Forum: F-16 Procedures

Could be many things. If it gets to the point of going over the horn - it passes the iginition portion and that would lead me to believe it is a max fuelk valve problem. I would suggest you lay out the theory of ops and I do not like to shoot from the hip since I do not have a book in front of me. But after 22 years - I think it is a very possible chance.

By the way - everyone will be seeing the DESSC in the near future. You realise that relevant can be a long time in the AF. The DESSC inproved aircraft reliability immensely. The internal parameters allow for starts that the ESS controller does not allow.

Stu

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Joe, our dispatch truck does have a wireless laptop in it. He can easily access IMDS (CAMS) and internet for weather...good for lightning strike distances.

Could be many things. If it gets to the point of going over the horn - it passes the iginition portion and that would lead me to believe it is a max fuelk valve problem.

Na,n Thanks for the input ... I think we got it sorted

cchief16 called it with fuel bias … that is were the problem is. When it’s cold and you have a warm running JFS, go over the horn (CIT is in play now) you get the EGT spike in the older jets with an ESS controller (should be 2 second delay so system recovers) If controller is confused with the old software, it thinks overtemp (based on CIT) and off goes the JFS.

Seen something in the T.O. where talk about fuel bias should kick in @ 1000 rpm PTO instead of 4000 and that would sort problem. However Blk 15’s and below are going to be history in the USAF, so no need to spend “DA” money.

Newbie Joined: Jan 15, 2007 - 04:29 AM Posts: 8

Vark,

We have a jet at McEntire with the same problem. Mostly colder weather brings it on and only every so often (especially after sitting a couple days or so). I've wondered also about the Max Fuel valve and/or overtemp factor too. It's just one of those problems you could waste a whole lotta time on and maybe never fix all the way or just wait for a DESSC!

I would put money on it that it is your Fuel Bias Valve on your JFS Fuel Control. We have DESSCs on all our jets and have three jets with this particular problem. When the throttle is advanced to idle, the Fuel Bias Valve opens on the JFS Fuel Control. This allows more fuel to enter the JFS allowing it to reach 105% RPM to handle the load of starting the engine. Overspeed for the JFS is 108%. When you have a bad Fuel Bias Valve, it allows uncommanded fuel to reach the JFS causing either an overspeed or overtemp. Usually Fault 121. Following DESSC T/S, it tells you that there is uncommanded fuel and this condition is causing auto shut down. The fix by the book is to R2 your JFS Fuel Control. We changed out 6 on one of our jets and still had the same problems. Supposedly there was a bad batch coming from Depot. We finally received a 107 and disco'd and capped the cannon plug to the Fuel Bias Valve. Those three jets now start like champs. This fix is used by other countries and I believe the Navy. It somehow hasn't made it to mainstream AF yet.

For T/S purposes, you can disco the cannon plug and try to start it. If it works, submit a 107 and bag it.

Ok, I'm lost now. Disconnect the cannon plug on the fuel bias valve? The bias valve is in the fuel control and the fuel control only has one cannon plug connected to it. At Shaw we have Blk 50's and 9 out 10 times it was a bad EGT harness. We were allowed to fly with the DESSC installed but not after so many sorties since it is a temp fix. It just bends the normal operating limits since it still starts with any kind of fault. The 01 models we got came with the new DESSCs in them.

The weirdest problem I've had though was with one of our 97 models. After 54% engine RPM (GE), the JFS switch would unlacth, but the JFS would not shutoff until 15 secs later. Looking at the realtime read, the clutch disengaged but the bias valve and all fuel valves stayed energized. Our AFETS guy didn't believe me until I sowed him my self. In the end, it turned out to be faulty wiring. Strange huh?

Ok so this is gonna sound like shooting from the hip if you will here is something i have done in the past. No, it's not in the T.O. yet but I am working on it cuz we have had a lot of problems with this same issue. Unless your unit wants to spend money on a new JFS remove the fuel nozzle. Take a borescope and put it into the JFS where the fuel nozzle goes. Look closely and most likely you will see a mound of burnt fuel...otherwise known as "coking". If you see this, take a small flexible wire brush and brush the coking away. This should solve your problem.

What happens is that coking causes the fuel spray pattern to break up and shut the JFS down early due to fuel starvation and/or overtemp. Hope this helps you out a little.

