Fuel "Control monitor" or "Signal conditioner"

[Ernie Martin]

Two points.

For Pete: Where does one find, or who would have, such a box? How does one find a shop that has one? Dealers only?

For Ed: From my experience, it's understandable to be frustrated, but not at the people. I went through it when my mechanic (who I rate highly) and we looked at every item and tried everything. It's just a very elusive system, especially without the right tools. We inspected every connector and lightly sanded them to remove any corrosion and opened pins and closed females for more solid contacts, including the ones behind the cluster mentioned by Pete (there's a thread in this Message Board about it). Remember that the system relies on very tiny signal levels of capacitance, so any minor impairments in the lines can affect readings. I think Pete is correct that it's virtually impossible to troubleshoot the system without the specialized box.

Ernie

[Pete Somers]

Sorry Ed I put Dave just me having a senior moment.

Ed
I am only trying to help and of course try to save you time and money, it goes to say that the newer the system these days the more test equipment is needed to fault find and calibrate the system, ie it would be nice to have a Garmin G1000 but who can repair it when it goes wrong, Garmin!

The fuel gauging systems in GA aircraft is rubbish, however the old float type could be made to work quite well, then Cessna went on to this superduper capacitance system and well you have the end result.

I have said that this system CANNOT be troubleshooted with a screwdriver and a DVM, you need a test box with the adapter cables.

Good luck and let me know.

Regards
Pete

[edasmus]

Ernie and Pete:

Thanks to both. Rest assured I am not frustrated at the people. Everyone is trying to help. I am very frustrated at the situation. After all man has had fuel gauges on every engine driven vehicle since the beginning of time. It seems to me that this should not be so hard. They are just fuel gauges. What was Cessna thinking?

[Pete Somers]

Ernie and Ed

Give somebody like Yingling a call and see if they would hire out a box, all of the Cessna twin engine airplane have this system so they must be around so that you can calibrate the system correctly. Surely you maintenance guys will have some contacts. Give Cessna a call and see if the box they made is still on the go.
I am very surprised that these airplanes are certified without fuel gauges and maintenance shops that have not got the proper equipment to fix a problem?

Regards
Pete

[edasmus]

Pete and Ernie,

I just returned from my shop with your email (Pete's) and amazingly my shop has your magic box. My mechanic says he has rarely had to use it as he was always able to solve these problems by repairing connections. He did say the test box is required equipment to have at a "Cessna Certified Repair Station" which my shop is. As I headed over to the shop, I was prepared to "pull the plug" on this enjoyable little project and live with intermittent fuel gauges but since they have the test box, I decided to let the saga continue. They should have the plane back in their shop by this afternoon (Chicago time) so stay tuned!

Ed

[edasmus]

Well, the problem is still not solved but I guess it is as good as it is gonna be. The good news is that the fuel gauges work about 98% of the time and are stable while they are working. We just cannot seem to completely eliminate the problem. My mechanic saw nothing unusual while utilizing the test box other than he could impact voltage readings simply by by puting his hands around wires. I have no explanation for that. This was not an attempt to wiggle wires to search for a loose connection (although we have done that plenty) but an attempt to simply see what happens if you put your hands around wires.

My original signal conditioner has been sent back to Aero-Mach for good because my shop was able to get that one to consistently fail with the associated behavior of the gauges. They were unable to get the overhauled conditioner to fail but I knew I did when I intitially installed it myself. During the install testing with the test box the overhauled box behaved perfectly but shortly into my first flight (before I left the ground) the problem reappeared. We may be chasing multiple problems here. Who knows......

So my plan is to just fly until the annual in August and see if I can make any correlations with the supposedly random brief failures. My shop is going to work more on the connections at the gauges but as I said, not until August. The airplane is back together now and is going to stay that way and is working well otherwise. If any major developments should occur, I will certainly pass it on. If anyone else out there solves this problem, please share!

[Pete Somers]

Ed
This sounds a good one! I wonder if you have a bonding problem with the tank units. The wires from the tank units to the conditioner are screened and that should not happen. If you squeezed the wire you will alter the capacitance. I think now you need to check the whole bonding of the tank units and the wing joints.
However that is as you say a job at the annual when the panels are off, have the pleasure of flying it for the summer, enjoy!

Pete

[edasmus]

Hmmmm....thanks Pete, I will share that thought with my mechanic!

Ed

[edasmus]

Just got an interesting phone call from Aero-Mach Labs. They told me after receiving my original signal conditioner back at their shop for the third time (after I decided to keep the "overhauled" unit), they bench tested it again and found 5 more failed transistors. This really makes me wonder if the "overhauled" unit I now have is any better than the original one. They did say that under warranty for one year they would be happy to give my overhauled unit that I now have a free "check-up" to see how it is doing. I think I will do that in August/September 2009 when the airplane goes in for annual.

[Pete Somers]

Ed
That is rather annoying, as these people have had the box twice or is it three times and found faults that during the first test should have been cleared. You know it is much like the UK now to get a unit repaired like yours is almost impossible, to get a radio repaired in the UK is the same. The skilled people are just not here any more.
The Skymaster is a easy airplane to both service and troubleshoot all you have to do is go back a few years and think logically.

Regards
Pete

[edasmus]

Such is life my friend....such is life!!!

[edasmus]

I just wanted to give an update on my fuel guages. I have been flying with the "overhauled" signal conditioner about 6 months now (about 50 hours) and everything seems to be in good working order. When we first installed the replacement signal conditioner, I would occasionally see both fuel guages drop off line for a few seconds and then come back to life. I have not observed that behavior of the guages in probably the last 25 hours or so. They seem to be steady, and accurate. We shall see how long it lasts but for now, all is well.

Ed

[tkirklindale]

i have a 1966 337a my engine gages SUX to say the least i want to throw them out the window at 10k any one out there have any idea where to get stc gages. or to fix these POS gages i have thanks tom

[hharney]

https://www.ultra-fei.com/index.php?page=alltwins

[dwbomber]

I got fed-up with bouncing needles and went all digital on the engine instruments. Electronics Int. makes the manifold pres. , Tach, Oil Temp, and Oil Pressure. I really like the digital and bar graph fuel level instrument. It was from an outfit in Canada, I will have to look in my paperwork for their name. It was a pain to calibrate cause ya have to climb up a ladder with 1 gallon at a time. (1 gallon = around 10 milivolts) I will attach a pic and hope I can get it right....DW Note: The fuel level is toggled to the left tank after a recent flight. OOOps, I forgot about the Volts & Amps...also from Electronic Int. When the tanks are full, the bar graphs look kinda cool as they are green at the top! With todays fuel prices, it reminds me of what I have in my tanks...A whole lotta Green. Before my next flight, I will top them off and post a pic if anyone wants to see...Cheers