pmesparky).....also we have "wrang out" all the wiring associated and used the "gray box" (electrial component test set) to aid in a portion of this...any help would be much appreciated...other than dynomite in the engine.... Quote Link to comment Share on other sites More sharing options...
Parrot Posted April 1, 2010 Share Posted April 1, 2010 Have you tried swapping the fuel flow indicator? Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted April 1, 2010 Share Posted April 1, 2010 So your engine starts WITH fuel enrichment when cold and it ALSO starts but without enrichment when hot... right? Quote Link to comment Share on other sites More sharing options...
Lkuest Posted April 2, 2010 Share Posted April 2, 2010 Looking at a schematic, the enrichment valve fuel gets ported back into the fuel control, so I suppose that is a possible cause, but first I would change the ignition relay and another 50psi switch for good measure in case the first new one was bad in the same way. I have seen ignition relays fail partially before, and from what you said, you haven't changed it yet. Quote Link to comment Share on other sites More sharing options...
herky400M Posted April 12, 2010 Share Posted April 12, 2010 It's during FCF, so are the engine anti icing systems on??? or have they been on during flight??? hot air passes over the CIT so it's influencing your start... greetz Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted April 13, 2010 Share Posted April 13, 2010 OK we need to hear from you... If you start with enrichment, STAY on the ground, shutdown the engine and restart with enrichment does it work? You have stated it is consistant with heated engines... so take out the flight varible and try it staying on the ground.... Another thought would/could/should be wing flex, engine torque flex anything that could "move" a wire just enough to open it and cause your enrichment to be inoperative..... Quote Link to comment Share on other sites More sharing options...
pjvr99 Posted April 13, 2010 Share Posted April 13, 2010 (edited) Another thought: if the starts are being done on the ground, is this engine being started using APU/GTC bleed air, or engine bleed air? And are the tank boost pumps being used, more specifically aux and/or external tanks? Edited April 13, 2010 by pjvr99 ... afterthought ..... Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted April 13, 2010 Share Posted April 13, 2010 "Another thought: if the starts are being done on the ground, is this engine being started using APU/GTC bleed air, or engine bleed air?" May need to clairify this as I can not make a connection between air source and enrichment other than a slower or faster rise to 16%. In flight there is no air source other than the propeller rotating in the airstream. "And are the tank boost pumps being used, more specifically aux and/or external tanks?" Again the source of fuel should not change the enrichment as the pressure used is downstream of the fuel pump assy. There is a connection with fuel source and the secondary fuel pump pressure light illuminating. Quote Link to comment Share on other sites More sharing options...
pjvr99 Posted April 13, 2010 Share Posted April 13, 2010 Natops, you hit the nail on the head. If the engine is being started with +-80psi instead of 30 to 35psi the spin up time is often markedly shorter. In turn, 50psi fuel pressure to cut off enrichment is also reached quicker. It is thus possible that the window of opportunity to see anything on the gauges is very small. A hot engine starts and spins up somewhat faster than a cold engine. Main tank boost pumps operate at 18 - 24psi, while aux and external at 30 - 40 psi. Basically this is already fuel pressure in the manifold, meaning that the time available to see some- thing before 50psi is reached, is reduced. I know, I'm looking for something highly improbable, but sometimes it's just those little things that trip us up. I honestly do hope it's a bad cockpit switch or broken wire ....... something regular and simple Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted April 13, 2010 Share Posted April 13, 2010 I understand what you are saying but at 16% the fuel pumps are turning at the same RPM no matter the time frame to get there. As for the fuel pressure, input pressure say 40PSI will be far less than the fuel pump output pressure and the fuel manifold pressure will be zero until 16%. The system is just waiting on 16% to allow fuel flow. The 50 PSI will be obtained at fairly the same time/rate.... I too hope it is simple and we get the outcome posted...SOON Quote Link to comment Share on other sites More sharing options...
victorp1 Posted April 14, 2010 Share Posted April 14, 2010 Why not disable the fuel enrichment as per Allison CSL-1567 dated Nov 30, 1996 with Revision 1. Quote Link to comment Share on other sites More sharing options...
tusker Posted April 14, 2010 Share Posted April 14, 2010 Good day. I was on the impression that fuel enrichment was disabled! Unless it is some old stuff bubbling up from the L-1011 RR engine ....RB211!!!!!!!! I will have to investigate on it!!. OK guys,..carry on!!!.................John Boy Quote Link to comment Share on other sites More sharing options...
pjvr99 Posted April 14, 2010 Share Posted April 14, 2010 Why not disable the fuel enrichment as per Allison CSL-1567 dated Nov 30, 1996 with Revision 1. Victorp1, do you have a copy of this CSL available? Quote Link to comment Share on other sites More sharing options...
aston56 Posted May 11, 2010 Share Posted May 11, 2010 Try unhooking the 50 PSI switch cannon plug. If you get enrichment with a hot engine, worse thing you'll have to do is stop start. At least you'll know if it's excessive fuel pressure at the enrichment kill switch or a bad signal from said switch. Had one once that the first start of the day would give you an enrichment start with good de-enrichment without enrichment selected. Every start after that was fine. Did all the steps you did with the enrichment valve/harness's, grey box etc.., finally R2'd the fuel control and never came back. Not exactly the same problem you're having though. Quote Link to comment Share on other sites More sharing options...
nosepicker Posted February 26, 2012 Share Posted February 26, 2012 PJVR99, here's the service letter you were asking for. Quote Link to comment Share on other sites More sharing options...
pjvr99 Posted February 26, 2012 Share Posted February 26, 2012 Thank you sir. As an aside to this discussion, one of our birds had a similar fault recently. Problem was in the relay box Quote Link to comment Share on other sites More sharing options...
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