Rick

Aren't the fuel nozzles changed out after so many starts per 6-11?? I know we had the fuel nozzles on bench staock at my last base. When it comes to bling JFS troubleshooting, start with the easiest and cheapest part 1st. Very Happy

Yes the fuel nozzle is supposed to be changed after 400 starts....however I know as well as the next guy this is not always accomplished....ie "pencil whipped" Even if the nozzle is changed as stated in the T.O. the coking problem still occurs.

Here's hoping my JFS gremlin will go away!

My bird's in Phase right now, and since it's going to the AEF this fall they're giving me free reign on fixing every little thing I can think of.

A couple months ago I changed ignitor, spray nozzle, dump (bugle) valves, ESS, and brake control valve. It was working fairly well but still had it's moments.

Now in Phase I have an ADG time change (sweet!) so I have a "new" refurbished ADG. While doing the R2 my CSD was showing signs of heat (paint peeling) so I have a new CSD. I had to remove my JFS accumulators for the keel removal (for ADG change) and one leaked out a decent amount of hydraulic fluid...so Hydro said order 2 new ones...I did. I went ahead and changed out all three fuel control shutoff valves too. I also changed my fuel filter on the FCV (book says inspect and clean). JFS itself looked good so I cleaned it up and changed the fuel filter screen on it too.

My base decided we're all going to have DESSCs now and the AEF birds have first dibs, so I'll be putting a new DESSC in before we do any engine runs. Hopefully everything will work as advertised. Very Happy

Weasel Keeper...just so you know you don't have to remove the accumulators when removing the keel beam....just one more headache and can of worms to open up. Hope you didn't take everything off the keel cuz that's one more big mess you don't need. Just disconnect the lines and drop it with everything still on it.

Oh yes, I left everything attached to the keel beam. I wanted to check out the accumulators anyway because of a slight bleed over that I couldn't find anywhere else. Sure enough one was tired. Hydro guy said they were going to start tracking all accumulators in the near future so he told me to order both.

I have had many experiences with JFS problems. We us the old ESS controllers. My JFS would not start, no fuel coming out of the drain during priming, start then auto shutdown, flame out, no start on first attempt, second attempt of the day JFS would start great. After replacing everything I could think off. (Months went by). I actually contacted DERCO; they are a distributer for Hamilton Sundstrand which makes the DESSC (not the RSL). They actually came to the base and did some tests for me. Same diagnostic information: DESSC tripped a flag and said fuel or ignition problem. Well duh! I think it says that for every problem. (Compliments of Weasel_Keeper). After further T/S ing and B/S ing. There were actually 3 problems. The fuel for the JFS works off of gravity (with out boost pumps running) from the opposite side of the aircraft. We used to leave our jets down on fuel at the end of the day (wanted to go drink beer; Air National Guard ). This is a big NO,NO. For many reasons. Anyways; come to find out there was a small crack in the fuel supply line for the fuel control; thus, leaving the jet down on fuel, the line would drain out causing air bubbles; causing starter problems. The last problem we believe (no evidence, no good test procedures), the JFS fuel shutoff valve was not opening all the way or not fast enough (possibly due to a week aircraft battery). After changing the aircraft battery, JFS fuel shutoff valve, and replacing the cracked line, I have never had a JFS problem to date. I am talking 3 years. If anyone needs any other information contact me @ matthew.combs@kellstrom.com

A year after Phase with perfect starts for most of that time until recently, my JFS problems started up again. I followed rickpump76's advice (as well as some other long time technicians at my base) and called engine shop to borescope my JFS. DESSC showed "late fuel ignition". Fail first try almost every time for the past few weeks and always started on 2nd. I finally "broke" it until the JFS problem was figured out (I'm tired of pumping). I changed the fuel nozzle (400 starts last week), ignitor, and ignitor lead. Borescope showed a lot of coking inside the fuel nozzle port and was partially blocking the ignitor boss. Looked like a damned coral reef! I thought about doing the safety wire cleaning trick, but upon further looks with the borescope I also found a crack in the combustion chamber near the turbine so I ordered a "new" JFS. I'm ready for ops checks tomorrow so we'll see how it works. Smile

Ya, a new JFS will normally solve everything. I got a brand new one out of supply a while back and was going to do a start 1 for leak and prime then start 2 for the ops ck.

It started in start 1 first time without a prime. Shocked

So I motored it to build my bottles back up, shut it off, had the guys look for leaks, then started her again in start 2.

Works fine and hopefully lasts a long time. Smile

Forum: F-16 Procedures

JFS auto shut down