Fuel "Control monitor" or "Signal conditioner"

[edasmus]

Anyone out there know where I may find a fuel control monitor, Cessna part number C668004-0102 for a 1973 C337G model (no-turbo, no-pressure)? I have quotes from Cessna and Preferred Airparts for well over $1000 for new or used and a quote in the works from KRN Inc. I also found an old post from years ago on this site that actually listed the part I need from a parted out Skymaster. Hopefully, he will respond. I will go through the part locator flow chart I have seen on this site but I thought I would throw this out there in case anyone happen to have one in hand they don't want! Also, I am open for suggestions as to anyone who may be able to repair the one I have. My shop said this may be possible in the right hands. Apparently the plug that is on the circuit board has some lose pins and they need to be reworked or replaced. Thanks in advance! )

[JeffAxel]

you might give Aero-Mach Labs a call, they can repair that part.
www.aeromach.com
316-682-4678
they fixed mine and it works just fine...

[edasmus]

Awesome...thanks Jeff, I'll give them a try in the morning.

[edasmus]

Any recollection as to the cost of that repair? Thanks!

[JeffAxel]

they do time and materials, so my fix might not be the same as yours. It wasn't unreasonable though.....of course, what is reasonable for me might not be for you!! : )

[edasmus]

Thanks...I'll keep my fingures crossed! Believe it or not, after 20 years of airplane ownership I am rarely taken back by maintenance issues. This is just a crazy expensive hobby and that's all there is to it! Not for the faint of heart, that's for sure.

[edasmus]

Well, the part is getting shipped to Aero-Mach Labs today and it sounds promising. Thanks again and I'll keep everyone posted on the results. I will be out of town for a week or so but I will have updates as they become available.

[edasmus]

Well the signal conditioner was returned from Aero-Mach with apparently several items repaired that were "not per factory specs." The bill from Aero-Mach was $470 plus some shipping charges which seemed reasonable compared to any other options. My shop installed the unit last Friday ($140 to them) and calibrated the unit with the fuel gages. I got in the airplane yesterday (Saturday) and after visually inspecting the fuel tanks and seeing they were full, I turned on the master switch to see the fuel gages indicating EMPTY!!! ( %^&*(#@!$%^&%^$

After engine starts the gages came to life although occasionally still wiggling back and forth until reaching cruise at which they worked fine and indicated correctly as fuel was being used. I suppose something is loose somewhere so we will dig some more and I will share the info as it becomes available.

[Pete Somers]

That sounds good for the repair, but now down to finding out what is really wrong with the system.
Firstly replace the white connector on the signal conditioner.
Check the wing break plugs for any signs of corrosion.

The pins on both of these plugs and sockets suffer from a build up of corrosion and the only way to cure this is to replace them.

The plug and socket on the back of the instrument cluster again suffers from the above and needs to be cleaned.

The fuel indicating system on the 337G - H requires some looking after and any corrosion etc will deem the system useless.

Did your shop use a capacitance test box to calibrate the system??

Good luck
Pete

[Ernie Martin]

There's another thread on this with lots of info. I've checked everything and still get erratic readings. The signal level, especially at smaller fuel loads, is quite small, so any corrosion or other impedance screws up the reading. I've given up, take the readings when they're there (I never get a positive but inaccurate reading -- it's either correct or zero) and never take off without visual confirmation of fuel in the tanks.

Ernie

[Pete Somers]

Ernie
What you have to remember is that these aircraft are getting old now, you live down in Miami and The Bahamas and the sea air does take its toll on the electrics. The pins and sockets used on the white connector do suffer and do need inspecting, this affects not only the Cessna but all other makes as well. So even unplugging a connector cleaning and reconnecting may cure the problem. I have seen it over here with Aztecs/Navajo and a lot of Cessna 150/152/172 based at sea side airfields.

See you
Cheers
Pete

[Kim Geyer]

I usually find the problem is the connection in the wing root, the pins are usually corroded or loose. I'll replace them or clean them then try to close the female pins a little. I have also found the probe wiring inside the tank worn through from years of sloshing around and rubbing on the tank floor.
Hope this helps
Kim

[edasmus]

Thanks much for all the responses. I'll be back to the shop by Tuesday with a print out of all your input and we will get to work. I'll keep you posted. Thanks again!!! The help is greatly appreciated!

[edasmus]

Update on signal conditioner. At the end of last week my IA and myself checked every possible connection we could and all was well. My IA still felt the problem was in the signal conditioner. So I called Aero-Mach labs and told them of the problem still randomly occurring. They were very understanding and said they would be happy to take another look at my signal conditioner. So back it went for a second time to Wichita. I just spoke with the technician a few minutes ago and THANKFULLY, the first time he hooked the box to his machine, the box failed. YIPPEE! He has found loose capacitors and who knows what else (the technical talk is beyond me) but he feels these are certainly items that can cause the problems I have been having. He is continuing to work the problem until he is confident the signal conditioner is stable. He has found that the problem is affected by temperature as well as by vibration. Unfortunately the first time he had the box he did not do any temp or vibration checks. When we sent it back the second time, we specifically asked for these tests. As for the cost, my initial repair was $470. The worst case scenario is $702 if the box gets a complete overhaul. I'll keep you posted.

Ed Asmus

[Pete Somers]

Ed
Thats good news, however if you certify a part as serviceable the unit should have been checked in accordance with with the manufactures spec and clearly it was not.
It has cost you money to go through the wiring, plugs and to find out it is the box you first started out suspecting.

Not good.

Regards
Pete